commit 6fbd664c0cb76a1a54cc94b33caeec7dc38b3a06
Author: Torvald Riegel <triegel@redhat.com>
Date: Thu May 22 16:00:12 2014 +0200
New pthread rwlock that is more scalable.
This replaces the pthread rwlock with a new implementation that uses a
more scalable algorithm (primarily through not using a critical section
anymore to make state changes). The fast path for rdlock acquisition and
release is now basically a single atomic read-modify write or CAS and a few
branches. See nptl/pthread_rwlock_common.c for details.
* nptl/DESIGN-rwlock.txt: Remove.
* nptl/lowlevelrwlock.sym: Remove.
* nptl/Makefile: Add new tests.
* nptl/pthread_rwlock_common.c: New file. Contains the new rwlock.
* nptl/pthreadP.h (PTHREAD_RWLOCK_PREFER_READER_P): Remove.
(PTHREAD_RWLOCK_WRPHASE, PTHREAD_RWLOCK_WRLOCKED,
PTHREAD_RWLOCK_RWAITING, PTHREAD_RWLOCK_READER_SHIFT,
PTHREAD_RWLOCK_READER_OVERFLOW, PTHREAD_RWLOCK_WRHANDOVER,
PTHREAD_RWLOCK_FUTEX_USED): New.
* nptl/pthread_rwlock_init.c (__pthread_rwlock_init): Adapt to new
implementation.
* nptl/pthread_rwlock_rdlock.c (__pthread_rwlock_rdlock_slow): Remove.
(__pthread_rwlock_rdlock): Adapt.
* nptl/pthread_rwlock_timedrdlock.c
(pthread_rwlock_timedrdlock): Adapt.
* nptl/pthread_rwlock_timedwrlock.c
(pthread_rwlock_timedwrlock): Adapt.
* nptl/pthread_rwlock_trywrlock.c (pthread_rwlock_trywrlock): Adapt.
* nptl/pthread_rwlock_tryrdlock.c (pthread_rwlock_tryrdlock): Adapt.
* nptl/pthread_rwlock_unlock.c (pthread_rwlock_unlock): Adapt.
* nptl/pthread_rwlock_wrlock.c (__pthread_rwlock_wrlock_slow): Remove.
(__pthread_rwlock_wrlock): Adapt.
* nptl/tst-rwlock10.c: Adapt.
* nptl/tst-rwlock11.c: Adapt.
* nptl/tst-rwlock17.c: New file.
* nptl/tst-rwlock18.c: New file.
* nptl/tst-rwlock19.c: New file.
* nptl/tst-rwlock2b.c: New file.
* nptl/tst-rwlock8.c: Adapt.
* nptl/tst-rwlock9.c: Adapt.
* sysdeps/aarch64/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
* sysdeps/arm/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
* sysdeps/hppa/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
* sysdeps/ia64/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
* sysdeps/m68k/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
* sysdeps/microblaze/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
* sysdeps/mips/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
* sysdeps/nios2/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
* sysdeps/s390/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
* sysdeps/sh/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
* sysdeps/sparc/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
* sysdeps/tile/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
* sysdeps/unix/sysv/linux/alpha/bits/pthreadtypes.h
(pthread_rwlock_t): Adapt.
* sysdeps/unix/sysv/linux/powerpc/bits/pthreadtypes.h
(pthread_rwlock_t): Adapt.
* sysdeps/x86/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
deleted file mode 100644
@@ -1,113 +0,0 @@
-Reader Writer Locks pseudocode
-==============================
-
- pthread_rwlock_rdlock(pthread_rwlock_t *rwlock);
- pthread_rwlock_unlock(pthread_rwlock_t *rwlock);
- pthread_rwlock_wrlock(pthread_rwlock_t *rwlock);
-
-struct pthread_rwlock_t {
-
- unsigned int lock:
- - internal mutex
-
- unsigned int writers_preferred;
- - locking mode: 0 recursive, readers preferred
- 1 nonrecursive, writers preferred
-
- unsigned int readers;
- - number of read-only references various threads have
-
- pthread_t writer;
- - descriptor of the writer or 0
-
- unsigned int readers_wakeup;
- - 'all readers should wake up' futex.
-
- unsigned int writer_wakeup;
- - 'one writer should wake up' futex.
-
- unsigned int nr_readers_queued;
- - number of readers queued up.
-
- unsigned int nr_writers_queued;
- - number of writers queued up.
-}
-
-pthread_rwlock_rdlock(pthread_rwlock_t *rwlock)
-{
- lll_lock(rwlock->lock);
- for (;;) {
- if (!rwlock->writer && (!rwlock->nr_writers_queued ||
- !rwlock->writers_preferred))
- break;
-
- rwlock->nr_readers_queued++;
- val = rwlock->readers_wakeup;
- lll_unlock(rwlock->lock);
-
- futex_wait(&rwlock->readers_wakeup, val)
-
- lll_lock(rwlock->lock);
- rwlock->nr_readers_queued--;
- }
- rwlock->readers++;
- lll_unlock(rwlock->lock);
-}
-
-pthread_rwlock_tryrdlock(pthread_rwlock_t *rwlock)
-{
- int result = EBUSY;
- lll_lock(rwlock->lock);
- if (!rwlock->writer && (!rwlock->nr_writers_queued ||
- !rwlock->writers_preferred))
- rwlock->readers++;
- lll_unlock(rwlock->lock);
- return result;
-}
-
-pthread_rwlock_wrlock(pthread_rwlock_t *rwlock)
-{
- lll_lock(rwlock->lock);
- for (;;) {
- if (!rwlock->writer && !rwlock->readers)
- break;
-
- rwlock->nr_writers_queued++;
- val = rwlock->writer_wakeup;
- lll_unlock(rwlock->lock);
-
- futex_wait(&rwlock->writer_wakeup, val);
-
- lll_lock(rwlock->lock);
- rwlock->nr_writers_queued--;
- }
- rwlock->writer = pthread_self();
- lll_unlock(rwlock->lock);
-}
-
-pthread_rwlock_unlock(pthread_rwlock_t *rwlock)
-{
- lll_lock(rwlock->lock);
-
- if (rwlock->writer)
- rwlock->writer = 0;
- else
- rwlock->readers--;
-
- if (!rwlock->readers) {
- if (rwlock->nr_writers_queued) {
- ++rwlock->writer_wakeup;
- lll_unlock(rwlock->lock);
- futex_wake(&rwlock->writer_wakeup, 1);
- return;
- } else
- if (rwlock->nr_readers_queued) {
- ++rwlock->readers_wakeup;
- lll_unlock(rwlock->lock);
- futex_wake(&rwlock->readers_wakeup, MAX_INT);
- return;
- }
- }
-
- lll_unlock(rwlock->lock);
-}
@@ -233,10 +233,11 @@ tests = tst-typesizes \
tst-robust6 tst-robust7 tst-robust8 tst-robust9 \
tst-robustpi1 tst-robustpi2 tst-robustpi3 tst-robustpi4 tst-robustpi5 \
tst-robustpi6 tst-robustpi7 tst-robustpi8 tst-robustpi9 \
- tst-rwlock1 tst-rwlock2 tst-rwlock2a tst-rwlock3 tst-rwlock4 \
- tst-rwlock5 tst-rwlock6 tst-rwlock7 tst-rwlock8 tst-rwlock9 \
- tst-rwlock10 tst-rwlock11 tst-rwlock12 tst-rwlock13 tst-rwlock14 \
- tst-rwlock15 tst-rwlock16 \
+ tst-rwlock1 tst-rwlock2 tst-rwlock2a tst-rwlock2b tst-rwlock3 \
+ tst-rwlock4 tst-rwlock5 tst-rwlock6 tst-rwlock7 tst-rwlock8 \
+ tst-rwlock9 tst-rwlock10 tst-rwlock11 tst-rwlock12 tst-rwlock13 \
+ tst-rwlock14 tst-rwlock15 tst-rwlock16 tst-rwlock17 tst-rwlock18 \
+ tst-rwlock19 \
tst-once1 tst-once2 tst-once3 tst-once4 tst-once5 \
tst-key1 tst-key2 tst-key3 tst-key4 \
tst-sem1 tst-sem2 tst-sem3 tst-sem4 tst-sem5 tst-sem6 tst-sem7 \
@@ -303,7 +304,7 @@ test-xfail-tst-once5 = yes
tests-nolibpthread = tst-unload
gen-as-const-headers = pthread-errnos.sym \
- lowlevelcond.sym lowlevelrwlock.sym \
+ lowlevelcond.sym \
unwindbuf.sym \
lowlevelrobustlock.sym pthread-pi-defines.sym
deleted file mode 100644
@@ -1,16 +0,0 @@
-#include <stddef.h>
-#include <stdio.h>
-#include <bits/pthreadtypes.h>
-#include <bits/wordsize.h>
-
---
-
-MUTEX offsetof (pthread_rwlock_t, __data.__lock)
-NR_READERS offsetof (pthread_rwlock_t, __data.__nr_readers)
-READERS_WAKEUP offsetof (pthread_rwlock_t, __data.__readers_wakeup)
-WRITERS_WAKEUP offsetof (pthread_rwlock_t, __data.__writer_wakeup)
-READERS_QUEUED offsetof (pthread_rwlock_t, __data.__nr_readers_queued)
-WRITERS_QUEUED offsetof (pthread_rwlock_t, __data.__nr_writers_queued)
-FLAGS offsetof (pthread_rwlock_t, __data.__flags)
-WRITER offsetof (pthread_rwlock_t, __data.__writer)
-PSHARED offsetof (pthread_rwlock_t, __data.__shared)
@@ -150,9 +150,16 @@ enum
| PTHREAD_MUTEXATTR_PROTOCOL_MASK | PTHREAD_MUTEXATTR_PRIO_CEILING_MASK)
-/* Check whether rwlock prefers readers. */
-#define PTHREAD_RWLOCK_PREFER_READER_P(rwlock) \
- ((rwlock)->__data.__flags == 0)
+/* For the following, see pthread_rwlock_common.c. */
+#define PTHREAD_RWLOCK_WRPHASE 1
+#define PTHREAD_RWLOCK_WRLOCKED 2
+#define PTHREAD_RWLOCK_RWAITING 4
+#define PTHREAD_RWLOCK_READER_SHIFT 3
+#define PTHREAD_RWLOCK_READER_OVERFLOW ((unsigned int) 1 \
+ << (sizeof (unsigned int) * 8 - 1))
+#define PTHREAD_RWLOCK_WRHANDOVER ((unsigned int) 1 \
+ << (sizeof (unsigned int) * 8 - 1))
+#define PTHREAD_RWLOCK_FUTEX_USED 2
/* Bits used in robust mutex implementation. */
new file mode 100644
@@ -0,0 +1,911 @@
+/* Copyright (C) 2015 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <http://www.gnu.org/licenses/>. */
+
+#include <errno.h>
+#include <sysdep.h>
+#include <pthread.h>
+#include <pthreadP.h>
+#include <sys/time.h>
+#include <stap-probe.h>
+#include <atomic.h>
+#include <futex-internal.h>
+
+
+/* A reader--writer lock that fulfills the POSIX requirements (but operations
+ on this lock are not necessarily full barriers, as one may interpret the
+ POSIX requirement about "synchronizing memory"). All critical sections are
+ in a total order, writers synchronize with prior writers and readers, and
+ readers synchronize with prior writers.
+
+ A thread is allowed to acquire a read lock recursively (i.e., have rdlock
+ critical sections that overlap in sequenced-before) unless the kind of the
+ rwlock is set to PTHREAD_RWLOCK_PREFER_WRITERS_NONRECURSIVE_NP.
+
+ This lock is built so that workloads of mostly readers can be executed with
+ low runtime overheads. This matches that the default kind of the lock is
+ PTHREAD_RWLOCK_PREFER_READER_NP. Acquiring a read lock requires a single
+ atomic addition if the lock is or was previously acquired by other
+ readers; releasing the lock is a single CAS if there are no concurrent
+ writers.
+ Workloads consisting of mostly writers are of secondary importance.
+ An uncontended write lock acquisition is as fast as for a normal
+ exclusive mutex but writer contention is somewhat more costly due to
+ keeping track of the exact number of writers. If the rwlock kind requests
+ writers to be preferred (i.e., PTHREAD_RWLOCK_PREFER_WRITERS_NP or the
+ no-recursive-readers variant of it), then writer--to--writer lock ownership
+ hand-over is fairly fast and bypasses lock acquisition attempts by readers.
+ The costs of lock ownership transfer between readers and writers vary. If
+ the program asserts that there are no recursive readers and writers are
+ preferred, then write lock acquisition attempts will block subsequent read
+ lock acquisition attempts, so that new incoming readers do not prolong a
+ phase in which readers have acquired the lock.
+
+
+ The main components of the rwlock are a writer-only lock that allows only
+ one of the concurrent writers to be the primary writer, and a
+ single-writer-multiple-readers lock that decides between read phases, in
+ which readers have acquired the rwlock, and write phases in which a primary
+ writer or a sequence of different primary writers have acquired the rwlock.
+
+ The single-writer-multiple-readers lock is the central piece of state
+ describing the rwlock and is encoded in the __readers field (see below for
+ a detailed explanation):
+
+ State WP WL R RW Notes
+ ---------------------------
+ #1 0 0 0 0 Lock is idle (and in a read phase).
