wxMutexError wxMutex::Lock()
{
wxCHECK_MSG( m_internal, wxMUTEX_INVALID,
- _T("wxMutex::Lock(): not initialized") );
+ wxT("wxMutex::Lock(): not initialized") );
return m_internal->Lock();
}
wxMutexError wxMutex::LockTimeout(unsigned long ms)
{
wxCHECK_MSG( m_internal, wxMUTEX_INVALID,
- _T("wxMutex::Lock(): not initialized") );
+ wxT("wxMutex::Lock(): not initialized") );
return m_internal->Lock(ms);
}
wxMutexError wxMutex::TryLock()
{
wxCHECK_MSG( m_internal, wxMUTEX_INVALID,
- _T("wxMutex::TryLock(): not initialized") );
+ wxT("wxMutex::TryLock(): not initialized") );
return m_internal->TryLock();
}
wxMutexError wxMutex::Unlock()
{
wxCHECK_MSG( m_internal, wxMUTEX_INVALID,
- _T("wxMutex::Unlock(): not initialized") );
+ wxT("wxMutex::Unlock(): not initialized") );
return m_internal->Unlock();
}
wxMutex& m_mutex;
wxSemaphore m_semaphore;
- DECLARE_NO_COPY_CLASS(wxConditionInternal)
+ wxDECLARE_NO_COPY_CLASS(wxConditionInternal);
};
wxConditionInternal::wxConditionInternal(wxMutex& mutex)
m_mutex.Unlock();
- // a potential race condition can occur here
- //
- // after a thread increments m_numWaiters, and unlocks the mutex and before
- // the semaphore.Wait() is called, if another thread can cause a signal to
- // be generated
- //
- // this race condition is handled by using a semaphore and incrementing the
- // semaphore only if m_numWaiters is greater that zero since the semaphore,
- // can 'remember' signals the race condition will not occur
-
- // wait ( if necessary ) and decrement semaphore
- wxSemaError err = m_semaphore.Wait();
+ // after unlocking the mutex other threads may Signal() us, but it is ok
+ // now as we had already incremented m_numWaiters so Signal() will post the
+ // semaphore and decrement m_numWaiters back even if it is called before we
+ // start to Wait()
+ const wxSemaError err = m_semaphore.Wait();
+
m_mutex.Lock();
if ( err == wxSEMA_NO_ERROR )
+ {
+ // m_numWaiters was decremented by Signal()
return wxCOND_NO_ERROR;
- else if ( err == wxSEMA_TIMEOUT )
- return wxCOND_TIMEOUT;
- else
- return wxCOND_MISC_ERROR;
+ }
+
+ // but in case of an error we need to do it manually
+ {
+ wxCriticalSectionLocker lock(m_csWaiters);
+ m_numWaiters--;
+ }
+
+ return err == wxSEMA_TIMEOUT ? wxCOND_TIMEOUT : wxCOND_MISC_ERROR;
}
wxCondError wxConditionInternal::WaitTimeout(unsigned long milliseconds)
m_mutex.Unlock();
- // a race condition can occur at this point in the code
- //
- // please see the comments in Wait(), for details
-
wxSemaError err = m_semaphore.WaitTimeout(milliseconds);
+ m_mutex.Lock();
+
+ if ( err == wxSEMA_NO_ERROR )
+ return wxCOND_NO_ERROR;
+
if ( err == wxSEMA_TIMEOUT )
{
- // another potential race condition exists here it is caused when a
- // 'waiting' thread times out, and returns from WaitForSingleObject,
- // but has not yet decremented m_numWaiters
+ // a potential race condition exists here: it happens when a waiting
+ // thread times out but doesn't have time to decrement m_numWaiters yet
+ // before Signal() is called in another thread
//
- // at this point if another thread calls signal() then the semaphore
- // will be incremented, but the waiting thread will miss it.
