''

3 files changed, 26 insertions, 12 deletions

diff --git a/ChangeLog b/ChangeLog
index 3ba012b..d812aa5 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2005-04-27  Ross Johnson  <ross at callisto.canberra.edu.au>
+
+	* sem_wait.c (ptw32_sem_wait_cleanup): after cancellation re-attempt
+	to acquire the semaphore to avoid a race with a late sem_post.
+	* sem_timedwait.c: Modify comments.
+
 2005-04-25  Ross Johnson  <ross at callisto.canberra.edu.au>
 
 	* ptw32_relmillisecs.c: New module; converts future abstime to 
@@ -7,7 +13,7 @@
 	implemented for builds that define NEED_SEM (WinCE etc)
 	* sem_timedwait.c: Likewise; after timeout or cancellation,
 	re-attempt to acquire the semaphore in case one has been posted since
-	the timeout/cancel occurred. Thanks to 
+	the timeout/cancel occurred. Thanks to Stephan Mueller.
 	* Makefile: Add ptw32_relmillisecs.c module; remove
 	ptw32_{in,de}crease_semaphore.c modules.
 	* GNUmakefile: Likewise.
diff --git a/sem_timedwait.c b/sem_timedwait.c
index 186c123..deefa6e 100644
--- a/sem_timedwait.c
+++ b/sem_timedwait.c
@@ -62,7 +62,7 @@ ptw32_sem_timedwait_cleanup (void * args)
     {
       /*
        * We either timed out or were cancelled.
-       * If someone posted since then we try to take the semaphore.
+       * If someone has posted between then and now we try to take the semaphore.
        * Otherwise the semaphore count may be wrong after we
        * return. In the case of a cancellation, it is as if we
        * were cancelled just before we return (after taking the semaphore)
diff --git a/sem_wait.c b/sem_wait.c
index bcb17e8..05d7326 100644
--- a/sem_wait.c
+++ b/sem_wait.c
@@ -53,19 +53,27 @@ ptw32_sem_wait_cleanup(void * sem)
 
   if (pthread_mutex_lock (&s->lock) == 0)
     {
-      ++s->value;
-#ifdef NEED_SEM
-          
-      if (s->value > 0)
-	{
-	  s->leftToUnblock = 0;
-	}   
-#else 
       /*
-       * Don't release the W32 sema, it doesn't need adjustment
-       * because it doesn't record the number of waiters.
+       * If the sema is posted between us being cancelled and us locking
+       * the sema again above then we need to consume that post but cancel
+       * anyway. If we don't get the semaphore we indicate that we're no
+       * longer waiting.
        */
+      if (!(WaitForSingleObject(s->sem, 0) == WAIT_OBJECT_0))
+	{
+	  ++s->value;
+#ifdef NEED_SEM
+	  if (s->value > 0)
+	    {
+	      s->leftToUnblock = 0;
+	    }
+#else
+	  /*
+	   * Don't release the W32 sema, it doesn't need adjustment
+	   * because it doesn't record the number of waiters.
+	   */
 #endif /* NEED_SEM */
+	}
       (void) pthread_mutex_unlock (&s->lock);
     }
 }