+ #2 0 0 >0 0 Readers have acquired the lock.
+ #3 0 1 0 0 Lock is not acquired; a writer is waiting for a write
+ phase to start or will try to start one.
+ #4 0 1 >0 0 Readers have acquired the lock; a writer is waiting
+ and explicit hand-over to the writer is required.
+ #4a 0 1 >0 1 Same as #4 except that there are further readers
+ waiting because the writer is to be preferred.
+ #5 1 0 0 0 Lock is idle (and in a write phase).
+ #6 1 0 >0 0 Write phase; readers are waiting for a read phase to
+ start or will try to start one.
+ #7 1 1 0 0 Lock is acquired by a writer.
+ #8 1 1 >0 0 Lock acquired by a writer and readers are waiting;
+ explicit hand-over to the readers is required.
+
+ WP (PTHREAD_RWLOCK_WRPHASE) is true if the lock is in a write phase, so
+ potentially acquired by a primary writer.
+ WL (PTHREAD_RWLOCK_WRLOCKED) is true if there is a primary writer (i.e.,
+ the thread that was able to set this bit from false to true).
+ R (all bits in __readers except the number of least-significant bits
+ denoted in PTHREAD_RWLOCK_READER_SHIFT) is the number of readers that have
+ or are trying to acquired the lock. There may be more readers waiting if
+ writers are preferred and there will be no recursive readers, in which
+ case RW (PTHREAD_RWLOCK_RWAITING) is true in state #4a.
+
+ We want to block using futexes but using __readers as a futex word directly
+ is not a good solution. First, we want to wait on different conditions
+ such as waiting for a phase change vs. waiting for the primary writer to
+ release the writer-only lock. Second, the number of readers could change
+ frequently, which would make it likely that a writer's futex_wait fails
+ frequently too because the expected value does not match the value of
+ __readers anymore.
+ Therefore, we split out the futex words into the __wrphase_futex and
+ __writers_futex fields. The former tracks the value of the WP bit and is
+ changed after changing WP by the thread that changes WP. However, because
+ of the POSIX requirements regarding mutex/rwlock destruction (i.e., that
+ destroying a rwlock is allowed as soon as no thread has acquired or will
+ acquire the lock), we have to be careful and hand over lock ownership (via
+ a phase change) carefully to those threads waiting. Specifically, we must
+ prevent a situation in which we are not quite sure whether we still have
+ to unblock another thread through a change to memory (executing a
+ futex_wake on a former futex word that is now used for something else is
+ fine).
+ The scheme we use for __wrphase_futex is that waiting threads that may
+ use the futex word to block now all have to use the futex word to block; it
+ is not allowed to take the short-cut and spin-wait on __readers because
+ then the waking thread cannot just make one final change to memory to
+ unblock all potentially waiting threads. If, for example, a reader
+ increments R in states #7 or #8, it has to then block until __wrphase_futex
+ is 0 and it can confirm that the value of 0 was stored by the primary
+ writer; in turn, the primary writer has to change to a read phase too when
+ releasing WL (i.e., to state #2), and it must change __wrphase_futex to 0
+ as the next step. This ensures that the waiting reader will not be able to
+ acquire, release, and then destroy the lock concurrently with the pending
+ futex unblock operations by the former primary writer. This scheme is
+ called explicit hand-over in what follows.
+ Note that waiting threads can cancel waiting only if explicit hand-over has
+ not yet started (e.g., if __readers is still in states #7 or #8 in the
+ example above).
+
+ Writers determine the primary writer through WL. Blocking using futexes
+ is performed using __writers_futex as a futex word; primary writers will
+ enable waiting on this futex by setting it to 1 after they acquired the WL
+ bit and will disable waiting by setting it to 0 before they release WL.
+ This leaves small windows where blocking using futexes is not possible
+ although a primary writer exists, but in turn decreases complexity of the
+ writer--writer synchronization and does not affect correctness.
+ If writers are preferred, writers can hand over WL directly to other
+ waiting writers that registered by incrementing __writers: If the primary
+ writer can CAS __writers from a non-zero value to the same value with the
+ PTHREAD_RWLOCK_WRHANDOVER bit set, it effectively transfers WL ownership
+ to one of the registered waiting writers and does not reset WL; in turn,
+ a registered writer that can clear PTHREAD_RWLOCK_WRHANDOVER using a CAS
+ then takes over WL. Note that registered waiting writers can cancel
+ waiting by decrementing __writers, but the last writer to unregister must
+ become the primary writer if PTHREAD_RWLOCK_WRHANDOVER is sedt.
+ Also note that adding another state/bit to signal potential writer--writer
+ contention (e.g., as done in the normal mutex algorithm) would not be
+ helpful because we would have to conservatively assume that there is in
+ fact no other writer, and wake up readers too.
+
+ To avoid having to call futex_wake when no thread uses __wrphase_futex or
+ __writers_futex, threads will set the PTHREAD_RWLOCK_FUTEX_USED bit in the
+ respective futex words before waiting on it (using a CAS so it will only be
+ set if in a state in which waiting would be possible). In the case of
+ __writers_futex, we wake only one thread but several threads may share
+ PTHREAD_RWLOCK_FUTEX_USED, so we must assume that there are still others.
+ This is similar to what we do in pthread_mutex_lock. We do not need to
+ do this for __wrphase_futex because there, we always wake all waiting
+ threads.
+
+ Blocking in the state #4a simply uses __readers as futex word. This
+ simplifies the algorithm but suffers from some of the drawbacks discussed
+ before, though not to the same extent because R can only decrease in this
+ state, so the number of potentially failing futex_wait attempts will be
+ bounded. All threads moving from state #4a to another state must wake
+ up threads blocked on the __readers futex.
+
+ The ordering invariants that we have to take care of in the implementation
+ are primarily those necessary for a reader--writer lock; this is rather
+ straightforward and happens during write/read phase switching (potentially
+ through explicit hand-over), and between writers through synchronization
+ involving the PTHREAD_RWLOCK_WRLOCKED or PTHREAD_RWLOCK_WRHANDOVER bits.
+ Additionally, we need to take care that modifications of __writers_futex
+ and __wrphase_futex (e.g., by otherwise unordered readers) take place in
+ the writer critical sections or read/write phases, respectively, and that
+ explicit hand-over observes stores from the previous phase. How this is
+ done is explained in more detail in comments in the code.
+
+ Many of the accesses to the futex words just need relaxed MO. This is
+ possible because we essentially drive both the core rwlock synchronization
+ and the futex synchronization in parallel. For example, an unlock will
+ unlock the rwlock and take part in the futex synchronization (using
+ PTHREAD_RWLOCK_FUTEX_USED, see above); even if they are not tightly
+ ordered in some way, the futex synchronization ensures that there are no
+ lost wake-ups, and woken threads will then eventually see the most recent
+ state of the rwlock. IOW, waiting threads will always be woken up, while
+ not being able to wait using futexes (which can happen) is harmless; in
+ turn, this means that waiting threads don't need special ordering wrt.
+ waking threads.
+
+ The futex synchronization consists of the three-state futex word:
+ (1) cannot block on it, (2) can block on it, and (3) there might be a
+ thread blocked on it (i.e., with PTHREAD_RWLOCK_FUTEX_USED set).
+ Relaxed-MO atomic read-modify-write operations are sufficient to maintain
+ this (e.g., using a CAS to go from (2) to (3) but not from (1) to (3)),
+ but we need ordering of the futex word modifications by the waking threads
+ so that they collectively make correct state changes between (1)-(3).
+ The futex-internal synchronization (i.e., the conceptual critical sections
+ around futex operations in the kernel) then ensures that even an
+ unconstrained load (i.e., relaxed MO) inside of futex_wait will not lead to
+ lost wake-ups because either the waiting thread will see the change from
+ (3) to (1) when a futex_wake came first, or this futex_wake will wake this
+ waiting thread because the waiting thread came first.
+
+
+ POSIX allows but does not require rwlock acquisitions to be a cancellation
+ point. We do not support cancellation.
+
+ TODO We do not try to elide any read or write lock acquisitions currently.
+ While this would be possible, it is unclear whether HTM performance is
+ currently predictable enough and our runtime tuning is good enough at
+ deciding when to use elision so that enabling it would lead to consistently
+ better performance. */
+
+
+static int
+__pthread_rwlock_get_private (pthread_rwlock_t *rwlock)
+{
+ return rwlock->__data.__shared != 0 ? FUTEX_SHARED : FUTEX_PRIVATE;
+}
+
+static __always_inline void
+__pthread_rwlock_rdunlock (pthread_rwlock_t *rwlock)
+{
+ int private = __pthread_rwlock_get_private (rwlock);
+ /* We decrease the number of readers, and if we are the last reader and
+ there is a primary writer, we start a write phase. We use a CAS to
+ make this atomic so that it is clear whether we must hand over ownership
+ explicitly. */
+ unsigned int r = atomic_load_relaxed (&rwlock->__data.__readers);
+ unsigned int rnew;
+ for (;;)
+ {
+ rnew = r - (1 << PTHREAD_RWLOCK_READER_SHIFT);
+ /* If we are the last reader, we also need to unblock any readers
+ that are waiting for a writer to go first (PTHREAD_RWLOCK_RWAITING)
+ so that they can register while the writer is active. */
+ if ((rnew >> PTHREAD_RWLOCK_READER_SHIFT) == 0)
+ {
+ if ((rnew & PTHREAD_RWLOCK_WRLOCKED) != 0)
+ rnew |= PTHREAD_RWLOCK_WRPHASE;
+ rnew &= ~(unsigned int) PTHREAD_RWLOCK_RWAITING;
+ }
+ /* We need release MO here for three reasons. First, so that we
+ synchronize with subsequent writers. Second, we might have been the
+ first reader and set __wrphase_futex to 0, so we need to synchronize
+ with the last reader that will set it to 1 (note that we will always
+ change __readers before the last reader, or we are the last reader).
+ Third, a writer that takes part in explicit hand-over needs to see
+ the first reader's store to __wrphase_futex (or a later value) if
+ the writer observes that a write phase has been started. */
+ if (atomic_compare_exchange_weak_release (&rwlock->__data.__readers,
+ &r, rnew))
+ break;
+ /* TODO Back-off. */
+ }
+ if ((rnew & PTHREAD_RWLOCK_WRPHASE) != 0)
+ {
+ /* We need to do explicit hand-over. We need the acquire MO fence so
+ that our modification of _wrphase_futex happens after a store by
+ another reader that started a read phase. Relaxed MO is sufficient
+ for the modification of __wrphase_futex because it is just used
+ to delay acquisition by a writer until all threads are unblocked
+ irrespective of whether they are looking at __readers or
+ __wrphase_futex; any other synchronizes-with relations that are
+ necessary are established through __readers. */
+ atomic_thread_fence_acquire ();
+ if ((atomic_exchange_relaxed (&rwlock->__data.__wrphase_futex, 1)
+ & PTHREAD_RWLOCK_FUTEX_USED) != 0)
+ futex_wake (&rwlock->__data.__wrphase_futex, INT_MAX, private);
+ }
+ /* Also wake up waiting readers if we did reset the RWAITING flag. */
+ if ((r & PTHREAD_RWLOCK_RWAITING) != (rnew & PTHREAD_RWLOCK_RWAITING))
+ futex_wake (&rwlock->__data.__readers, INT_MAX, private);
+}
+
+
+static __always_inline int
+__pthread_rwlock_rdlock_full (pthread_rwlock_t *rwlock,
+ const struct timespec *abstime)
+{
+ unsigned int r;
+
+ /* Make sure we are not holding the rwlock as a writer. This is a deadlock
+ situation we recognize and report. */
+ if (__glibc_unlikely (atomic_load_relaxed (&rwlock->__data.__cur_writer)
+ == THREAD_GETMEM (THREAD_SELF, tid)))
+ return EDEADLK;
+
+ /* If we prefer writers, recursive rdlock is disallowed, we are in a read
+ phase, and there are other readers present, we try to wait without
+ extending the read phase. We will be unblocked by either one of the
+ other active readers, or if the writer gives up WRLOCKED (e.g., on
+ timeout).
