diff mbox

[PING,v2] Fix mutex pretty printer test and pretty printer output

Message ID 1484917064-5206-1-git-send-email-omgalvan.86@gmail.com
State New, archived
Headers show

Commit Message

Martin Galvan Jan. 20, 2017, 12:57 p.m. UTC
This is a new version of the patch Torvald posted here:

https://www.sourceware.org/ml/libc-alpha/2017-01/msg00169.html

This fixes the mutex pretty printer so that, if the owner ID isn't recorded
(such as in the current lock elision implementation), "Owner ID" will be shown
as "Unknown" instead of 0. It also changes the mutex printer output so that it says
"Acquired" instead of "Locked". The mutex tests are updated accordingly.

In addition, I've added a paragraph to the "Known issues" section of the printers
README explaining that the printer output isn't guaranteed to cover every detail,
as we discussed with Torvald in that same thread.

I don't have write access, so somebody should commit this for me. Thanks.

ChangeLog:

2017-01-14  Martin Galvan  <martingalvan@sourceware.org>

	* README.pretty-printers (Known issues): Warn about printers not always
	covering everything.
	* nptl/nptl-printers.py (MutexPrinter): Change output.
	* nptl/test-mutex-printers.py: Fix test and adapt to changed output.

---
 README.pretty-printers      |  7 ++++++-
 nptl/nptl-printers.py       | 33 ++++++++++++++++++++-------------
 nptl/test-mutex-printers.py | 17 ++++++++++-------
 3 files changed, 36 insertions(+), 21 deletions(-)

--
2.7.4

Comments

Torvald Riegel Jan. 20, 2017, 2:28 p.m. UTC | #1
On Fri, 2017-01-20 at 09:57 -0300, Martin Galvan wrote:
> This is a new version of the patch Torvald posted here:
> 
> https://www.sourceware.org/ml/libc-alpha/2017-01/msg00169.html
> 
> This fixes the mutex pretty printer so that, if the owner ID isn't recorded
> (such as in the current lock elision implementation), "Owner ID" will be shown
> as "Unknown" instead of 0. It also changes the mutex printer output so that it says
> "Acquired" instead of "Locked". The mutex tests are updated accordingly.
> 
> In addition, I've added a paragraph to the "Known issues" section of the printers
> README explaining that the printer output isn't guaranteed to cover every detail,
> as we discussed with Torvald in that same thread.
> 
> I don't have write access, so somebody should commit this for me. Thanks.

Thanks.  Committed.
diff mbox

Patch

diff --git a/README.pretty-printers b/README.pretty-printers
index a2536ca..2522cb8 100644
--- a/README.pretty-printers
+++ b/README.pretty-printers
@@ -29,7 +29,7 @@  However, with a pretty printer gdb will output something like this:
 (gdb) print mutex
 $1 = pthread_mutex_t = {
   Type = Normal,
-  Status = Unlocked,
+  Status = Not acquired,
   Robust = No,
   Shared = No,
   Protocol = Priority protect,
@@ -145,6 +145,11 @@  any changes to the target code must also update the corresponding printers.
 On the plus side, the printer code itself may serve as a kind of documentation
 for the target code.

+* There's no guarantee that the information the pretty printers provide is
+complete, i.e. some details might be left off.  For example, the pthread_mutex_t
+printers won't report whether a thread is spin-waiting in an attempt to acquire
+the mutex.
+
 * Older versions of the gdb Python API have a bug where
 gdb.RegexpCollectionPrettyPrinter would not be able to get a value's real type
 if it was typedef'd.  This would cause gdb to ignore the pretty printers for
diff --git a/nptl/nptl-printers.py b/nptl/nptl-printers.py
index 9d67865..572a25c 100644
--- a/nptl/nptl-printers.py
+++ b/nptl/nptl-printers.py
@@ -101,9 +101,9 @@  class MutexPrinter(object):
     def read_status(self):
         """Read the mutex's status.

-        For architectures which support lock elision, this method reads
-        whether the mutex appears as locked in memory (i.e. it may show it as
-        unlocked even after calling pthread_mutex_lock).
+        Architectures that support lock elision might not record the mutex owner
+        ID in the __owner field.  In that case, the owner will be reported as
+        "Unknown".
         """

         if self.kind == PTHREAD_MUTEX_DESTROYED:
@@ -124,13 +124,14 @@  class MutexPrinter(object):
         """

         if self.lock == PTHREAD_MUTEX_UNLOCKED:
-            self.values.append(('Status', 'Unlocked'))
+            self.values.append(('Status', 'Not acquired'))
         else:
             if self.lock & FUTEX_WAITERS:
-                self.values.append(('Status', 'Locked, possibly with waiters'))
+                self.values.append(('Status',
+                                    'Acquired, possibly with waiters'))
             else:
                 self.values.append(('Status',
-                                    'Locked, possibly with no waiters'))
+                                    'Acquired, possibly with no waiters'))

             if self.lock & FUTEX_OWNER_DIED:
                 self.values.append(('Owner ID', '%d (dead)' % self.owner))
@@ -147,7 +148,7 @@  class MutexPrinter(object):
     def read_status_no_robust(self):
         """Read the status of a non-robust mutex.

