''

1 files changed, 56 insertions, 120 deletions

diff --git a/pthread_once.c b/pthread_once.c
index b42036f..39ddcce 100644
--- a/pthread_once.c
+++ b/pthread_once.c
@@ -34,77 +34,6 @@
  *      59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  */
 
-/*
- * NOTES:
- * pthread_once() performs a very simple task. So why is this implementation
- * so complicated?
- *
- * The original implementation WAS very simple, but it relied on Windows random
- * priority boosting to resolve starvation problems. Windows priority boosting
- * does not occur for realtime priority classes (levels 16 to 31).
- *
- * You can check back to previous versions of code in the CVS repository or
- * search the mailing list archives for discussion.
- *
- * Version A
- * ---------
- * Waiting threads would resume and suspend again using Sleep(0) until the
- * init_routine had completed, but a higher priority waiter could hog the CPU and
- * starve the initter thread until Windows randomly boosted it's priority, or forever
- * for realtime applications.
- *
- * Version B
- * ---------
- * This was fixed by introducing a per once_control manual-reset event that is
- * created and destroyed dynamically only if there are waiters. The design did not
- * need global critical sections. Each once_control remained independent. A waiter
- * could be confident that if the event was not null then it did not need to create
- * the event.
- *
- * Version C
- * ---------
- * Since a change in ABI would result from version B, it was decided to take
- * the opportunity and make pthread_once() fully compliant with the Single Unix
- * Specification (version 3 at the time). This required allowing the init_routine
- * to be a cancelation point. A cancelation meant that at least some waiting threads
- * if any had to be woken so that one might become the new initter thread.
- * Waiters could no longer simply assume that, if the event was not null, it did
- * not need to create an event.
- *
- * Also, the cancelled init thread needed to set the event, and the
- * new init thread (the winner of the race between any newly arriving threads and
- * waking waiters) would need to reset it again. In the meantime, threads could be
- * happily looping around until they either suspended on the reset event, or exited
- * because the init thread had completed. It was also once again possible for a higher
- * priority waiter to starve the init thread.
- * 
- * Version D
- * ---------
- * There were now two options considered:
- * - use an auto-reset event; OR
- * - add our own priority boosting.
- *
- * An auto-reset event would stop threads from looping ok, but it makes threads
- * dependent on earlier threads to successfully set the event in turn when it's time
- * to wake up, and this serialises threads unecessarily on MP systems. It also adds
- * an extra kernel call for each waking thread. If one waiter wakes and dies (async
- * cancelled or killed) before it can set the event, then all remaining waiters are
- * stranded.
- *
- * Priority boosting is a standard method for solving priority inversion and
- * starvation problems. Furthermore, all of the priority boost logic can
- * be restricted to the post cancellation tracks. That is, it need not slow
- * the normal cancel-free behaviour. Threads remain independent of other threads.
- *
- * Version E
- * ---------
- * Substituting a semaphore in place of the event achieves the same effect as an
- * auto-reset event in the post cancellation phase, and a manual-reset event in the
- * normal exit phase. The new initter thread does not need to do any post-cancellation
- * operations, and waiters only need to check that there is a new initter running
- * before starting to wait. All priority issues and adjustments disappear.
- */
-
 #include "pthread.h"
 #include "implement.h"
 
@@ -114,7 +43,7 @@ ptw32_once_init_routine_cleanup(void * arg)
 {
   pthread_once_t * once_control = (pthread_once_t *) arg;
 
-  (void) PTW32_INTERLOCKED_EXCHANGE((LPLONG)&once_control->started, (LONG)PTW32_FALSE);
+  (void) PTW32_INTERLOCKED_EXCHANGE((LPLONG)&once_control->state, (LONG)PTW32_ONCE_INIT);
 
   if (InterlockedExchangeAdd((LPLONG)&once_control->semaphore, 0L)) /* MBR fence */
     {
@@ -162,6 +91,7 @@ pthread_once (pthread_once_t * once_control, void (*init_routine) (void))
       */
 {
   int result;
+  int state;
   HANDLE sema;
 
   if (once_control == NULL || init_routine == NULL)
@@ -174,69 +104,75 @@ pthread_once (pthread_once_t * once_control, void (*init_routine) (void))
       result = 0;
     }
 
-  while (!InterlockedExchangeAdd((LPLONG)&once_control->done, 0L)) /* Atomic Read */
+  while ((state =
+	  PTW32_INTERLOCKED_COMPARE_EXCHANGE((PTW32_INTERLOCKED_LPLONG)&once_control->state,
+					     (PTW32_INTERLOCKED_LONG)PTW32_ONCE_STARTED,
+					     (PTW32_INTERLOCKED_LONG)PTW32_ONCE_INIT))
+	 != PTW32_ONCE_DONE)
     {
-      if (!PTW32_INTERLOCKED_EXCHANGE((LPLONG)&once_control->started, (LONG)PTW32_TRUE))
-	{
+      if (PTW32_ONCE_INIT == state)
+        {
 