+ If there are no other readers, we simply race with any existing primary
+ writer; it would have been a race anyway, and changing the odds slightly
+ will likely not make a big difference. */
+ if (rwlock->__data.__flags == PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP)
+ {
+ r = atomic_load_relaxed (&rwlock->__data.__readers);
+ while (((r & PTHREAD_RWLOCK_WRPHASE) == 0)
+ && ((r & PTHREAD_RWLOCK_WRLOCKED) != 0)
+ && ((r >> PTHREAD_RWLOCK_READER_SHIFT) > 0))
+ {
+ /* TODO Spin first. */
+ /* Try setting the flag signaling that we are waiting without having
+ incremented the number of readers. Relaxed MO is fine because
+ this is just about waiting for a state change in __readers. */
+ if (atomic_compare_exchange_weak_relaxed
+ (&rwlock->__data.__readers, &r, r | PTHREAD_RWLOCK_RWAITING))
+ {
+ /* Wait for as long as the flag is set. An ABA situation is
+ harmless because the flag is just about the state of
+ __readers, and all threads set the flag under the same
+ conditions. */
+ while ((atomic_load_relaxed (&rwlock->__data.__readers)
+ & PTHREAD_RWLOCK_RWAITING) != 0)
+ {
+ int private = __pthread_rwlock_get_private (rwlock);
+ int err = futex_abstimed_wait (&rwlock->__data.__readers,
+ r, abstime, private);
+ /* We ignore EAGAIN and EINTR. On time-outs, we can just
+ return because we don't need to clean up anything. */
+ if (err == ETIMEDOUT)
+ return err;
+ }
+ /* It makes sense to not break out of the outer loop here
+ because we might be in the same situation again. */
+ }
+ else
+ {
+ /* TODO Back-off. */
+ }
+ }
+ }
+ /* Register as a reader, using an add-and-fetch so that R can be used as
+ expected value for future operations. Acquire MO so we synchronize with
+ prior writers as well as the last reader of the previous read phase (see
+ below). */
+ r = atomic_fetch_add_acquire (&rwlock->__data.__readers,
+ (1 << PTHREAD_RWLOCK_READER_SHIFT)) + (1 << PTHREAD_RWLOCK_READER_SHIFT);
+
+ /* Check whether there is an overflow in the number of readers. We assume
+ that the total number of threads is less than half the maximum number
+ of readers that we have bits for in __readers (i.e., with 32-bit int and
+ PTHREAD_RWLOCK_READER_SHIFT of 3, we assume there are less than
+ 1 << (32-3-1) concurrent threads).
+ If there is an overflow, we use a CAS to try to decrement the number of
+ readers if there still is an overflow situation. If so, we return
+ EAGAIN; if not, we are not a thread causing an overflow situation, and so
+ we just continue. Using a fetch-add instead of the CAS isn't possible
+ because other readers might release the lock concurrently, which could
+ make us the last reader and thus responsible for handing ownership over
+ to writers (which requires a CAS too to make the decrement and ownership
+ transfer indivisible). */
+ while (__glibc_unlikely (r >= PTHREAD_RWLOCK_READER_OVERFLOW))
+ {
+ /* Relaxed MO is okay because we just want to undo our registration and
+ cannot have changed the rwlock state substantially if the CAS
+ succeeds. */
+ if (atomic_compare_exchange_weak_relaxed (&rwlock->__data.__readers, &r,
+ r - (1 << PTHREAD_RWLOCK_READER_SHIFT)))
+ return EAGAIN;
+ }
+
+ /* We have registered as a reader, so if we are in a read phase, we have
+ acquired a read lock. This is also the reader--reader fast-path.
+ Even if there is a primary writer, we just return. If writers are to
+ be preferred and we are the only active reader, we could try to enter a
+ write phase to let the writer proceed. This would be okay because we
+ cannot have acquired the lock previously as a reader (which could result
+ in deadlock if we would wait for the primary writer to run). However,
+ this seems to be a corner case and handling it specially not be worth the
+ complexity. */
+ if (__glibc_likely ((r & PTHREAD_RWLOCK_WRPHASE) == 0))
+ return 0;
+
+ /* If there is no primary writer but we are in a write phase, we can try
+ to install a read phase ourself. */
+ while (((r & PTHREAD_RWLOCK_WRPHASE) != 0)
+ && ((r & PTHREAD_RWLOCK_WRLOCKED) == 0))
+ {
+ /* Try to enter a read phase: If the CAS below succeeds, we have
+ ownership; if it fails, we will simply retry and reassess the
+ situation.
+ Acquire MO so we synchronize with prior writers. */
+ if (atomic_compare_exchange_weak_acquire (&rwlock->__data.__readers, &r,
+ r ^ PTHREAD_RWLOCK_WRPHASE))
+ {
+ /* We started the read phase, so we are also responsible for
+ updating the write-phase futex. Relaxed MO is sufficient.
+ Note that there can be no other reader that we have to wake
+ because all other readers will see the read phase started by us
+ (or they will try to start it themselves); if a writer started
+ the read phase, we cannot have started it. Furthermore, we
+ cannot discard a PTHREAD_RWLOCK_FUTEX_USED flag because we will
+ overwrite the value set by the most recent writer (or the readers
+ before it in case of explicit hand-over) and we know that there
+ are no waiting readers. */
+ atomic_store_relaxed (&rwlock->__data.__wrphase_futex, 0);
+ return 0;
+ }
+ else
+ {
+ /* TODO Back off before retrying. Also see above. */
+ }
+ }
+
+ if ((r & PTHREAD_RWLOCK_WRPHASE) != 0)
+ {
+ /* We are in a write phase, and there must be a primary writer because
+ of the previous loop. Block until the primary writer gives up the
+ write phase. This case requires explicit hand-over using
+ __wrphase_futex.
+ However, __wrphase_futex might not have been set to 1 yet (either
+ because explicit hand-over to the writer is still ongoing, or because
+ the writer has started the write phase but does not yet have updated
+ __wrphase_futex). The least recent value of __wrphase_futex we can
+ read from here is the modification of the last read phase (because
+ we synchronize with the last reader in this read phase through
+ __readers; see the use of acquire MO on the fetch_add above).
+ Therefore, if we observe a value of 0 for __wrphase_futex, we need
+ to subsequently check that __readers now indicates a read phase; we
+ need to use acquire MO for this so that if we observe a read phase,
+ we will also see the modification of __wrphase_futex by the previous
+ writer. We then need to load __wrphase_futex again and continue to
+ wait if it is not 0, so that we do not skip explicit hand-over.
+ Relaxed MO is sufficient for the load from __wrphase_futex because
+ we just use it as an indicator for when we can proceed; we use
+ __readers and the acquire MO accesses to it to eventually read from
+ the proper stores to __wrphase_futex. */
+ unsigned int wpf;
+ bool ready = false;
+ for (;;)
+ {
+ while (((wpf = atomic_load_relaxed (&rwlock->__data.__wrphase_futex))
+ | PTHREAD_RWLOCK_FUTEX_USED) == (1 | PTHREAD_RWLOCK_FUTEX_USED))
+ {
+ int private = __pthread_rwlock_get_private (rwlock);
+ if (((wpf & PTHREAD_RWLOCK_FUTEX_USED) == 0)
+ && !atomic_compare_exchange_weak_relaxed
+ (&rwlock->__data.__wrphase_futex,
+ &wpf, wpf | PTHREAD_RWLOCK_FUTEX_USED))
+ continue;
+ int err = futex_abstimed_wait (&rwlock->__data.__wrphase_futex,
+ 1 | PTHREAD_RWLOCK_FUTEX_USED, abstime, private);
+ if (err == ETIMEDOUT)
+ {
+ /* If we timed out, we need to unregister. If no read phase
+ has been installed while we waited, we can just decrement
+ the number of readers. Otherwise, we just acquire the
+ lock, which is allowed because we give no precise timing
+ guarantees, and because the timeout is only required to
+ be in effect if we would have had to wait for other
+ threads (e.g., if futex_wait would time-out immediately
+ because the given absolute time is in the past). */
+ r = atomic_load_relaxed (&rwlock->__data.__readers);
+ while ((r & PTHREAD_RWLOCK_WRPHASE) != 0)
+ {
+ /* We don't need to make anything else visible to
+ others besides unregistering, so relaxed MO is
+ sufficient. */
+ if (atomic_compare_exchange_weak_relaxed
+ (&rwlock->__data.__readers, &r,
+ r - (1 << PTHREAD_RWLOCK_READER_SHIFT)))
+ return ETIMEDOUT;
+ /* TODO Back-off. */
+ }
+ /* Use the acquire MO fence to mirror the steps taken in the
+ non-timeout case. Note that the read can happen both
+ in the atomic_load above as well as in the failure case
+ of the CAS operation. */
+ atomic_thread_fence_acquire ();
+ /* We still need to wait for explicit hand-over, but we must
+ not use futex_wait anymore because we would just time out
+ in this case and thus make the spin-waiting we need
+ unnecessarily expensive. */
+ while ((atomic_load_relaxed (&rwlock->__data.__wrphase_futex)
+ | PTHREAD_RWLOCK_FUTEX_USED)
+ == (1 | PTHREAD_RWLOCK_FUTEX_USED))
+ {
+ /* TODO Back-off? */
+ }
+ ready = true;
+ break;
+ }
+ /* If we got interrupted (EINTR) or the futex word does not have the
+ expected value (EAGAIN), retry. */
+ }
+ if (ready)
+ /* See below. */
+ break;
+ /* We need acquire MO here so that we synchronize with the lock
+ release of the writer, and so that we observe a recent value of
+ __wrphase_futex (see below). */
+ if ((atomic_load_acquire (&rwlock->__data.__readers)
+ & PTHREAD_RWLOCK_WRPHASE) == 0)
+ /* We are in a read phase now, so the least recent modification of
+ __wrphase_futex we can read from is the store by the writer
+ with value 1. Thus, only now we can assume that if we observe
+ a value of 0, explicit hand-over is finished. Retry the loop
+ above one more time. */
+ ready = true;
+ }
+ }
+
+ return 0;
+}
+
+
+static __always_inline void
+__pthread_rwlock_wrunlock (pthread_rwlock_t *rwlock)
+{
+ int private = __pthread_rwlock_get_private (rwlock);
+
+ atomic_store_relaxed (&rwlock->__data.__cur_writer, 0);
+ /* Disable waiting by writers. We will wake up after we decided how to
+ proceed. */
+ bool wake_writers = ((atomic_exchange_relaxed
+ (&rwlock->__data.__writers_futex, 0) & PTHREAD_RWLOCK_FUTEX_USED) != 0);
+
+ if (rwlock->__data.__flags != PTHREAD_RWLOCK_PREFER_READER_NP)
+ {
+ /* First, try to hand over to another writer. */
+ unsigned int w = atomic_load_relaxed (&rwlock->__data.__writers);
+ while (w != 0)
+ {
+ /* Release MO so that another writer that gets WRLOCKED from us will
+ synchronize with us and thus can take over our view of
+ __readers (including, for example, whether we are in a write
+ phase or not). */
+ if (atomic_compare_exchange_weak_release (&rwlock->__data.__writers,
+ &w, w | PTHREAD_RWLOCK_WRHANDOVER))
+ /* Another writer will take over. */
+ goto done;
+ /* TODO Back-off. */
+ }
+ }
+
+ /* We have done everything we needed to do to prefer writers, so now we
+ either hand over explicitly to readers if there are any, or we simply
+ stay in a write phase. See pthread_rwlock_rdunlock for more details. */
+ unsigned int r = atomic_load_relaxed (&rwlock->__data.__readers);
+ /* Release MO so that subsequent readers or writers synchronize with us. */
+ while (!atomic_compare_exchange_weak_release
+ (&rwlock->__data.__readers, &r, (r ^ PTHREAD_RWLOCK_WRLOCKED)
+ ^ ((r >> PTHREAD_RWLOCK_READER_SHIFT) == 0 ? 0
+ : PTHREAD_RWLOCK_WRPHASE)))
+ {
+ /* TODO Back-off. */
+ }
+ if ((r >> PTHREAD_RWLOCK_READER_SHIFT) != 0)
+ {
+ /* We must hand over explicitly through __wrphase_futex. Relaxed MO is
+ sufficient because it is just used to delay acquisition by a writer;
+ any other synchronizes-with relations that are necessary are
+ established through __readers. */
+ if ((atomic_exchange_relaxed (&rwlock->__data.__wrphase_futex, 0)
+ & PTHREAD_RWLOCK_FUTEX_USED) != 0)
+ futex_wake (&rwlock->__data.__wrphase_futex, INT_MAX, private);
+ }
+
+ done:
+ /* We released WRLOCKED in some way, so wake a writer. */
+ if (wake_writers)
+ futex_wake (&rwlock->__data.__writers_futex, 1, private);
+}
+
+
+static __always_inline int
+__pthread_rwlock_wrlock_full (pthread_rwlock_t *rwlock,
+ const struct timespec *abstime)
+{
+ /* Make sure we are not holding the rwlock as a writer. This is a deadlock
+ situation we recognize and report. */
+ if (__glibc_unlikely (atomic_load_relaxed (&rwlock->__data.__cur_writer)
+ == THREAD_GETMEM (THREAD_SELF, tid)))
+ return EDEADLK;
+
+ /* First we try to acquire the role of primary writer by setting WRLOCKED;
+ if it was set before, there already is a primary writer. Acquire MO so
+ that we synchronize with previous primary writers.
+
+ We do not try to change to a write phase right away using a fetch_or
+ because we would have to reset it again and wake readers if there are
+ readers present (some readers could try to acquire the lock more than
+ once, so setting a write phase in the middle of this could cause
+ deadlock). Changing to a write phase eagerly would only speed up the
+ transition from a read phase to a write phase in the uncontended case,
+ but it would slow down the contended case if readers are preferred (which
+ is the default).
