Subj : Win32 condition variables & MySQL
To   : comp.programming.threads
From : d|dq
Date : Tue Aug 09 2005 07:52 pm

To my surprise, today, I realized MySQL uses the following technique:

/* Implementation of posix conditions */

typedef struct st_pthread_link {
   DWORD thread_id;
   struct st_pthread_link *next;
} pthread_link;

typedef struct {
   uint32 waiting;
#ifdef OS2
   HEV    semaphore;
#else
   HANDLE semaphore;
#endif
} pthread_cond_t;


#ifndef OS2
struct timespec {		/* For pthread_cond_timedwait() */
     time_t tv_sec;
     long tv_nsec;
};
#endif

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)
     return ENOMEM;
   return 0;
}

int pthread_cond_destroy(pthread_cond_t *cond)
{
	return CloseHandle(cond->semaphore) ? 0 : EINVAL;
}


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 ;
}

int pthread_cond_timedwait(pthread_cond_t *cond, pthread_mutex_t *mutex,
                            struct timespec *abstime)
{
   struct _timeb curtime;
   int result;
   long timeout;
   _ftime(&curtime);
   timeout= ((long) (abstime->tv_sec - curtime.time)*1000L +
		    (long)((abstime->tv_nsec/1000) - curtime.millitm)/1000L);
   if (timeout < 0)				/* Some safety */
     timeout = 0L;
   InterlockedIncrement(&cond->waiting);
   LeaveCriticalSection(mutex);
   result=WaitForSingleObject(cond->semaphore,timeout);
   InterlockedDecrement(&cond->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);
   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 ;
}

.