 #ifdef _MSC_VER
 #pragma inline_depth(0)
 #endif
 
-	  pthread_cleanup_push(ptw32_once_init_routine_cleanup, (void *) once_control);
-	  (*init_routine)();
-	  pthread_cleanup_pop(0);
+          pthread_cleanup_push(ptw32_once_init_routine_cleanup, (void *) once_control);
+          (*init_routine)();
+          pthread_cleanup_pop(0);
 
 #ifdef _MSC_VER
 #pragma inline_depth()
 #endif
 
-	  (void) PTW32_INTERLOCKED_EXCHANGE((LPLONG)&once_control->done, (LONG)PTW32_TRUE);
-
-	  /*
-	   * we didn't create the semaphore.
-	   * it is only there if there is someone waiting.
-	   */
-	  if (InterlockedExchangeAdd((LPLONG)&once_control->semaphore, 0L)) /* MBR fence */
-	    {
-	      ReleaseSemaphore(once_control->semaphore, once_control->numSemaphoreUsers, NULL);
-	    }
-	}
+          (void) PTW32_INTERLOCKED_EXCHANGE((LPLONG)&once_control->state, 
+                                            (LONG)PTW32_ONCE_DONE);
+
+          /*
+           * we didn't create the semaphore.
+           * it is only there if there is someone waiting.
+           */
+          if (InterlockedExchangeAdd((LPLONG)&once_control->semaphore, 0L)) /* MBR fence */
+            {
+              ReleaseSemaphore(once_control->semaphore, 
+                               once_control->numSemaphoreUsers, NULL);
+            }
+        }
       else
-	{
-	  InterlockedIncrement((LPLONG)&once_control->numSemaphoreUsers);
+        {
+          InterlockedIncrement((LPLONG)&once_control->numSemaphoreUsers);
 
-	  if (!InterlockedExchangeAdd((LPLONG)&once_control->semaphore, 0L)) /* MBR fence */
-	    {
-	      sema = CreateSemaphore(NULL, 0, INT_MAX, NULL);
+          if (!InterlockedExchangeAdd((LPLONG)&once_control->semaphore, 0L)) /* MBR fence */
+            {
+              sema = CreateSemaphore(NULL, 0, INT_MAX, NULL);
 
-	      if (PTW32_INTERLOCKED_COMPARE_EXCHANGE((PTW32_INTERLOCKED_LPLONG)&once_control->semaphore,
+              if (PTW32_INTERLOCKED_COMPARE_EXCHANGE((PTW32_INTERLOCKED_LPLONG)&once_control->semaphore,
 						     (PTW32_INTERLOCKED_LONG)sema,
 						     (PTW32_INTERLOCKED_LONG)0))
-		{
-		  CloseHandle(sema);
-		}
-	    }
-
-	  /*
-	   * Check 'done' and 'started' again in case the initting thread has finished or cancelled
-	   * and left before seeing that there was a semaphore to release.
-	   */
-	  if (InterlockedExchangeAdd((LPLONG)&once_control->done, 0L) /* Done immediately, or */
-	      || !InterlockedExchangeAdd((LPLONG)&once_control->started, 0L) /* No initter yet, or */
-	      || WaitForSingleObject(once_control->semaphore, INFINITE)) /* Done or Cancelled */
-	    {
-	      if (0 == InterlockedDecrement((LPLONG)&once_control->numSemaphoreUsers))
-		{
-		  /* we were last */
-		  if ((sema = (HANDLE) PTW32_INTERLOCKED_EXCHANGE((LPLONG)&once_control->semaphore,
-								  (LONG)0)))
-		    {
-		      CloseHandle(sema);
-		    }
-		}
-	    }
-	}
+                {
+                  CloseHandle(sema);
+                }
+            }
+
+          /*
+           * Check 'state' again in case the initting thread has finished or
+	   * cancelled and left before seeing that there was a semaphore.
+           */
+          if (InterlockedExchangeAdd((LPLONG)&once_control->state, 0L) == PTW32_ONCE_STARTED)
+            {
+              WaitForSingleObject(once_control->semaphore, INFINITE);
+            }
+
+          if (0 == InterlockedDecrement((LPLONG)&once_control->numSemaphoreUsers))
+            {
+              /* we were last */
+              if ((sema =
+		   (HANDLE) PTW32_INTERLOCKED_EXCHANGE((LPLONG)&once_control->semaphore, (LONG)0)))
+                {
+                  CloseHandle(sema);
+                }
+            }
+        }
     }
 
   /*
@@ -246,4 +182,4 @@ pthread_once (pthread_once_t * once_control, void (*init_routine) (void))
    */
 FAIL0:
   return (result);
-}                                               /* pthread_once */ 
+}                               /* pthread_once */