X-Git-Url: https://git.saurik.com/wxWidgets.git/blobdiff_plain/696d13ee0e378e3f14eb624cae2335bc05f74d06..a9a2485d6464928fcf1012e573f4b3b734238300:/include/wx/thrimpl.cpp diff --git a/include/wx/thrimpl.cpp b/include/wx/thrimpl.cpp index 63b837fec6..6664ce7ee4 100644 --- a/include/wx/thrimpl.cpp +++ b/include/wx/thrimpl.cpp @@ -101,7 +101,7 @@ private: wxMutex& m_mutex; wxSemaphore m_semaphore; - DECLARE_NO_COPY_CLASS(wxConditionInternal) + wxDECLARE_NO_COPY_CLASS(wxConditionInternal); }; wxConditionInternal::wxConditionInternal(wxMutex& mutex) @@ -122,26 +122,27 @@ wxCondError wxConditionInternal::Wait() 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) @@ -153,41 +154,42 @@ 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() @@ -336,3 +338,13 @@ wxSemaError wxSemaphore::Post() return m_internal->Post(); } +// ---------------------------------------------------------------------------- +// wxThread +// ---------------------------------------------------------------------------- + +#include "wx/utils.h" + +void wxThread::Sleep(unsigned long milliseconds) +{ + wxMilliSleep(milliseconds); +}