-        Read info on whether the mutex is locked, if it may have waiters
+        Read info on whether the mutex is acquired, if it may have waiters
         and its owner (if any).
         """

@@ -157,7 +158,7 @@  class MutexPrinter(object):
             lock_value &= ~(PTHREAD_MUTEX_PRIO_CEILING_MASK)

         if lock_value == PTHREAD_MUTEX_UNLOCKED:
-            self.values.append(('Status', 'Unlocked'))
+            self.values.append(('Status', 'Not acquired'))
         else:
             if self.kind & PTHREAD_MUTEX_PRIO_INHERIT_NP:
                 waiters = self.lock & FUTEX_WAITERS
@@ -168,12 +169,18 @@  class MutexPrinter(object):
                 owner = self.owner

             if waiters:
-                self.values.append(('Status', 'Locked, possibly with waiters'))
+                self.values.append(('Status',
+                                    'Acquired, possibly with waiters'))
             else:
                 self.values.append(('Status',
-                                    'Locked, possibly with no waiters'))
+                                    'Acquired, possibly with no waiters'))

-            self.values.append(('Owner ID', owner))
+            if self.owner != 0:
+                self.values.append(('Owner ID', owner))
+            else:
+                # Owner isn't recorded, probably because lock elision
+                # is enabled.
+                self.values.append(('Owner ID', 'Unknown'))

     def read_attributes(self):
         """Read the mutex's attributes."""
@@ -208,14 +215,14 @@  class MutexPrinter(object):
     def read_misc_info(self):
         """Read miscellaneous info on the mutex.

-        For now this reads the number of times a recursive mutex was locked
+        For now this reads the number of times a recursive mutex was acquired
         by the same thread.
         """

         mutex_type = self.kind & PTHREAD_MUTEX_KIND_MASK

         if mutex_type == PTHREAD_MUTEX_RECURSIVE and self.count > 1:
-            self.values.append(('Times locked recursively', self.count))
+            self.values.append(('Times acquired by the owner', self.count))

 class MutexAttributesPrinter(object):
     """Pretty printer for pthread_mutexattr_t.
diff --git a/nptl/test-mutex-printers.py b/nptl/test-mutex-printers.py
index 23f16b0..687a32c 100644
--- a/nptl/test-mutex-printers.py
+++ b/nptl/test-mutex-printers.py
@@ -39,15 +39,18 @@  try:

     break_at(test_source, 'Test status (non-robust)')
     continue_cmd() # Go to test_status_no_robust
-    test_printer(var, to_string, {'Status': 'Unlocked'})
+    test_printer(var, to_string, {'Status': 'Not acquired'})
     next_cmd()
     thread_id = get_current_thread_lwpid()
-    test_printer(var, to_string, {'Status': 'Locked, possibly with no waiters',
-                                  'Owner ID': thread_id})
+    # Owner ID might be reported either as the thread ID or as "Unknown"
+    # (if e.g. lock elision is enabled).
+    test_printer(var, to_string,
+                 {'Status': 'Acquired, possibly with no waiters',
+                  'Owner ID': r'({0}|Unknown)'.format(thread_id)})

     break_at(test_source, 'Test status (robust)')
     continue_cmd() # Go to test_status_robust
-    test_printer(var, to_string, {'Status': 'Unlocked'})
+    test_printer(var, to_string, {'Status': 'Not acquired'})

     # We'll now test the robust mutex locking states.  We'll create a new
     # thread that will lock a robust mutex and exit without unlocking it.
@@ -75,15 +78,15 @@  try:
     test_printer(var, to_string, {'Owner ID': thread_id,
                            'State protected by this mutex': 'Inconsistent'})
     next_cmd()
-    test_printer(var, to_string, {'Status': 'Unlocked',
+    test_printer(var, to_string, {'Status': 'Not acquired',
                         'State protected by this mutex': 'Not recoverable'})
     set_scheduler_locking(False)

     break_at(test_source, 'Test recursive locks')
     continue_cmd() # Go to test_recursive_locks
-    test_printer(var, to_string, {'Times locked recursively': '2'})
+    test_printer(var, to_string, {'Times acquired by the owner': '2'})
     next_cmd()
-    test_printer(var, to_string, {'Times locked recursively': '3'})
+    test_printer(var, to_string, {'Times acquired by the owner': '3'})
     continue_cmd() # Exit

 except (NoLineError, pexpect.TIMEOUT) as exception: