Bug#25042 OPTIMIZE TABLE cause race condition in IO CACHE SHARE

- The condition variable implementation "lost" a signal to
  WaitOnSingleObject when a semaphore was released.
- The signal could be consumed by a new call to pthread_cond_wait
  before all waiting threads had awoken.
- The new implementation of pthread_cond_* uses events
  instead of semaphores. It also uses an extra lock to protect entry
  into new cond wait before the broadcast has finished.

include/my_pthread.h

@@ -80,11 +80,17 @@ typedef struct st_pthread_link {
 
 typedef struct {
   uint32 waiting;
-#ifdef OS2
-  HEV    semaphore;
-#else
-  HANDLE semaphore;
-#endif
+  CRITICAL_SECTION lock_waiting;
+ 
+  enum {
+    SIGNAL= 0,
+    BROADCAST= 1,
+    MAX_EVENTS= 2
+  } EVENTS;
+
+  HANDLE events[MAX_EVENTS];
+  HANDLE broadcast_block_event;
+
 } pthread_cond_t;
 
 typedef int pthread_mutexattr_t;

mysys/my_wincond.c

@@ -27,27 +27,48 @@
 
 int pthread_cond_init(pthread_cond_t *cond, const pthread_condattr_t *attr)
 {
-  cond->waiting=0;
-  cond->semaphore=CreateSemaphore(NULL,0,0x7FFFFFFF,NullS);
-  if (!cond->semaphore)
+  cond->waiting= 0;
+  InitializeCriticalSection(&cond->lock_waiting);
+    
+  cond->events[SIGNAL]= CreateEvent(NULL,  /* no security */
+                                    FALSE, /* auto-reset event */
+                                    FALSE, /* non-signaled initially */
+                                    NULL); /* unnamed */
+
+  /* Create a manual-reset event. */
+  cond->events[BROADCAST]= CreateEvent(NULL,  /* no security */
+                                       TRUE,  /* manual-reset */
+                                       FALSE, /* non-signaled initially */
+                                       NULL); /* unnamed */
+
+
+  cond->broadcast_block_event= CreateEvent(NULL,  /* no security */
+                                           TRUE,  /* manual-reset */
+                                           TRUE,  /* signaled initially */
+                                           NULL); /* unnamed */
+  
+  if( cond->events[SIGNAL] == NULL ||
+      cond->events[BROADCAST] == NULL ||
+      cond->broadcast_block_event == NULL )
     return ENOMEM;
   return 0;
 }
 
 int pthread_cond_destroy(pthread_cond_t *cond)
 {
-  return CloseHandle(cond->semaphore) ? 0 : EINVAL;
+  DeleteCriticalSection(&cond->lock_waiting);
+
+  if (CloseHandle(cond->events[SIGNAL]) == 0 ||
+      CloseHandle(cond->events[BROADCAST]) == 0 ||
+      CloseHandle(cond->broadcast_block_event) == 0)
+    return EINVAL;
+  return 0;
 }
 
 
 int pthread_cond_wait(pthread_cond_t *cond, pthread_mutex_t *mutex)
 {
-  InterlockedIncrement(&cond->waiting);
-  LeaveCriticalSection(mutex);
-  WaitForSingleObject(cond->semaphore,INFINITE);
-  InterlockedDecrement(&cond->waiting);
-  EnterCriticalSection(mutex);
-  return 0 ;
+  return pthread_cond_timedwait(cond,mutex,NULL);
 }
 
 
@@ -57,52 +78,104 @@ int pthread_cond_timedwait(pthread_cond_t *cond, pthread_mutex_t *mutex,
   int result;
   long timeout; 
   union ft64 now;
-  
-  GetSystemTimeAsFileTime(&now.ft);
 
-  /*
-    Calculate time left to abstime
-    - subtract start time from current time(values are in 100ns units)
-    - convert to millisec by dividing with 10000
-  */
-  timeout= (long)((abstime->tv.i64 - now.i64) / 10000);
-  
-  /* Don't allow the timeout to be negative */
-  if (timeout < 0)
-    timeout= 0L;
+  if( abstime != NULL )
+  {
+    GetSystemTimeAsFileTime(&now.ft);
+
+    /*
+      Calculate time left to abstime
+      - subtract start time from current time(values are in 100ns units)
+      - convert to millisec by dividing with 10000
+    */
+    timeout= (long)((abstime->tv.i64 - now.i64) / 10000);
+    
+    /* Don't allow the timeout to be negative */
+    if (timeout < 0)
+      timeout= 0L;
+
+    /*
+      Make sure the calucated timeout does not exceed original timeout
+      value which could cause "wait for ever" if system time changes
+    */
+    if (timeout > abstime->max_timeout_msec)
+      timeout= abstime->max_timeout_msec;
 
-  /*
-    Make sure the calucated timeout does not exceed original timeout
-    value which could cause "wait for ever" if system time changes
+  }
+  else
+  {
+    /* No time specified; don't expire */
+    timeout= INFINITE;
+  }
+
+  /* 
+    Block access if previous broadcast hasn't finished.
+    This is just for safety and should normally not
+    affect the total time spent in this function.
   */
-  if (timeout > abstime->max_timeout_msec)
-    timeout= abstime->max_timeout_msec;
+  WaitForSingleObject(cond->broadcast_block_event, INFINITE);
+
+  EnterCriticalSection(&cond->lock_waiting);
+  cond->waiting++;
+  LeaveCriticalSection(&cond->lock_waiting);
 
-  InterlockedIncrement(&cond->waiting);
   LeaveCriticalSection(mutex);
-  result= WaitForSingleObject(cond->semaphore,timeout);
-  InterlockedDecrement(&cond->waiting);
+
+  result= WaitForMultipleObjects(2, cond->events, FALSE, timeout);
+  
+  EnterCriticalSection(&cond->lock_waiting);
+  cond->waiting--;
+  
+  if (cond->waiting == 0 && result == (WAIT_OBJECT_0+BROADCAST))
+  {
+    /*
+      We're the last waiter to be notified or to stop waiting, so
+      reset the manual event. 
+    */
+    /* Close broadcast gate */
+    ResetEvent(cond->events[BROADCAST]);
+    /* Open block gate */
+    SetEvent(cond->broadcast_block_event);
+  }
+  LeaveCriticalSection(&cond->lock_waiting);
+  
   EnterCriticalSection(mutex);
 
   return result == WAIT_TIMEOUT ? ETIMEDOUT : 0;
 }
 
-
 int pthread_cond_signal(pthread_cond_t *cond)
 {
-  long prev_count;
-  if (cond->waiting)
-    ReleaseSemaphore(cond->semaphore,1,&prev_count);
+  EnterCriticalSection(&cond->lock_waiting);
+  
+  if(cond->waiting > 0)
+    SetEvent(cond->events[SIGNAL]);
+
+  LeaveCriticalSection(&cond->lock_waiting);
+  
   return 0;
 }
 
 
 int pthread_cond_broadcast(pthread_cond_t *cond)
 {
-  long prev_count;
-  if (cond->waiting)
-    ReleaseSemaphore(cond->semaphore,cond->waiting,&prev_count);
-  return 0 ;
+  EnterCriticalSection(&cond->lock_waiting);
+  /*
+     The mutex protect us from broadcasting if
+     there isn't any thread waiting to open the
+     block gate after this call has closed it.
+   */
+  if(cond->waiting > 0)
+  {
+    /* Close block gate */
+    ResetEvent(cond->broadcast_block_event); 
+    /* Open broadcast gate */
+    SetEvent(cond->events[BROADCAST]);
+  }
+
+  LeaveCriticalSection(&cond->lock_waiting);  
+
+  return 0;
 }