On Fri, Jan 8, 2010 at 4:32 AM, Dmitry Potapov <dpotapov@xxxxxxxxx> wrote:
> On Thu, Jan 07, 2010 at 10:54:57PM +0100, Johannes Sixt wrote:
>> +
>> +int pthread_cond_wait(pthread_cond_t *cond, CRITICAL_SECTION *mutex)
>> +{
>> + /* serialize access to waiters count */
>> + EnterCriticalSection(&cond->waiters_lock);
>> + ++cond->waiters;
>> + LeaveCriticalSection(&cond->waiters_lock);
>
> InterlockedIncrement(&cond->waiters);
>
>> +
>> + /*
>> + * Unlock external mutex and wait for signal.
>> + * NOTE: we've held mutex locked long enough to increment
>> + * waiters count above, so there's no problem with
>> + * leaving mutex unlocked before we wait on semaphore.
>> + */
>> + LeaveCriticalSection(mutex);
>> +
>> + /* let's wait - ignore return value */
>> + WaitForSingleObject(cond->sema, INFINITE);
>> +
>> + /* we're done waiting, so make sure we decrease waiters count */
>> + EnterCriticalSection(&cond->waiters_lock);
>> + --cond->waiters;
>> + LeaveCriticalSection(&cond->waiters_lock);
>
> InterlockedDecrement(&cond->waiters);
Nice.
>> +
>> + /* lock external mutex again */
>> + EnterCriticalSection(mutex);
>> +
>> + return 0;
>> +}
>> +
>> +int pthread_cond_signal(pthread_cond_t *cond)
>> +{
>> + int have_waiters;
>> +
>> + /* serialize access to waiters count */
>> + EnterCriticalSection(&cond->waiters_lock);
>> + have_waiters = cond->waiters > 0;
>> + LeaveCriticalSection(&cond->waiters_lock);
>
> AFAIK, Win32 API assumes that reading LONG is always atomic, so
> the critical section is not really necesary here, but you need
> to declare 'waiters' as 'volatile':
"Simple reads and writes to properly-aligned 32-bit variables are
atomic operations."
http://msdn.microsoft.com/en-us/library/ms684122(VS.85).aspx
In other words: Yes, you are right.
>> +
>> +int pthread_cond_init(pthread_cond_t *cond, const void *unused)
>> +{
>> + cond->waiters = 0;
>> +
>> + InitializeCriticalSection(&cond->waiters_lock);
>
> Is waiters_lock really necessary?
(Yeah, I moved this one to the end)
No, I think you've proven that it isn't.
--
Erik "kusma" Faye-Lund
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