+ We could try to CAS from a state with no readers to a write phase, but
+ this could be less scalable if readers arrive and leave frequently. */
+ bool may_share_futex_used_flag = false;
+ unsigned int r = atomic_fetch_or_acquire (&rwlock->__data.__readers,
+ PTHREAD_RWLOCK_WRLOCKED);
+ if (__glibc_unlikely ((r & PTHREAD_RWLOCK_WRLOCKED) != 0))
+ {
+ /* There is another primary writer. */
+ bool prefer_writer =
+ (rwlock->__data.__flags != PTHREAD_RWLOCK_PREFER_READER_NP);
+ if (prefer_writer)
+ {
+ /* We register as a waiting writer, so that we can make use of
+ writer--writer hand-over. Relaxed MO is fine because we just
+ want to register. We assume that the maximum number of threads
+ is less than the capacity in __writers. */
+ atomic_fetch_add_relaxed (&rwlock->__data.__writers, 1);
+ }
+ for (;;)
+ {
+ /* TODO Spin until WRLOCKED is 0 before trying the CAS below.
+ But pay attention to not delay trying writer--writer hand-over
+ for too long (which we must try eventually anyway). */
+ if ((r & PTHREAD_RWLOCK_WRLOCKED) == 0)
+ {
+ /* Try to become the primary writer or retry. Acquire MO as in
+ the fetch_or above. */
+ if (atomic_compare_exchange_weak_acquire
+ (&rwlock->__data.__readers, &r,
+ r | PTHREAD_RWLOCK_WRLOCKED))
+ {
+ if (prefer_writer)
+ {
+ /* Unregister as a waiting writer. Note that because we
+ acquired WRLOCKED, WRHANDOVER will not be set.
+ Acquire MO on the CAS above ensures that
+ unregistering happens after the previous writer;
+ this sorts the accesses to __writers by all
+ primary writers in a useful way (e.g., any other
+ primary writer acquiring after us or getting it from
+ us through WRHANDOVER will see both our changes to
+ __writers).
+ ??? Perhaps this is not strictly necessary for
+ reasons we do not yet know of. */
+ atomic_fetch_add_relaxed (&rwlock->__data.__writers,
+ -1);
+ }
+ break;
+ }
+ /* Retry if the CAS fails (r will have been updated). */
+ continue;
+ }
+ /* If writer--writer hand-over is available, try to become the
+ primary writer this way by grabbing the WRHANDOVER token. If we
+ succeed, we own WRLOCKED. */
+ if (prefer_writer)
+ {
+ unsigned int w = atomic_load_relaxed
+ (&rwlock->__data.__writers);
+ if ((w & PTHREAD_RWLOCK_WRHANDOVER) != 0)
+ {
+ /* Acquire MO is required here so that we synchronize with
+ the writer that handed over WRLOCKED. We also need this
+ for the reload of __readers below because our view of
+ __readers must be at least as recent as the view of the
+ writer that handed over WRLOCKED; we must avoid an ABA
+ through WRHANDOVER, which could, for example, lead to us
+ assuming we are still in a write phase when in fact we
+ are not. */
+ if (atomic_compare_exchange_weak_acquire
+ (&rwlock->__data.__writers,
+ &w, (w - PTHREAD_RWLOCK_WRHANDOVER - 1)))
+ {
+ /* Reload so our view is consistent with the view of
+ the previous owner of WRLOCKED. See above. */
+ r = atomic_load_relaxed (&rwlock->__data.__readers);
+ break;
+ }
+ continue;
+ }
+ }
+ /* We did not acquire WRLOCKED nor were able to use writer--writer
+ hand-over, so we block on __writers_futex. */
+ int private = __pthread_rwlock_get_private (rwlock);
+ unsigned int wf = atomic_load_relaxed
+ (&rwlock->__data.__writers_futex);
+ if ((wf & ~(unsigned int) PTHREAD_RWLOCK_FUTEX_USED) != 1)
+ continue;
+ if ((wf != (1 | PTHREAD_RWLOCK_FUTEX_USED))
+ && !atomic_compare_exchange_weak_relaxed
+ (&rwlock->__data.__writers_futex, &wf,
+ 1 | PTHREAD_RWLOCK_FUTEX_USED))
+ continue;
+ /* We set the flag that signals that the futex is used, or we could
+ have set it if we had been faster than other waiters. As a
+ result, we may share the flag with an unknown number of other
+ writers. Therefore, we must keep this flag set when we acquire
+ the lock. We do not need to do this when we do not reach this
+ point here because then we are not part of the group that may
+ share the flag, and another writer will wake one of the writers
+ in this group. */
+ may_share_futex_used_flag = true;
+ int err = futex_abstimed_wait (&rwlock->__data.__writers_futex,
+ 1 | PTHREAD_RWLOCK_FUTEX_USED, abstime, private);
+ if (err == ETIMEDOUT)
+ {
+ if (prefer_writer)
+ {
+ /* We need to unregister as a waiting writer. If we are the
+ last writer and writer--writer hand-over is available,
+ we must make use of it because nobody else will reset
+ WRLOCKED otherwise. (If we use it, we simply pretend
+ that this happened before the timeout; see
+ pthread_rwlock_rdlock_full for the full reasoning.)
+ Also see the similar code above. */
+ unsigned int w = atomic_load_relaxed
+ (&rwlock->__data.__writers);
+ while (!atomic_compare_exchange_weak_acquire
+ (&rwlock->__data.__writers, &w,
+ (w == PTHREAD_RWLOCK_WRHANDOVER + 1 ? 0 : w - 1)))
+ {
+ /* TODO Back-off. */
+ }
+ if (w == PTHREAD_RWLOCK_WRHANDOVER + 1)
+ {
+ /* We must continue as primary writer. See above. */
+ r = atomic_load_relaxed (&rwlock->__data.__readers);
+ break;
+ }
+ }
+ /* We cleaned up and cannot have stolen another waiting writer's
+ futex wake-up, so just return. */
+ return ETIMEDOUT;
+ }
+ /* If we got interrupted (EINTR) or the futex word does not have the
+ expected value (EAGAIN), retry after reloading __readers. */
+ r = atomic_load_relaxed (&rwlock->__data.__readers);
+ }
+ /* Our snapshot of __readers is up-to-date at this point because we
+ either set WRLOCKED using a CAS or were handed over WRLOCKED from
+ another writer whose snapshot of __readers we inherit. */
+ }
+
+ /* If we are in a read phase and there are no readers, try to start a write
+ phase. */
+ while (((r & PTHREAD_RWLOCK_WRPHASE) == 0)
+ && ((r >> PTHREAD_RWLOCK_READER_SHIFT) == 0))
+ {
+ /* Acquire MO so that we synchronize with prior writers and do
+ not interfere with their updates to __writers_futex, as well
+ as regarding prior readers and their updates to __wrphase_futex,
+ respectively. */
+ if (atomic_compare_exchange_weak_acquire (&rwlock->__data.__readers,
+ &r, r | PTHREAD_RWLOCK_WRPHASE))
+ {
+ /* We have started a write phase, so need to enable readers to wait.
+ See the similar case in__pthread_rwlock_rdlock_full. */
+ atomic_store_relaxed (&rwlock->__data.__wrphase_futex, 1);
+ /* Make sure we fall through to the end of the function. */
+ r |= PTHREAD_RWLOCK_WRPHASE;
+ break;
+ }
+ /* TODO Back-off. */
+ }
+
+ /* We are the primary writer; enable blocking on __writers_futex. Relaxed
+ MO is sufficient for futex words; acquire MO on the previous
+ modifications of __readers ensures that this store happens after the
+ store of value 0 by the previous primary writer. */
+ atomic_store_relaxed (&rwlock->__data.__writers_futex,
+ 1 | (may_share_futex_used_flag ? PTHREAD_RWLOCK_FUTEX_USED : 0));
+
+ if (__glibc_unlikely ((r & PTHREAD_RWLOCK_WRPHASE) == 0))
+ {
+ /* We are not in a read phase and there are readers (because of the
+ previous loop). Thus, we have to wait for explicit hand-over from
+ one of these readers.
+ We basically do the same steps as for the similar case in
+ __pthread_rwlock_rdlock_full, except that we additionally might try
+ to directly hand over to another writer and need to wake up
+ other writers or waiting readers (i.e., PTHREAD_RWLOCK_RWAITING). */
+ unsigned int wpf;
+ bool ready = false;
+ for (;;)
+ {
+ while (((wpf = atomic_load_relaxed (&rwlock->__data.__wrphase_futex))
+ | PTHREAD_RWLOCK_FUTEX_USED) == PTHREAD_RWLOCK_FUTEX_USED)
+ {
+ int private = __pthread_rwlock_get_private (rwlock);
+ if (((wpf & PTHREAD_RWLOCK_FUTEX_USED) == 0)
+ && !atomic_compare_exchange_weak_relaxed
+ (&rwlock->__data.__wrphase_futex, &wpf,
+ PTHREAD_RWLOCK_FUTEX_USED))
+ continue;
+ int err = futex_abstimed_wait (&rwlock->__data.__wrphase_futex,
+ PTHREAD_RWLOCK_FUTEX_USED, abstime, private);
+ if (err == ETIMEDOUT)
+ {
+ if (rwlock->__data.__flags
+ != PTHREAD_RWLOCK_PREFER_READER_NP)
+ {
+ /* We try writer--writer hand-over. */
+ unsigned int w = atomic_load_relaxed
+ (&rwlock->__data.__writers);
+ if (w != 0)
+ {
+ /* We are about to hand over WRLOCKED, so we must
+ release __writers_futex too; otherwise, we'd have
+ a pending store, which could at least prevent
+ other threads from waiting using the futex
+ because it could interleave with the stores
+ by subsequent writers. In turn, this means that
+ we have to clean up when we do not hand over
+ WRLOCKED.
+ Release MO so that another writer that gets
+ WRLOCKED from us can take over our view of
+ __readers. */
+ unsigned int wf = atomic_exchange_relaxed
+ (&rwlock->__data.__writers_futex, 0);
+ while (w != 0)
+ {
+ if (atomic_compare_exchange_weak_release
+ (&rwlock->__data.__writers, &w,
+ w | PTHREAD_RWLOCK_WRHANDOVER))
+ {
+ /* Wake other writers. */
+ if ((wf & PTHREAD_RWLOCK_FUTEX_USED) != 0)
+ futex_wake
+ (&rwlock->__data.__writers_futex, 1,
+ private);
+ return ETIMEDOUT;
+ }
+ /* TODO Back-off. */
+ }
+ /* We still own WRLOCKED and someone else might set
+ a write phase concurrently, so enable waiting
+ again. Make sure we don't loose the flag that
+ signals whether there are threads waiting on
+ this futex. */
+ atomic_store_relaxed
+ (&rwlock->__data.__writers_futex, wf);
+ }
+ }
+ /* If we timed out and we are not in a write phase, we can
+ just stop being a primary writer. Otherwise, we just
+ acquire the lock. */
+ r = atomic_load_relaxed (&rwlock->__data.__readers);
+ if ((r & PTHREAD_RWLOCK_WRPHASE) == 0)
+ {
+ /* We are about to release WRLOCKED, so we must release
+ __writers_futex too; see the handling of
+ writer--writer hand-over above. */
+ unsigned int wf = atomic_exchange_relaxed
+ (&rwlock->__data.__writers_futex, 0);
+ while ((r & PTHREAD_RWLOCK_WRPHASE) == 0)
+ {
+ /* While we don't need to make anything from a
+ caller's critical section visible to other
+ threads, we need to ensure that our changes to
+ __writers_futex are properly ordered.
+ Therefore, use release MO to synchronize with
+ subsequent primary writers. Also wake up any
+ waiting readers as they are waiting because of
+ us. */
+ if (atomic_compare_exchange_weak_release
+ (&rwlock->__data.__readers, &r,
+ (r ^ PTHREAD_RWLOCK_WRLOCKED)
+ & ~(unsigned int) PTHREAD_RWLOCK_RWAITING))
+ {
+ /* Wake other writers. */
+ if ((wf & PTHREAD_RWLOCK_FUTEX_USED) != 0)
+ futex_wake (&rwlock->__data.__writers_futex,
+ 1, private);
+ /* Wake waiting readers. */
+ if ((r & PTHREAD_RWLOCK_RWAITING) != 0)
+ futex_wake (&rwlock->__data.__readers,
+ INT_MAX, private);
+ return ETIMEDOUT;
+ }
+ }
+ /* We still own WRLOCKED and someone else might set a
+ write phase concurrently, so enable waiting again.