- //
- // to handle this particular case, the waiting thread calls
- // WaitForSingleObject again with a timeout of 0, after locking
- // m_csWaiters. This call does not block because of the zero
- // timeout, but will allow the waiting thread to catch the missed
- // signals.
+ // to handle this particular case, check the semaphore again after
+ // acquiring m_csWaiters lock -- this will catch the signals missed
+ // during this window
wxCriticalSectionLocker lock(m_csWaiters);
- wxSemaError err2 = m_semaphore.WaitTimeout(0);
+ err = m_semaphore.WaitTimeout(0);
+ if ( err == wxSEMA_NO_ERROR )
+ return wxCOND_NO_ERROR;
+
+ // we need to decrement m_numWaiters ourselves as it wasn't done by
+ // Signal()
+ m_numWaiters--;
- if ( err2 != wxSEMA_NO_ERROR )
- {
- m_numWaiters--;
- }
+ return err == wxSEMA_TIMEOUT ? wxCOND_TIMEOUT : wxCOND_MISC_ERROR;
}
- m_mutex.Lock();
+ // undo m_numWaiters++ above in case of an error
+ {
+ wxCriticalSectionLocker lock(m_csWaiters);
+ m_numWaiters--;
+ }
- return err == wxSEMA_NO_ERROR ? wxCOND_NO_ERROR
- : err == wxSEMA_TIMEOUT ? wxCOND_TIMEOUT
- : wxCOND_MISC_ERROR;
+ return wxCOND_MISC_ERROR;
}
wxCondError wxConditionInternal::Signal()
wxCondError wxCondition::Wait()
{
wxCHECK_MSG( m_internal, wxCOND_INVALID,
- _T("wxCondition::Wait(): not initialized") );
+ wxT("wxCondition::Wait(): not initialized") );
return m_internal->Wait();
}
wxCondError wxCondition::WaitTimeout(unsigned long milliseconds)
{
wxCHECK_MSG( m_internal, wxCOND_INVALID,
- _T("wxCondition::Wait(): not initialized") );
+ wxT("wxCondition::Wait(): not initialized") );
return m_internal->WaitTimeout(milliseconds);
}
wxCondError wxCondition::Signal()
{
wxCHECK_MSG( m_internal, wxCOND_INVALID,
- _T("wxCondition::Signal(): not initialized") );
+ wxT("wxCondition::Signal(): not initialized") );
return m_internal->Signal();
}
wxCondError wxCondition::Broadcast()
{
wxCHECK_MSG( m_internal, wxCOND_INVALID,
- _T("wxCondition::Broadcast(): not initialized") );
+ wxT("wxCondition::Broadcast(): not initialized") );
return m_internal->Broadcast();
}
wxSemaError wxSemaphore::Wait()
{
wxCHECK_MSG( m_internal, wxSEMA_INVALID,
- _T("wxSemaphore::Wait(): not initialized") );
+ wxT("wxSemaphore::Wait(): not initialized") );
return m_internal->Wait();
}
wxSemaError wxSemaphore::TryWait()
{
wxCHECK_MSG( m_internal, wxSEMA_INVALID,
- _T("wxSemaphore::TryWait(): not initialized") );
+ wxT("wxSemaphore::TryWait(): not initialized") );
return m_internal->TryWait();
}
wxSemaError wxSemaphore::WaitTimeout(unsigned long milliseconds)
{
wxCHECK_MSG( m_internal, wxSEMA_INVALID,
- _T("wxSemaphore::WaitTimeout(): not initialized") );
+ wxT("wxSemaphore::WaitTimeout(): not initialized") );
return m_internal->WaitTimeout(milliseconds);
}
wxSemaError wxSemaphore::Post()
{
wxCHECK_MSG( m_internal, wxSEMA_INVALID,
- _T("wxSemaphore::Post(): not initialized") );
+ wxT("wxSemaphore::Post(): not initialized") );
return m_internal->Post();
}
projects / wxWidgets.git / blobdiff