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one more correction to wxCondition::WaitTimeout() return code: don't overwrite err with the semaphore wait result (bug 1387179)

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git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@42206 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
This commit is contained in:
Vadim Zeitlin 2006-10-21 16:06:11 +00:00
parent 4cbc928afc
commit e7e9ac91c2
1 changed files with 9 additions and 9 deletions
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18
include/wx/thrimpl.cpp
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@ -116,12 +116,12 @@ wxCondError wxConditionInternal::Wait()
// a potential race condition can occur here
//
// after a thread increments nwaiters, and unlocks the mutex and before the
// semaphore.Wait() is called, if another thread can cause a signal to be
// generated
// 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 'nwaiters' is greater that zero since the semaphore,
// 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
@ -154,22 +154,22 @@ wxCondError wxConditionInternal::WaitTimeout(unsigned long milliseconds)
if ( err == wxSEMA_TIMEOUT )
{
// another potential race condition exists here it is caused when a
// 'waiting' thread timesout, and returns from WaitForSingleObject, but
// has not yet decremented 'nwaiters'.
// 'waiting' thread times out, and returns from WaitForSingleObject,
// but has not yet decremented m_numWaiters
//
// 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
// 'nwaiters_mutex'. this call does not block because of the zero
// m_csWaiters. This call does not block because of the zero
// timeout, but will allow the waiting thread to catch the missed
// signals.
wxCriticalSectionLocker lock(m_csWaiters);
err = m_semaphore.WaitTimeout(0);
wxSemaError err2 = m_semaphore.WaitTimeout(0);
if ( err != wxSEMA_NO_ERROR )
if ( err2 != wxSEMA_NO_ERROR )
{
m_numWaiters--;
}