+ Make sure we don't loose the flag that signals
+ whether there are threads waiting on this futex. */
+ atomic_store_relaxed (&rwlock->__data.__writers_futex,
+ wf);
+ }
+ /* Use the acquire MO fence to mirror the steps taken in the
+ non-timeout case. Note that the read can happen both
+ in the atomic_load above as well as in the failure case
+ of the CAS operation. */
+ atomic_thread_fence_acquire ();
+ /* We still need to wait for explicit hand-over, but we must
+ not use futex_wait anymore. */
+ while ((atomic_load_relaxed
+ (&rwlock->__data.__wrphase_futex)
+ | PTHREAD_RWLOCK_FUTEX_USED)
+ == PTHREAD_RWLOCK_FUTEX_USED)
+ {
+ /* TODO Back-off. */
+ }
+ ready = true;
+ break;
+ }
+ /* If we got interrupted (EINTR) or the futex word does not have
+ the expected value (EAGAIN), retry. */
+ }
+ /* See pthread_rwlock_rdlock_full. */
+ if (ready)
+ break;
+ if ((atomic_load_acquire (&rwlock->__data.__readers)
+ & PTHREAD_RWLOCK_WRPHASE) != 0)
+ ready = true;
+ }
+ }
+
+ atomic_store_relaxed (&rwlock->__data.__cur_writer,
+ THREAD_GETMEM (THREAD_SELF, tid));
+ return 0;
+}
@@ -18,7 +18,6 @@
#include "pthreadP.h"
#include <string.h>
-#include <kernel-features.h>
static const struct pthread_rwlockattr default_rwlockattr =
@@ -28,6 +27,7 @@ static const struct pthread_rwlockattr default_rwlockattr =
};
+/* See pthread_rwlock_common.c. */
int
__pthread_rwlock_init (pthread_rwlock_t *rwlock,
const pthread_rwlockattr_t *attr)
@@ -38,27 +38,10 @@ __pthread_rwlock_init (pthread_rwlock_t *rwlock,
memset (rwlock, '\0', sizeof (*rwlock));
- rwlock->__data.__flags
- = iattr->lockkind == PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP;
+ rwlock->__data.__flags = iattr->lockkind;
- /* The __SHARED field is computed to minimize the work that needs to
- be done while handling the futex. There are two inputs: the
- availability of private futexes and whether the rwlock is shared
- or private. Unfortunately the value of a private rwlock is
- fixed: it must be zero. The PRIVATE_FUTEX flag has the value
- 0x80 in case private futexes are available and zero otherwise.
- This leads to the following table:
-
- | pshared | result
- | shared private | shared private |
- ------------+-----------------+-----------------+
- !avail 0 | 0 0 | 0 0 |
- avail 0x80 | 0x80 0 | 0 0x80 |
-
- If the pshared value is in locking functions XORed with avail
- we get the expected result. */
- rwlock->__data.__shared = (iattr->pshared == PTHREAD_PROCESS_PRIVATE
- ? 0 : FUTEX_PRIVATE_FLAG);
+ /* The value of __SHARED in a private rwlock must be zero. */
+ rwlock->__data.__shared = (iattr->pshared != PTHREAD_PROCESS_PRIVATE);
return 0;
}
@@ -16,165 +16,17 @@
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
-#include <errno.h>
-#include <sysdep.h>
-#include <lowlevellock.h>
-#include <futex-internal.h>
-#include <pthread.h>
-#include <pthreadP.h>
-#include <stap-probe.h>
-#include <elide.h>
-#include <stdbool.h>
-
-
-/* Acquire read lock for RWLOCK. Slow path. */
-static int __attribute__((noinline))
-__pthread_rwlock_rdlock_slow (pthread_rwlock_t *rwlock)
-{
- int result = 0;
- bool wake = false;
- int futex_shared =
- rwlock->__data.__shared == LLL_PRIVATE ? FUTEX_PRIVATE : FUTEX_SHARED;
-
- /* Lock is taken in caller. */
-
- while (1)
- {
- /* Make sure we are not holding the rwlock as a writer. This is
- a deadlock situation we recognize and report. */
- if (__builtin_expect (rwlock->__data.__writer
- == THREAD_GETMEM (THREAD_SELF, tid), 0))
- {
- result = EDEADLK;
- break;
- }
-
- /* Remember that we are a reader. */
- if (__glibc_unlikely (++rwlock->__data.__nr_readers_queued == 0))
- {
- /* Overflow on number of queued readers. */
- --rwlock->__data.__nr_readers_queued;
- result = EAGAIN;
- break;
- }
-
- int waitval = rwlock->__data.__readers_wakeup;
-
- /* Free the lock. */
- lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
-
- /* Wait for the writer to finish. We do not check the return value
- because we decide how to continue based on the state of the rwlock. */
- futex_wait_simple (&rwlock->__data.__readers_wakeup, waitval,
- futex_shared);
-
- /* Get the lock. */
- lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
-
- --rwlock->__data.__nr_readers_queued;
-
- /* Get the rwlock if there is no writer... */
- if (rwlock->__data.__writer == 0
- /* ...and if either no writer is waiting or we prefer readers. */
- && (!rwlock->__data.__nr_writers_queued
- || PTHREAD_RWLOCK_PREFER_READER_P (rwlock)))
- {
- /* Increment the reader counter. Avoid overflow. */
- if (__glibc_unlikely (++rwlock->__data.__nr_readers == 0))
- {
- /* Overflow on number of readers. */
- --rwlock->__data.__nr_readers;
- result = EAGAIN;
- }
- else
- {
- LIBC_PROBE (rdlock_acquire_read, 1, rwlock);
- /* See pthread_rwlock_rdlock. */
- if (rwlock->__data.__nr_readers == 1
- && rwlock->__data.__nr_readers_queued > 0
- && rwlock->__data.__nr_writers_queued > 0)
- {
- ++rwlock->__data.__readers_wakeup;
- wake = true;
- }
- }
-
- break;
- }
- }
-
- /* We are done, free the lock. */
- lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
-
- if (wake)
- futex_wake (&rwlock->__data.__readers_wakeup, INT_MAX, futex_shared);
-
- return result;
-}
-
-
-/* Fast path of acquiring read lock on RWLOCK. */
+#include "pthread_rwlock_common.c"
+/* See pthread_rwlock_common.c. */
int
__pthread_rwlock_rdlock (pthread_rwlock_t *rwlock)
{
- int result = 0;
- bool wake = false;
- int futex_shared =
- rwlock->__data.__shared == LLL_PRIVATE ? FUTEX_PRIVATE : FUTEX_SHARED;
-
LIBC_PROBE (rdlock_entry, 1, rwlock);
- if (ELIDE_LOCK (rwlock->__data.__rwelision,
- rwlock->__data.__lock == 0
- && rwlock->__data.__writer == 0
- && rwlock->__data.__nr_readers == 0))
- return 0;
-
- /* Make sure we are alone. */
- lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
-
- /* Get the rwlock if there is no writer... */
- if (rwlock->__data.__writer == 0
- /* ...and if either no writer is waiting or we prefer readers. */
- && (!rwlock->__data.__nr_writers_queued
- || PTHREAD_RWLOCK_PREFER_READER_P (rwlock)))
- {
- /* Increment the reader counter. Avoid overflow. */
- if (__glibc_unlikely (++rwlock->__data.__nr_readers == 0))
- {
- /* Overflow on number of readers. */
- --rwlock->__data.__nr_readers;
- result = EAGAIN;
- }
- else
- {
- LIBC_PROBE (rdlock_acquire_read, 1, rwlock);
- /* If we are the first reader, and there are blocked readers and
- writers (which we don't prefer, see above), then it can be the
- case that we stole the lock from a writer that was already woken
- to acquire it. That means that we need to take over the writer's
- responsibility to wake all readers (see pthread_rwlock_unlock).
- Thus, wake all readers in this case. */
- if (rwlock->__data.__nr_readers == 1
- && rwlock->__data.__nr_readers_queued > 0
- && rwlock->__data.__nr_writers_queued > 0)
- {
- ++rwlock->__data.__readers_wakeup;
- wake = true;
- }
- }
-
- /* We are done, free the lock. */
- lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
-
- if (wake)
- futex_wake (&rwlock->__data.__readers_wakeup, INT_MAX, futex_shared);
-
- return result;
- }
-
- return __pthread_rwlock_rdlock_slow (rwlock);
+ int result = __pthread_rwlock_rdlock_full (rwlock, NULL);
+ LIBC_PROBE (rdlock_acquire_read, 1, rwlock);
+ return result;
}
weak_alias (__pthread_rwlock_rdlock, pthread_rwlock_rdlock)
@@ -16,121 +16,22 @@
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
-#include <errno.h>
-#include <sysdep.h>
-#include <lowlevellock.h>
-#include <futex-internal.h>
-#include <pthread.h>
-#include <pthreadP.h>
-#include <sys/time.h>
-#include <stdbool.h>
+#include "pthread_rwlock_common.c"
-
-/* Try to acquire read lock for RWLOCK or return after specfied time. */
+/* See pthread_rwlock_common.c. */
int
pthread_rwlock_timedrdlock (pthread_rwlock_t *rwlock,
- const struct timespec *abstime)
+ const struct timespec *abstime)
{
- int result = 0;
- bool wake = false;
- int futex_shared =
- rwlock->__data.__shared == LLL_PRIVATE ? FUTEX_PRIVATE : FUTEX_SHARED;
-
- /* Make sure we are alone. */
- lll_lock(rwlock->__data.__lock, rwlock->__data.__shared);
-
- while (1)
- {
- int err;
-
- /* Get the rwlock if there is no writer... */
- if (rwlock->__data.__writer == 0
- /* ...and if either no writer is waiting or we prefer readers. */
- && (!rwlock->__data.__nr_writers_queued
- || PTHREAD_RWLOCK_PREFER_READER_P (rwlock)))
- {
- /* Increment the reader counter. Avoid overflow. */
- if (++rwlock->__data.__nr_readers == 0)
- {
- /* Overflow on number of readers. */
- --rwlock->__data.__nr_readers;
- result = EAGAIN;
- }
- else
- {
- /* See pthread_rwlock_rdlock. */
- if (rwlock->__data.__nr_readers == 1
- && rwlock->__data.__nr_readers_queued > 0
- && rwlock->__data.__nr_writers_queued > 0)
- {
- ++rwlock->__data.__readers_wakeup;
- wake = true;
- }
- }
-
- break;
- }
-
- /* Make sure we are not holding the rwlock as a writer. This is
- a deadlock situation we recognize and report. */
- if (__builtin_expect (rwlock->__data.__writer
- == THREAD_GETMEM (THREAD_SELF, tid), 0))
- {
- result = EDEADLK;
- break;
- }
-
- /* Make sure the passed in timeout value is valid. Ideally this
- test would be executed once. But since it must not be
- performed if we would not block at all simply moving the test
- to the front is no option. Replicating all the code is
- costly while this test is not. */
- if (__builtin_expect (abstime->tv_nsec >= 1000000000
- || abstime->tv_nsec < 0, 0))
- {
- result = EINVAL;
- break;
- }
-
- /* Remember that we are a reader. */
- if (++rwlock->__data.__nr_readers_queued == 0)
- {
- /* Overflow on number of queued readers. */
- --rwlock->__data.__nr_readers_queued;
- result = EAGAIN;
- break;
- }
-
- int waitval = rwlock->__data.__readers_wakeup;
-
- /* Free the lock. */
- lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
-
- /* Wait for the writer to finish. We handle ETIMEDOUT below; on other
- return values, we decide how to continue based on the state of the
- rwlock. */
- err = futex_abstimed_wait (&rwlock->__data.__readers_wakeup, waitval,
- abstime, futex_shared);
-
- /* Get the lock. */
- lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
-
- --rwlock->__data.__nr_readers_queued;
-
- /* Did the futex call time out? */
- if (err == ETIMEDOUT)
- {
- /* Yep, report it. */
- result = ETIMEDOUT;
- break;
- }
- }
-
- /* We are done, free the lock. */
- lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
-
- if (wake)
- futex_wake (&rwlock->__data.__readers_wakeup, INT_MAX, futex_shared);
-
- return result;
+ /* Make sure the passed in timeout value is valid. Note that the previous
+ implementation assumed that this check *must* not be performed if there
+ would in fact be no blocking; however, POSIX only requires that "the
+ validity of the abstime parameter need not be checked if the lock can be
+ immediately acquired" (i.e., we need not but may check it). */
+ /* ??? Just move this to __pthread_rwlock_rdlock_full? */
+ if (__glibc_unlikely (abstime->tv_nsec >= 1000000000
+ || abstime->tv_nsec < 0))
+ return EINVAL;
+
+ return __pthread_rwlock_rdlock_full (rwlock, abstime);
}
@@ -16,121 +16,22 @@
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
-#include <errno.h>
-#include <sysdep.h>
-#include <lowlevellock.h>
-#include <futex-internal.h>
-#include <pthread.h>
-#include <pthreadP.h>
-#include <sys/time.h>
-#include <stdbool.h>
+#include "pthread_rwlock_common.c"
-
-/* Try to acquire write lock for RWLOCK or return after specfied time. */
+/* See pthread_rwlock_common.c. */
int
pthread_rwlock_timedwrlock (pthread_rwlock_t *rwlock,
- const struct timespec *abstime)
+ const struct timespec *abstime)
{
- int result = 0;
- bool wake_readers = false;
- int futex_shared =
- rwlock->__data.__shared == LLL_PRIVATE ? FUTEX_PRIVATE : FUTEX_SHARED;
-
- /* Make sure we are alone. */
- lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
-
- while (1)
- {
- int err;
-
- /* Get the rwlock if there is no writer and no reader. */
- if (rwlock->__data.__writer == 0 && rwlock->__data.__nr_readers == 0)
- {
- /* Mark self as writer. */
- rwlock->__data.__writer = THREAD_GETMEM (THREAD_SELF, tid);
- break;
- }
-
- /* Make sure we are not holding the rwlock as a writer. This is
- a deadlock situation we recognize and report. */
- if (__builtin_expect (rwlock->__data.__writer
- == THREAD_GETMEM (THREAD_SELF, tid), 0))
- {
- result = EDEADLK;
- break;
- }
-
- /* Make sure the passed in timeout value is valid. Ideally this
- test would be executed once. But since it must not be
- performed if we would not block at all simply moving the test
- to the front is no option. Replicating all the code is
- costly while this test is not. */
- if (__builtin_expect (abstime->tv_nsec >= 1000000000
- || abstime->tv_nsec < 0, 0))
- {
- result = EINVAL;
- break;
- }
-
- /* Remember that we are a writer. */
- if (++rwlock->__data.__nr_writers_queued == 0)
- {
- /* Overflow on number of queued writers. */
- --rwlock->__data.__nr_writers_queued;
- result = EAGAIN;
- break;
- }
-
- int waitval = rwlock->__data.__writer_wakeup;
-
- /* Free the lock. */
- lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
-
- /* Wait for the writer or reader(s) to finish. We handle ETIMEDOUT
- below; on other return values, we decide how to continue based on
- the state of the rwlock. */
- err = futex_abstimed_wait (&rwlock->__data.__writer_wakeup, waitval,
- abstime, futex_shared);
-
- /* Get the lock. */
- lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
-
- /* To start over again, remove the thread from the writer list. */
- --rwlock->__data.__nr_writers_queued;
-
- /* Did the futex call time out? */
- if (err == ETIMEDOUT)
- {
- result = ETIMEDOUT;
- /* If we prefer writers, it can have happened that readers blocked
- for us to acquire the lock first. If we have timed out, we need
- to wake such readers if there are any, and if there is no writer
- currently (otherwise, the writer will take care of wake-up).
