BUG#30992 (Wrong implementation of pthread_mutex_trylock()):

Adding support for correct handling of pthread_mutex_trylock() on Win32
systems as well as when using the safe mutexes. 


include/my_pthread.h:
  Adding win_pthread_mutex_trylock() function as wrapper function for
  Windows implementation of pthread_mutex_trylock().
  
  Adding flag to safe_mutex_lock() that is shall not abort if the mutex
  is already locked and instead return EBUSY since this is the POSIX
  behaviour.
mysys/my_winthread.c:
  Added Win32 wrappper function to handle pthread_mutex_trylock().
mysys/thr_mutex.c:
  Added parameter 'try_lock' to safe_mutex_lock() to allow it to do double-
  duty as a pthread_mutex_trylock() in addition to working as
  pthread_mutex_lock().
  
  The code needs to return EBUSY instead of throwing an error in the event
  that the mutex is re-locked (we do not have recursive mutexes), but it
  also requires some special handling to avoid race conditions when
  calling the real pthread_mutex_{lock,trylock}().

1 files changed, 25 insertions, 0 deletions

diff --git a/mysys/my_winthread.c b/mysys/my_winthread.c
index 27ccaef4f23..e9fface0521 100644
--- a/mysys/my_winthread.c
+++ b/mysys/my_winthread.c
@@ -40,6 +40,31 @@ void win_pthread_init(void)
   pthread_mutex_init(&THR_LOCK_thread,MY_MUTEX_INIT_FAST);
 }
 
+/**
+   Adapter to @c pthread_mutex_trylock()
+
+   @retval 0      Mutex was acquired
+   @retval EBUSY  Mutex was already locked by a thread
+   @retval EINVAL Mutex could not be acquired due to other error
+ */
+int
+win_pthread_mutex_trylock(pthread_mutex_t *mutex)
+{
+  switch (WaitForSingleObject(mutex, 0)) {
+  case WAIT_TIMEOUT:
+    return EBUSY;
+
+  default:
+  case WAIT_FAILURE:
+    return EINVAL;
+
+  case WAIT_OBJECT_0:
+  case WAIT_ABANDONED: /* The mutex was acquired because it was
+                        * abandoned */
+    return 0;
+  }
+}
+
 /*
 ** We have tried to use '_beginthreadex' instead of '_beginthread' here
 ** but in this case the program leaks about 512 characters for each