mbox series

[00/10] C++20 atomic wait/notify ABI stabilization

Message ID 20250110212810.832494-1-jwakely@redhat.com
Headers
Series C++20 atomic wait/notify ABI stabilization |

Message

Jonathan Wakely Jan. 10, 2025, 9:23 p.m. UTC 
  From: Jonathan Wakely <redi@gcc.gnu.org>

This series complete Tom's work to refactor the C++20 atomic wait/notify
code. The goal is to make the implementation ready for some pieces to be
moved into libstdc++.so instead of defining everything inline in the
headers.

Also available for review at
https://forge.sourceware.org/gcc/gcc-TEST/pulls/31

This fixes:

- PR 99572 - std::counting_semaphore coalescing wakes
- PR 104928 - std::counting_semaphore on Linux can sleep forever
- PR 118395 - Constructor of std::barrier is not constexpr

Partially fixed:

- PR 98749 - No precondition checks in <semaphore>, <latch> and <barrier>

Not fixed:

- PR 115955 - atomic<T>::wait _S_for uses a poor hash function
- PR 110854 - constructor of std::counting_semaphore is not constexpr
- PR 118402 - std::barrier doesn't use futex directly

All tests pass on x86_64-linux (although I should add more tests for the
semaphore bugs in the first two PRs above). I see one remaining failure
on sparc-solaris due to a timeout:

FAIL: 30_threads/semaphore/try_acquire.cc  -std=gnu++20 execution test

I still need to analyze that.

Thomas Rodgers (2):
  libstdc++: Atomic wait/notify ABI stabilization
  libstdc++: Pass __wait_args to internal API by const pointer

Jonathan Wakely (8):
  libstdc++: Whitespace fixes in atomic wait/notify code
  libstdc++: Various fixes for atomic wait/notify code
  libstdc++: Fix race condition in new atomic notify code
  libstdc++: Simplify futex wrapper functions for atomic wait/notify
  libstdc++: Remove reinterpret_cast uses in atomic wait/notify
  libstdc++: Rename __atomic_compare to __atomic_eq
  libstdc++: Use safe integer comparisons in std::latch [PR98749]
  libstdc++: Optimise std::latch::arrive_and_wait

 libstdc++-v3/include/bits/atomic_timed_wait.h | 539 +++++++----------
 libstdc++-v3/include/bits/atomic_wait.h       | 552 +++++++++---------
 libstdc++-v3/include/bits/semaphore_base.h    |  53 +-
 libstdc++-v3/include/std/barrier              |   6 +-
 libstdc++-v3/include/std/latch                |  51 +-
 .../29_atomics/atomic/wait_notify/100334.cc   |   4 +-
 .../29_atomics/atomic_integral/wait_notify.cc |   4 +
 7 files changed, 583 insertions(+), 626 deletions(-)