- Likewise, even if we prefer readers, we can be responsible for
- wake-up (see pthread_rwlock_unlock) if no reader or writer has
- acquired the lock. We have timed out and thus not consumed a
- futex wake-up; therefore, if there is no other blocked writer
- that would consume the wake-up and thus take over responsibility,
- we need to wake blocked readers. */
- if ((!PTHREAD_RWLOCK_PREFER_READER_P (rwlock)
- || ((rwlock->__data.__nr_readers == 0)
- && (rwlock->__data.__nr_writers_queued == 0)))
- && (rwlock->__data.__nr_readers_queued > 0)
- && (rwlock->__data.__writer == 0))
- {
- ++rwlock->__data.__readers_wakeup;
- wake_readers = true;
- }
- break;
- }
- }
-
- /* We are done, free the lock. */
- lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
-
- /* Might be required after timeouts. */
- if (wake_readers)
- futex_wake (&rwlock->__data.__readers_wakeup, INT_MAX, futex_shared);
-
- return result;
+ /* Make sure the passed in timeout value is valid. Note that the previous
+ implementation assumed that this check *must* not be performed if there
+ would in fact be no blocking; however, POSIX only requires that "the
+ validity of the abstime parameter need not be checked if the lock can be
+ immediately acquired" (i.e., we need not but may check it). */
+ /* ??? Just move this to __pthread_rwlock_wrlock_full? */
+ if (__glibc_unlikely (abstime->tv_nsec >= 1000000000
+ || abstime->tv_nsec < 0))
+ return EINVAL;
+
+ return __pthread_rwlock_wrlock_full (rwlock, abstime);
}
@@ -18,56 +18,86 @@
#include <errno.h>
#include "pthreadP.h"
-#include <lowlevellock.h>
-#include <futex-internal.h>
-#include <elide.h>
+#include <atomic.h>
#include <stdbool.h>
+#include "pthread_rwlock_common.c"
+/* See pthread_rwlock_common.c for an overview. */
int
__pthread_rwlock_tryrdlock (pthread_rwlock_t *rwlock)
{
- int result = EBUSY;
- bool wake = false;
- int futex_shared =
- rwlock->__data.__shared == LLL_PRIVATE ? FUTEX_PRIVATE : FUTEX_SHARED;
-
- if (ELIDE_TRYLOCK (rwlock->__data.__rwelision,
- rwlock->__data.__lock == 0
- && rwlock->__data.__nr_readers == 0
- && rwlock->__data.__writer, 0))
- return 0;
-
- lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
-
- if (rwlock->__data.__writer == 0
- && (rwlock->__data.__nr_writers_queued == 0
- || PTHREAD_RWLOCK_PREFER_READER_P (rwlock)))
+ /* For tryrdlock, we could speculate that we will succeed and go ahead and
+ register as a reader. However, if we misspeculate, we have to do the
+ same steps as a timed-out rdlock, which will increase contention.
+ Therefore, there is a trade-off between being able to use a combinable
+ read-modify-write operation and a CAS loop as used below; we pick the
+ latter because it simplifies the code, and should perform better when
+ tryrdlock is used in cases where writers are infrequent.
+ Because POSIX does not require a failed trylock to "synchronize memory",
+ relaxed MO is sufficient here and on the failure path of the CAS
+ below. */
+ unsigned int r = atomic_load_relaxed (&rwlock->__data.__readers);
+ unsigned int rnew;
+ do
{
- if (__glibc_unlikely (++rwlock->__data.__nr_readers == 0))
+ if ((r & PTHREAD_RWLOCK_WRPHASE) == 0)
{
- --rwlock->__data.__nr_readers;
- result = EAGAIN;
+ /* If we are in a read phase, try to acquire unless there is a
+ primary writer and we prefer writers and there will be no
+ recursive read locks. */
+ if (((r & PTHREAD_RWLOCK_WRLOCKED) != 0)
+ && (rwlock->__data.__flags
+ == PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP))
+ return EBUSY;
+ rnew = r + (1 << PTHREAD_RWLOCK_READER_SHIFT);
+ /* If we could have caused an overflow or take effect during an
+ overflow, we just can / need to return EAGAIN. There is no need
+ to have modified the number of readers because we could have
+ done that and cleaned up immediately. */
+ if (rnew >= PTHREAD_RWLOCK_READER_OVERFLOW)
+ return EAGAIN;
}
else
{
- result = 0;
- /* See pthread_rwlock_rdlock. */
- if (rwlock->__data.__nr_readers == 1
- && rwlock->__data.__nr_readers_queued > 0
- && rwlock->__data.__nr_writers_queued > 0)
+ /* If there is a writer that has acquired the lock and we are in
+ a write phase, fail. */
+ if ((r & PTHREAD_RWLOCK_WRLOCKED) != 0)
+ return EBUSY;
+ else
{
- ++rwlock->__data.__readers_wakeup;
- wake = true;
+ /* If we do not care about potentially waiting writers, just
+ try to acquire. */
+ rnew = (r + (1 << PTHREAD_RWLOCK_READER_SHIFT))
+ ^ PTHREAD_RWLOCK_WRPHASE;
}
}
}
+ /* If the CAS fails, we retry; this prevents that tryrdlock fails spuriously
+ (i.e., fails to acquire the lock although there is no writer), which is
+ fine for C++14 but not currently allowed by POSIX.
+ However, because tryrdlock must not appear to block, we should avoid
+ starving this CAS loop due to constant changes to __readers:
+ While normal rdlock readers that won't be able to acquire will just block
+ (and we expect timeouts on timedrdlock to be longer than one retry of the
+ CAS loop), we can have concurrently failing tryrdlock calls due to
+ readers or writers that acquire and release in the meantime. Using
+ randomized exponential back-off to make a live-lock unlikely should be
+ sufficient.
+ Acquire MO so we synchronize with prior writers. */
+ while (!atomic_compare_exchange_weak_acquire (&rwlock->__data.__readers,
+ &r, rnew));
+
+ if ((r & PTHREAD_RWLOCK_WRPHASE) != 0)
+ {
+ //FIXME / TODO same as in rdlock_full
+ int private = __pthread_rwlock_get_private (rwlock);
+ atomic_store_release (&rwlock->__data.__wrphase_futex, 0);
+ futex_wake (&rwlock->__data.__wrphase_futex, INT_MAX, private);
+ }
- lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
+ return 0;
- if (wake)
- futex_wake (&rwlock->__data.__readers_wakeup, INT_MAX, futex_shared);
- return result;
}
strong_alias (__pthread_rwlock_tryrdlock, pthread_rwlock_tryrdlock)
@@ -18,31 +18,44 @@
#include <errno.h>
#include "pthreadP.h"
-#include <lowlevellock.h>
-#include <elide.h>
-
+#include <atomic.h>
+/* See pthread_rwlock_common.c for an overview. */
int
__pthread_rwlock_trywrlock (pthread_rwlock_t *rwlock)
{
- int result = EBUSY;
-
- if (ELIDE_TRYLOCK (rwlock->__data.__rwelision,
- rwlock->__data.__lock == 0
- && rwlock->__data.__nr_readers == 0
- && rwlock->__data.__writer, 1))
- return 0;
-
- lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
-
- if (rwlock->__data.__writer == 0 && rwlock->__data.__nr_readers == 0)
+ /* When in a trywrlock, we can acquire the write lock if it is in states
+ #1 (idle and read phase) and #5 (idle and write phase), and also in #6
+ (readers waiting, write phase) if we prefer writers.
+ If we observe any other state, we are allowed to fail and do not need to
+ "synchronize memory" as specified by POSIX (hence relaxed MO is
+ sufficient for the first load and the CAS failure path).
+ We face a similar issue as in tryrdlock in that we need to both avoid
+ live-locks / starvation and must not fail spuriously (see there for
+ further comments) -- and thus must loop until we get a definitive
+ observation or state change. */
+ unsigned int r = atomic_load_relaxed (&rwlock->__data.__readers);
+ bool prefer_writer =
+ (rwlock->__data.__flags != PTHREAD_RWLOCK_PREFER_READER_NP);
+ while (((r & PTHREAD_RWLOCK_WRLOCKED) == 0)
+ && (((r >> PTHREAD_RWLOCK_READER_SHIFT) == 0)
+ || (prefer_writer && ((r & PTHREAD_RWLOCK_WRPHASE) != 0))))
{
- rwlock->__data.__writer = THREAD_GETMEM (THREAD_SELF, tid);
- result = 0;
+ /* Try to transition to states #7 or #8 (i.e., acquire the lock). */
+ if (atomic_compare_exchange_weak_acquire (
+ &rwlock->__data.__readers, &r,
+ r | PTHREAD_RWLOCK_WRPHASE | PTHREAD_RWLOCK_WRLOCKED))
+ {
+ atomic_store_relaxed (&rwlock->__data.__writers_futex, 1);
+ atomic_store_relaxed (&rwlock->__data.__wrphase_futex, 1);
+ atomic_store_relaxed (&rwlock->__data.__cur_writer,
+ THREAD_GETMEM (THREAD_SELF, tid));
+ return 0;
+ }
+ /* TODO Back-off. */
+ /* See above. */
}
-
- lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
-
- return result;
+ return EBUSY;
}
+
strong_alias (__pthread_rwlock_trywrlock, pthread_rwlock_trywrlock)
@@ -18,56 +18,29 @@
#include <errno.h>
#include <sysdep.h>
-#include <lowlevellock.h>
#include <futex-internal.h>
#include <pthread.h>
#include <pthreadP.h>
#include <stap-probe.h>
-#include <elide.h>
+#include "pthread_rwlock_common.c"
-/* Unlock RWLOCK. */
+/* See pthread_rwlock_common.c for an overview. */
int
__pthread_rwlock_unlock (pthread_rwlock_t *rwlock)
{
- int futex_shared =
- rwlock->__data.__shared == LLL_PRIVATE ? FUTEX_PRIVATE : FUTEX_SHARED;
-
LIBC_PROBE (rwlock_unlock, 1, rwlock);
- if (ELIDE_UNLOCK (rwlock->__data.__writer == 0
- && rwlock->__data.__nr_readers == 0))
- return 0;
-
- lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
- if (rwlock->__data.__writer)
- rwlock->__data.__writer = 0;
+ /* We distinguish between having acquired a read vs. a write lock by looking
+ at the writer TID. If it's equal to our TID, we must be the writer
+ because nobody else can have stored this value. Also, if we are a
+ reader, we will read from the wrunlock store with value 0 by the most
+ recent writer because that writer happens-before us. */
+ if (atomic_load_relaxed (&rwlock->__data.__cur_writer)
+ == THREAD_GETMEM (THREAD_SELF, tid))
+ __pthread_rwlock_wrunlock (rwlock);
else
- --rwlock->__data.__nr_readers;
- /* If there are still readers present, we do not yet need to wake writers
- nor are responsible to wake any readers. */
- if (rwlock->__data.__nr_readers == 0)
- {
- /* Note that if there is a blocked writer, we effectively make it
- responsible for waking any readers because we don't wake readers in
- this case. */
- if (rwlock->__data.__nr_writers_queued)
- {
- ++rwlock->__data.__writer_wakeup;
- lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
- futex_wake (&rwlock->__data.__writer_wakeup, 1, futex_shared);
- return 0;
- }
- else if (rwlock->__data.__nr_readers_queued)
- {
- ++rwlock->__data.__readers_wakeup;
- lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
- futex_wake (&rwlock->__data.__readers_wakeup, INT_MAX,
- futex_shared);
- return 0;
- }
- }
- lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
+ __pthread_rwlock_rdunlock (rwlock);
return 0;
}
@@ -16,114 +16,18 @@
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
-#include <errno.h>
-#include <sysdep.h>
-#include <lowlevellock.h>
-#include <futex-internal.h>
-#include <pthread.h>
-#include <pthreadP.h>
-#include <stap-probe.h>
-#include <elide.h>
-
-
-/* Acquire write lock for RWLOCK. */
-static int __attribute__((noinline))
-__pthread_rwlock_wrlock_slow (pthread_rwlock_t *rwlock)
-{
- int result = 0;
- int futex_shared =
- rwlock->__data.__shared == LLL_PRIVATE ? FUTEX_PRIVATE : FUTEX_SHARED;
-
- /* Caller has taken the lock. */
-
- while (1)
- {
- /* Make sure we are not holding the rwlock as a writer. This is
- a deadlock situation we recognize and report. */
- if (__builtin_expect (rwlock->__data.__writer
- == THREAD_GETMEM (THREAD_SELF, tid), 0))
- {
- result = EDEADLK;
- break;
- }
-
- /* Remember that we are a writer. */
- if (++rwlock->__data.__nr_writers_queued == 0)
- {
- /* Overflow on number of queued writers. */
- --rwlock->__data.__nr_writers_queued;
- result = EAGAIN;
- break;
- }
-
- int waitval = rwlock->__data.__writer_wakeup;
-
- /* Free the lock. */
- lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
-
- /* Wait for the writer or reader(s) to finish. We do not check the
- return value because we decide how to continue based on the state of
- the rwlock. */
- futex_wait_simple (&rwlock->__data.__writer_wakeup, waitval,
- futex_shared);
-
- /* Get the lock. */
- lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
-
- /* To start over again, remove the thread from the writer list. */
- --rwlock->__data.__nr_writers_queued;
-
- /* Get the rwlock if there is no writer and no reader. */
- if (rwlock->__data.__writer == 0 && rwlock->__data.__nr_readers == 0)
- {
- /* Mark self as writer. */
- rwlock->__data.__writer = THREAD_GETMEM (THREAD_SELF, tid);
-
- LIBC_PROBE (wrlock_acquire_write, 1, rwlock);
- break;
- }
- }
-
- /* We are done, free the lock. */
- lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
-
- return result;
-}
-
-/* Fast path of acquiring write lock for RWLOCK. */
+#include "pthread_rwlock_common.c"
+/* See pthread_rwlock_common.c. */
int
__pthread_rwlock_wrlock (pthread_rwlock_t *rwlock)
{
LIBC_PROBE (wrlock_entry, 1, rwlock);
- if (ELIDE_LOCK (rwlock->__data.__rwelision,
- rwlock->__data.__lock == 0
- && rwlock->__data.__writer == 0
- && rwlock->__data.__nr_readers == 0))
- return 0;
-
- /* Make sure we are alone. */
- lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
-
- /* Get the rwlock if there is no writer and no reader. */
- if (__glibc_likely((rwlock->__data.__writer |
- rwlock->__data.__nr_readers) == 0))
- {
- /* Mark self as writer. */
- rwlock->__data.__writer = THREAD_GETMEM (THREAD_SELF, tid);
-
- LIBC_PROBE (wrlock_acquire_write, 1, rwlock);
-
- /* We are done, free the lock. */
- lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
-
- return 0;
- }
-
- return __pthread_rwlock_wrlock_slow (rwlock);
+ int result = __pthread_rwlock_wrlock_full (rwlock, NULL);
+ LIBC_PROBE (wrlock_acquire_write, 1, rwlock);
+ return result;
}
-
weak_alias (__pthread_rwlock_wrlock, pthread_rwlock_wrlock)
hidden_def (__pthread_rwlock_wrlock)
@@ -16,5 +16,5 @@
License along with the GNU C Library; see the file COPYING.LIB. If
not, see <http://www.gnu.org/licenses/>. */
-#define INIT PTHREAD_RWLOCK_INITIALIZER
+#define KIND PTHREAD_RWLOCK_PREFER_READER_NP
#include "tst-rwlock8.c"
@@ -16,5 +16,5 @@
License along with the GNU C Library; see the file COPYING.LIB. If
not, see <http://www.gnu.org/licenses/>. */
-#define INIT PTHREAD_RWLOCK_INITIALIZER
+#define KIND PTHREAD_RWLOCK_PREFER_READER_NP
#include "tst-rwlock9.c"
new file mode 100644
@@ -0,0 +1,19 @@
+/* Test program for timedout read/write lock functions.
+ Copyright (C) 2016 Free Software Foundation, Inc.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public License as
+ published by the Free Software Foundation; either version 2.1 of the
+ License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; see the file COPYING.LIB. If
+ not, see <http://www.gnu.org/licenses/>. */
+
+#define KIND PTHREAD_RWLOCK_PREFER_WRITER_NP
+#include "tst-rwlock8.c"
new file mode 100644
@@ -0,0 +1,19 @@
+/* Test program for timedout read/write lock functions.
+ Copyright (C) 2016 Free Software Foundation, Inc.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public License as
+ published by the Free Software Foundation; either version 2.1 of the
+ License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; see the file COPYING.LIB. If
+ not, see <http://www.gnu.org/licenses/>. */
+
+#define KIND PTHREAD_RWLOCK_PREFER_WRITER_NP
+#include "tst-rwlock9.c"
new file mode 100644
@@ -0,0 +1,127 @@
+/* Test rdlock overflow.
+ Copyright (C) 2000-2016 Free Software Foundation, Inc.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public License as
+ published by the Free Software Foundation; either version 2.1 of the
+ License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; see the file COPYING.LIB. If
+ not, see <http://www.gnu.org/licenses/>. */
+
+#include <errno.h>
+#include <error.h>
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
+#include <unistd.h>
+#include <pthreadP.h>
+
+
+#define NREADERS 15
+#define READTRIES 5000
+
+#define DELAY 1000000
+
+static pthread_rwlock_t lock = PTHREAD_RWLOCK_INITIALIZER;
+static int eagain_returned = 0;
+static int success_returned = 0;
+
+static void *
+reader_thread (void *nr)
+{
+ struct timespec delay;
+ int n;
+
+ delay.tv_sec = 0;
+ delay.tv_nsec = DELAY;
+
+ for (n = 0; n < READTRIES; ++n)
+ {
+ int err = pthread_rwlock_rdlock (&lock);
+ if (err == EAGAIN)
+ {
+ atomic_store_relaxed (&eagain_returned, 1);
+ continue;
+ }
+ else if (err == 0)
+ atomic_store_relaxed (&success_returned, 1);
+ else
+ {
+ puts ("rdlock failed");
+ exit (1);
+ }
+
+ nanosleep (&delay, NULL);
+
+ if (pthread_rwlock_unlock (&lock) != 0)
+ {
+ puts ("unlock for reader failed");
+ exit (1);
+ }
+ }
+
+ return NULL;
+}
+
+
+static int
+do_test (void)
+{
+ pthread_t thrd[NREADERS];
+ int n;
+ void *res;
+
+ /* Set the rwlock so that it's close to a reader overflow.
+ PTHREAD_RWLOCK_WRPHASE and PTHREAD_RWLOCK_WRLOCK are zero initially. */
+ unsigned int readers = PTHREAD_RWLOCK_READER_OVERFLOW
+ - ((NREADERS / 3) << PTHREAD_RWLOCK_READER_SHIFT);
+ lock.__data.__readers = readers;
+
+ for (n = 0; n < NREADERS; ++n)
+ if (pthread_create (&thrd[n], NULL, reader_thread,
+ (void *) (long int) n) != 0)
+ {
+ puts ("reader create failed");
+ exit (1);
+ }
+
+ /* Wait for all the threads. */
+ for (n = 0; n < NREADERS; ++n)
+ if (pthread_join (thrd[n], &res) != 0)
+ {
+ puts ("reader join failed");
+ exit (1);
+ }
+
+ if (atomic_load_relaxed (&eagain_returned) == 0)
+ {
+ puts ("EAGAIN has never been returned");
+ exit (1);
+ }
+
+ if (atomic_load_relaxed (&success_returned) == 0)
+ {
+ puts ("rdlock was never successfully acquired");
+ exit (1);
+ }
+
+ if (lock.__data.__readers != readers)
+ {
+ puts ("__readers in rwlock differs from initial value");
+ exit (1);
+ }
+
+ return 0;
+}
+
+#define TIMEOUT 30
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"
new file mode 100644
@@ -0,0 +1,2 @@
+#define TYPE PTHREAD_RWLOCK_PREFER_WRITER_NP
+#include "tst-rwlock2.c"
@@ -32,11 +32,11 @@
#define DELAY 1000000
-#ifndef INIT
-# define INIT PTHREAD_RWLOCK_WRITER_NONRECURSIVE_INITIALIZER_NP
+#ifndef KIND
+# define KIND PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP
#endif
-static pthread_rwlock_t lock = INIT;
+static pthread_rwlock_t lock;
static void *
@@ -118,6 +118,25 @@ do_test (void)
pthread_t thrd[NREADERS];
int n;
void *res;
+ pthread_rwlockattr_t a;
+
+ if (pthread_rwlockattr_init (&a) != 0)
+ {
+ puts ("rwlockattr_t failed");
+ exit (1);
+ }
+
+ if (pthread_rwlockattr_setkind_np (&a, KIND) != 0)
+ {
+ puts ("rwlockattr_setkind failed");
+ exit (1);
+ }
+
+ if (pthread_rwlock_init (&lock, &a) != 0)
+ {
+ puts ("rwlock_init failed");
+ exit (1);
+ }
/* Make standard error the same as standard output. */
dup2 (1, 2);
@@ -34,11 +34,11 @@
#define TIMEOUT 1000000
#define DELAY 1000000
-#ifndef INIT
-# define INIT PTHREAD_RWLOCK_WRITER_NONRECURSIVE_INITIALIZER_NP
+#ifndef KIND
+# define KIND PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP
#endif
-static pthread_rwlock_t lock = INIT;
+static pthread_rwlock_t lock;
static void *
@@ -156,6 +156,25 @@ do_test (void)
pthread_t thrd[NREADERS];
int n;
void *res;
+ pthread_rwlockattr_t a;
+
+ if (pthread_rwlockattr_init (&a) != 0)
+ {
+ puts ("rwlockattr_t failed");
+ exit (1);
+ }
+
+ if (pthread_rwlockattr_setkind_np (&a, KIND) != 0)
+ {
+ puts ("rwlockattr_setkind failed");
+ exit (1);
+ }
+
+ if (pthread_rwlock_init (&lock, &a) != 0)
+ {
+ puts ("rwlock_init failed");
+ exit (1);
+ }
/* Make standard error the same as standard output. */
dup2 (1, 2);
@@ -125,13 +125,13 @@ typedef union
{
struct
{
- int __lock;
- unsigned int __nr_readers;
- unsigned int __readers_wakeup;
- unsigned int __writer_wakeup;
- unsigned int __nr_readers_queued;
- unsigned int __nr_writers_queued;
- int __writer;
+ unsigned int __readers;
+ unsigned int __writers;
+ unsigned int __wrphase_futex;
+ unsigned int __writers_futex;
+ unsigned int __pad3;
+ unsigned int __pad4;
+ int __cur_writer;
int __shared;
unsigned long int __pad1;
unsigned long int __pad2;
@@ -128,12 +128,12 @@ typedef union
{
struct
{
- int __lock;
- unsigned int __nr_readers;
- unsigned int __readers_wakeup;
- unsigned int __writer_wakeup;
- unsigned int __nr_readers_queued;
- unsigned int __nr_writers_queued;
+ unsigned int __readers;
+ unsigned int __writers;
+ unsigned int __wrphase_futex;
+ unsigned int __writers_futex;
+ unsigned int __pad3;
+ unsigned int __pad4;
#if __BYTE_ORDER == __BIG_ENDIAN
unsigned char __pad1;
unsigned char __pad2;
@@ -149,7 +149,7 @@ typedef union
unsigned char __pad1;
unsigned char __pad2;
#endif
- int __writer;
+ int __cur_writer;
} __data;
char __size[__SIZEOF_PTHREAD_RWLOCK_T];
long int __align;
@@ -168,13 +168,13 @@ typedef union
next four words are all set to 1 by the Linuxthreads
PTHREAD_RWLOCK_INITIALIZER. We ignore them in NPTL. */
int __compat_padding[4] __attribute__ ((__aligned__(16)));
- int __lock;
- unsigned int __nr_readers;
- unsigned int __readers_wakeup;
- unsigned int __writer_wakeup;
- unsigned int __nr_readers_queued;
- unsigned int __nr_writers_queued;
- int __writer;
+ unsigned int __readers;
+ unsigned int __writers;
+ unsigned int __wrphase_futex;
+ unsigned int __writers_futex;
+ unsigned int __pad3;
+ unsigned int __pad4;
+ int __cur_writer;
/* An unused word, reserved for future use. It was added
to maintain the location of the flags from the Linuxthreads
layout of this structure. */
@@ -125,13 +125,13 @@ typedef union
{
struct
{
- int __lock;
- unsigned int __nr_readers;
- unsigned int __readers_wakeup;
- unsigned int __writer_wakeup;
- unsigned int __nr_readers_queued;
- unsigned int __nr_writers_queued;
- int __writer;
+ unsigned int __readers;
+ unsigned int __writers;
+ unsigned int __wrphase_futex;
+ unsigned int __writers_futex;
+ unsigned int __pad3;
+ unsigned int __pad4;
+ int __cur_writer;
int __shared;
unsigned long int __pad1;
unsigned long int __pad2;
@@ -128,19 +128,19 @@ typedef union
{
struct
{
- int __lock __attribute__ ((__aligned__ (4)));
- unsigned int __nr_readers;
- unsigned int __readers_wakeup;
- unsigned int __writer_wakeup;
- unsigned int __nr_readers_queued;
- unsigned int __nr_writers_queued;
+ unsigned int __readers __attribute__ ((__aligned__ (4)));
+ unsigned int __writers;
+ unsigned int __wrphase_futex;
+ unsigned int __writers_futex;
+ unsigned int __pad3;
+ unsigned int __pad4;
unsigned char __pad1;
unsigned char __pad2;
unsigned char __shared;
/* FLAGS must stay at this position in the structure to maintain
binary compatibility. */
unsigned char __flags;
- int __writer;
+ int __cur_writer;
} __data;
char __size[__SIZEOF_PTHREAD_RWLOCK_T];
long int __align;
@@ -123,12 +123,12 @@ typedef union
{
struct
{
- int __lock;
- unsigned int __nr_readers;
- unsigned int __readers_wakeup;
- unsigned int __writer_wakeup;
- unsigned int __nr_readers_queued;
- unsigned int __nr_writers_queued;
+ unsigned int __readers;
+ unsigned int __writers;
+ unsigned int __wrphase_futex;
+ unsigned int __writers_futex;
+ unsigned int __pad3;
+ unsigned int __pad4;
# if __BYTE_ORDER == __BIG_ENDIAN
unsigned char __pad1;
unsigned char __pad2;
@@ -144,7 +144,7 @@ typedef union
unsigned char __pad1;
unsigned char __pad2;
# endif
- int __writer;
+ int __cur_writer;
} __data;
char __size[__SIZEOF_PTHREAD_RWLOCK_T];
long int __align;
@@ -158,13 +158,13 @@ typedef union
# if _MIPS_SIM == _ABI64
struct
{
- int __lock;
- unsigned int __nr_readers;
- unsigned int __readers_wakeup;
- unsigned int __writer_wakeup;
- unsigned int __nr_readers_queued;
- unsigned int __nr_writers_queued;
- int __writer;
+ unsigned int __readers;
+ unsigned int __writers;
+ unsigned int __wrphase_futex;
+ unsigned int __writers_futex;
+ unsigned int __pad3;
+ unsigned int __pad4;
+ int __cur_writer;
int __shared;
unsigned long int __pad1;
unsigned long int __pad2;
@@ -175,12 +175,12 @@ typedef union
# else
struct
{
- int __lock;
- unsigned int __nr_readers;
- unsigned int __readers_wakeup;
- unsigned int __writer_wakeup;
- unsigned int __nr_readers_queued;
- unsigned int __nr_writers_queued;
+ unsigned int __readers;
+ unsigned int __writers;
+ unsigned int __wrphase_futex;
+ unsigned int __writers_futex;
+ unsigned int __pad3;
+ unsigned int __pad4;
#if __BYTE_ORDER == __BIG_ENDIAN
unsigned char __pad1;
unsigned char __pad2;
@@ -196,7 +196,7 @@ typedef union
unsigned char __pad1;
unsigned char __pad2;
#endif
- int __writer;
+ int __cur_writer;
} __data;
# endif
char __size[__SIZEOF_PTHREAD_RWLOCK_T];
@@ -128,12 +128,12 @@ typedef union
{
struct
{
- int __lock;
- unsigned int __nr_readers;
- unsigned int __readers_wakeup;
- unsigned int __writer_wakeup;
- unsigned int __nr_readers_queued;
- unsigned int __nr_writers_queued;
+ unsigned int __readers;
+ unsigned int __writers;
+ unsigned int __wrphase_futex;
+ unsigned int __writers_futex;
+ unsigned int __pad3;
+ unsigned int __pad4;
#if __BYTE_ORDER == __BIG_ENDIAN
unsigned char __pad1;
unsigned char __pad2;
@@ -149,7 +149,7 @@ typedef union
unsigned char __pad1;
unsigned char __pad2;
#endif
- int __writer;
+ int __cur_writer;
} __data;
char __size[__SIZEOF_PTHREAD_RWLOCK_T];
long int __align;
@@ -178,13 +178,13 @@ typedef union
# if __WORDSIZE == 64
struct
{
- int __lock;
- unsigned int __nr_readers;
- unsigned int __readers_wakeup;
- unsigned int __writer_wakeup;
- unsigned int __nr_readers_queued;
- unsigned int __nr_writers_queued;
- int __writer;
+ unsigned int __readers;
+ unsigned int __writers;
+ unsigned int __wrphase_futex;
+ unsigned int __writers_futex;
+ unsigned int __pad3;
+ unsigned int __pad4;
+ int __cur_writer;
int __shared;
unsigned long int __pad1;
unsigned long int __pad2;
@@ -195,19 +195,19 @@ typedef union
# else
struct
{
- int __lock;
- unsigned int __nr_readers;
- unsigned int __readers_wakeup;
- unsigned int __writer_wakeup;
- unsigned int __nr_readers_queued;
- unsigned int __nr_writers_queued;
+ unsigned int __readers;
+ unsigned int __writers;
+ unsigned int __wrphase_futex;
+ unsigned int __writers_futex;
+ unsigned int __pad3;
+ unsigned int __pad4;
unsigned char __pad1;
unsigned char __pad2;
unsigned char __shared;
/* FLAGS must stay at this position in the structure to maintain
binary compatibility. */
unsigned char __flags;
- int __writer;
+ int __cur_writer;
} __data;
# endif
char __size[__SIZEOF_PTHREAD_RWLOCK_T];
@@ -128,12 +128,12 @@ typedef union
{
struct
{
- int __lock;
- unsigned int __nr_readers;
- unsigned int __readers_wakeup;
- unsigned int __writer_wakeup;
- unsigned int __nr_readers_queued;
- unsigned int __nr_writers_queued;
+ unsigned int __readers;
+ unsigned int __writers;
+ unsigned int __wrphase_futex;
+ unsigned int __writers_futex;
+ unsigned int __pad3;
+ unsigned int __pad4;
#if __BYTE_ORDER == __BIG_ENDIAN
unsigned char __pad1;
unsigned char __pad2;
@@ -149,7 +149,7 @@ typedef union
unsigned char __pad1;
unsigned char __pad2;
#endif
- pthread_t __writer;
+ pthread_t __cur_writer;
} __data;
char __size[__SIZEOF_PTHREAD_RWLOCK_T];
long int __align;
@@ -158,13 +158,13 @@ typedef union
# if __WORDSIZE == 64
struct
{
- int __lock;
- unsigned int __nr_readers;
- unsigned int __readers_wakeup;
- unsigned int __writer_wakeup;
- unsigned int __nr_readers_queued;
- unsigned int __nr_writers_queued;
- int __writer;
+ unsigned int __readers;
+ unsigned int __writers;
+ unsigned int __wrphase_futex;
+ unsigned int __writers_futex;
+ unsigned int __pad3;
+ unsigned int __pad4;
+ int __cur_writer;
int __shared;
unsigned long int __pad1;
unsigned long int __pad2;
@@ -175,19 +175,19 @@ typedef union
# else
struct
{
- int __lock;
- unsigned int __nr_readers;
- unsigned int __readers_wakeup;
- unsigned int __writer_wakeup;
- unsigned int __nr_readers_queued;
- unsigned int __nr_writers_queued;
+ unsigned int __readers;
+ unsigned int __writers;
+ unsigned int __wrphase_futex;
+ unsigned int __writers_futex;
+ unsigned int __pad3;
+ unsigned int __pad4;
unsigned char __pad1;
unsigned char __pad2;
unsigned char __shared;
/* FLAGS must stay at this position in the structure to maintain
binary compatibility. */
unsigned char __flags;
- int __writer;
+ int __cur_writer;
} __data;
# endif
char __size[__SIZEOF_PTHREAD_RWLOCK_T];
@@ -158,13 +158,13 @@ typedef union
# if __WORDSIZE == 64
struct
{
- int __lock;
- unsigned int __nr_readers;
- unsigned int __readers_wakeup;
- unsigned int __writer_wakeup;
- unsigned int __nr_readers_queued;
- unsigned int __nr_writers_queued;
- int __writer;
+ unsigned int __readers;
+ unsigned int __writers;
+ unsigned int __wrphase_futex;
+ unsigned int __writers_futex;
+ unsigned int __pad3;
+ unsigned int __pad4;
+ int __cur_writer;
int __shared;
unsigned long int __pad1;
unsigned long int __pad2;
@@ -175,19 +175,19 @@ typedef union
# else
struct
{
- int __lock;
- unsigned int __nr_readers;
- unsigned int __readers_wakeup;
- unsigned int __writer_wakeup;
- unsigned int __nr_readers_queued;
- unsigned int __nr_writers_queued;
+ unsigned int __readers;
+ unsigned int __writers;
+ unsigned int __wrphase_futex;
+ unsigned int __writers_futex;
+ unsigned int __pad3;
+ unsigned int __pad4;
/* FLAGS must stay at this position in the structure to maintain
binary compatibility. */
unsigned char __flags;
unsigned char __shared;
unsigned char __pad1;
unsigned char __pad2;
- int __writer;
+ int __cur_writer;
} __data;
# endif
char __size[__SIZEOF_PTHREAD_RWLOCK_T];
@@ -124,13 +124,13 @@ typedef union
{
struct
{
- int __lock;
- unsigned int __nr_readers;
- unsigned int __readers_wakeup;
- unsigned int __writer_wakeup;
- unsigned int __nr_readers_queued;
- unsigned int __nr_writers_queued;
- int __writer;
+ unsigned int __readers;
+ unsigned int __writers;
+ unsigned int __wrphase_futex;
+ unsigned int __writers_futex;
+ unsigned int __pad3;
+ unsigned int __pad4;
+ int __cur_writer;
int __shared;
unsigned long int __pad1;
unsigned long int __pad2;
@@ -164,13 +164,13 @@ typedef union
# if __WORDSIZE == 64
struct
{
- int __lock;
- unsigned int __nr_readers;
- unsigned int __readers_wakeup;
- unsigned int __writer_wakeup;
- unsigned int __nr_readers_queued;
- unsigned int __nr_writers_queued;
- int __writer;
+ unsigned int __readers;
+ unsigned int __writers;
+ unsigned int __wrphase_futex;
+ unsigned int __writers_futex;
+ unsigned int __pad3;
+ unsigned int __pad4;
+ int __cur_writer;
int __shared;
unsigned char __rwelision;
unsigned char __pad1[7];
@@ -183,19 +183,19 @@ typedef union
# else
struct
{
- int __lock;
- unsigned int __nr_readers;
- unsigned int __readers_wakeup;
- unsigned int __writer_wakeup;
- unsigned int __nr_readers_queued;
- unsigned int __nr_writers_queued;
+ unsigned int __readers;
+ unsigned int __writers;
+ unsigned int __wrphase_futex;
+ unsigned int __writers_futex;
+ unsigned int __pad3;
+ unsigned int __pad4;
unsigned char __rwelision;
unsigned char __pad2;
unsigned char __shared;
/* FLAGS must stay at this position in the structure to maintain
binary compatibility. */
unsigned char __flags;
- int __writer;
+ int __cur_writer;
#define __PTHREAD_RWLOCK_ELISION_EXTRA 0
} __data;
# endif
@@ -176,13 +176,13 @@ typedef union
# ifdef __x86_64__
struct
{
- int __lock;
- unsigned int __nr_readers;
- unsigned int __readers_wakeup;
- unsigned int __writer_wakeup;
- unsigned int __nr_readers_queued;
- unsigned int __nr_writers_queued;
- int __writer;
+ unsigned int __readers;
+ unsigned int __writers;
+ unsigned int __wrphase_futex;
+ unsigned int __writers_futex;
+ unsigned int __pad3;
+ unsigned int __pad4;
+ int __cur_writer;
int __shared;
signed char __rwelision;
# ifdef __ILP32__
@@ -201,12 +201,12 @@ typedef union
# else
struct
{
- int __lock;
- unsigned int __nr_readers;
- unsigned int __readers_wakeup;
- unsigned int __writer_wakeup;
- unsigned int __nr_readers_queued;
- unsigned int __nr_writers_queued;
+ unsigned int __readers;
+ unsigned int __writers;
+ unsigned int __wrphase_futex;
+ unsigned int __writers_futex;
+ unsigned int __pad3;
+ unsigned int __pad4;
/* FLAGS must stay at this position in the structure to maintain
binary compatibility. */
unsigned char __flags;
@@ -214,7 +214,7 @@ typedef union
signed char __rwelision;
# define __PTHREAD_RWLOCK_ELISION_EXTRA 0
unsigned char __pad2;
- int __writer;
+ int __cur_writer;
} __data;
# endif
char __size[__SIZEOF_PTHREAD_RWLOCK_T];