MySQL Bugs: #30992: Wrong implementation of pthread_mutex

Bug #30992	Wrong implementation of pthread_mutex_trylock()
Submitted:	13 Sep 2007 7:55	Modified:	24 Oct 2007 19:31
Reporter:	Mats Kindahl	Email Updates:
Status:	Closed	Impact on me:	None
Category:	MySQL Server: C API (client library)	Severity:	S3 (Non-critical)
Version:	5.0	OS:	Any
Assigned to:	Magnus Blåudd	CPU Architecture:	Any

Description:
Pthread_mutex_trylock() should return immediately if it cannot acquire the lock. This is not the behaviour when using safe_mutex(), which attempts to lock the mutex in the same manner as pthread_mutex_lock().

Pthread_mutex_trylock() should also return EBUSY when the lock cannot be acquired, but this is not the case when compiling for windows, where it is defined to return either 0 or 1.

How to repeat:
Read the code

Suggested fix:
Fix the windows mapping to return the correct constant.

Fix the implementation of safe_mutex to be able to return immediately if the lock is already locked.

Thank you for the bug report.

A patch for this bug has been committed. After review, it may
be pushed to the relevant source trees for release in the next
version. You can access the patch from:

  http://lists.mysql.com/commits/34856

ChangeSet@1.2526, 2007-10-03 21:38:32+02:00, msvensson@pilot.mysql.com +2 -0
  Bug#30992 Wrong implementation of pthread_mutex_trylock()
  It's not possible to use WaitForSingleObject to wait
  on a CRITICAL_SECTION, instead use the TryEnterCriticalSection function.
   - if "mutex" was already taken => return EBUSY
   - if "mutex" was aquired => return 0

Pushed into 5.1.23-beta

Pushed into 5.0.52

Noted in 5.0.52, 5.1.23 changelogs.