void MiscThreadTestCase::TestThreadSuspend()
{
MyDetachedThread *thread = new MyDetachedThread(15, 'X');
CPPUNIT_ASSERT_EQUAL( wxTHREAD_NO_ERROR, thread->Run() );
// this is for this demo only, in a real life program we'd use another
// condition variable which would be signaled from wxThread::Entry() to
// tell us that the thread really started running - but here just wait a
// bit and hope that it will be enough (the problem is, of course, that
// the thread might still not run when we call Pause() which will result
// in an error)
wxMilliSleep(300);
for ( size_t n = 0; n < 3; n++ )
{
thread->Pause();
if ( n > 0 )
{
// don't sleep but resume immediately the first time
wxMilliSleep(300);
}
CPPUNIT_ASSERT_EQUAL( wxTHREAD_NO_ERROR, thread->Resume() );
}
// wait until the thread terminates
CPPUNIT_ASSERT_EQUAL( wxSEMA_NO_ERROR, gs_cond.Wait() );
}
void wxThreadInternal::Resume()
{
wxCHECK_RET( m_state == STATE_PAUSED,
wxT("can't resume thread which is not suspended.") );
// the thread might be not actually paused yet - if there were no call to
// TestDestroy() since the last call to Pause() for example
if ( IsReallyPaused() )
{
wxLogTrace(TRACE_THREADS,
_T("Waking up thread %ld"), THR_ID(this));
// wake up Pause()
m_semSuspend.Post();
// reset the flag
SetReallyPaused(false);
}
else
{
wxLogTrace(TRACE_THREADS,
_T("Thread %ld is not yet really paused"), THR_ID(this));
}
SetState(STATE_RUNNING);
}
wxCondError wxConditionInternal::Wait()
{
// increment the number of waiters
{
wxCriticalSectionLocker lock(m_csWaiters);
m_numWaiters++;
}
m_mutex.Unlock();
// 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;
}
// 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;
}
void MyDetachedThread::OnExit()
{
//wxLogTrace(wxT("thread"), wxT("Thread %ld is in OnExit"), GetId());
wxCriticalSectionLocker lock(gs_critsect);
if ( !--gs_counter && !m_cancelled )
gs_cond.Post();
}
wxCondError wxConditionInternal::WaitTimeout(unsigned long milliseconds)
{
{
wxCriticalSectionLocker lock(m_csWaiters);
m_numWaiters++;
}
m_mutex.Unlock();
wxSemaError err = m_semaphore.WaitTimeout(milliseconds);
m_mutex.Lock();
if ( err == wxSEMA_NO_ERROR )
return wxCOND_NO_ERROR;
if ( err == wxSEMA_TIMEOUT )
{
// 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
//
// 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);
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--;
return err == wxSEMA_TIMEOUT ? wxCOND_TIMEOUT : wxCOND_MISC_ERROR;
}
// undo m_numWaiters++ above in case of an error
{
wxCriticalSectionLocker lock(m_csWaiters);
m_numWaiters--;
}
return wxCOND_MISC_ERROR;
}
void wxThreadInternal::Pause()
{
// the state is set from the thread which pauses us first, this function
// is called later so the state should have been already set
wxCHECK_RET( m_state == STATE_PAUSED,
wxT("thread must first be paused with wxThread::Pause().") );
// wait until the semaphore is Post()ed from Resume()
m_semSuspend.Wait();
}
wxCondError wxConditionInternal::WaitTimeout( unsigned long milliseconds )
{
IncrementAtomic( &m_numWaiters );
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);
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'.
//
// 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
// timeout, but will allow the waiting thread to catch the missed
// signals.
wxCriticalSectionLocker lock(m_csWaiters);
err = m_semaphore.WaitTimeout(0);
if ( err != wxSEMA_NO_ERROR )
{
m_numWaiters--;
}
}
m_mutex.Lock();
return err == wxSEMA_NO_ERROR ? wxCOND_NO_ERROR : wxCOND_MISC_ERROR;
}
void MiscThreadTestCase::TestThreadConditions()
{
wxMutex mutex;
wxCondition condition(mutex);
// otherwise its difficult to understand which log messages pertain to
// which condition
//wxLogTrace(wxT("thread"), wxT("Local condition var is %08x, gs_cond = %08x"),
// condition.GetId(), gs_cond.GetId());
// create and launch threads
MyWaitingThread *threads[10];
size_t n;
for ( n = 0; n < WXSIZEOF(threads); n++ )
{
threads[n] = new MyWaitingThread( &mutex, &condition );
}
for ( n = 0; n < WXSIZEOF(threads); n++ )
{
CPPUNIT_ASSERT_EQUAL( wxTHREAD_NO_ERROR, threads[n]->Run() );
}
// wait until all threads run
// NOTE: main thread is waiting for the other threads to start
size_t nRunning = 0;
while ( nRunning < WXSIZEOF(threads) )
{
CPPUNIT_ASSERT_EQUAL( wxSEMA_NO_ERROR, gs_cond.Wait() );
nRunning++;
// note that main thread is already running
}
wxMilliSleep(500);
#if 1
// now wake one of them up
CPPUNIT_ASSERT_EQUAL( wxCOND_NO_ERROR, condition.Signal() );
#endif
wxMilliSleep(200);
// wake all the (remaining) threads up, so that they can exit
CPPUNIT_ASSERT_EQUAL( wxCOND_NO_ERROR, condition.Broadcast() );
// give them time to terminate (dirty!)
wxMilliSleep(500);
}
wxCondError wxConditionInternal::Broadcast()
{
wxCriticalSectionLocker lock(m_csWaiters);
while ( m_numWaiters > 0 )
{
if ( m_semaphore.Post() != wxSEMA_NO_ERROR )
return wxCOND_MISC_ERROR;
m_numWaiters--;
}
return wxCOND_NO_ERROR;
}
virtual ExitCode Entry()
{
//wxPrintf(wxT("Thread %lu has started running.\n"), GetId());
gs_cond.Post();
//wxPrintf(wxT("Thread %lu starts to wait...\n"), GetId());
m_mutex->Lock();
m_condition->Wait();
m_mutex->Unlock();
//wxPrintf(wxT("Thread %lu finished to wait, exiting.\n"), GetId());
return 0;
}
wxCondError wxConditionInternal::Signal()
{
wxCriticalSectionLocker lock(m_csWaiters);
if ( m_numWaiters > 0 )
{
// increment the semaphore by 1
if ( m_semaphore.Post() != wxSEMA_NO_ERROR )
return wxCOND_MISC_ERROR;
m_numWaiters--;
}
return wxCOND_NO_ERROR;
}
void wxThreadInternal::Resume()
{
wxCHECK_RET( m_state == STATE_PAUSED,
wxT("can't resume thread which is not suspended.") );
// the thread might be not actually paused yet - if there were no call to
// TestDestroy() since the last call to Pause() for example
if ( IsReallyPaused() )
{
// wake up Pause()
m_semSuspend.Post();
// reset the flag
SetReallyPaused( false );
}
SetState( STATE_RUNNING );
}
void MiscThreadTestCase::TestDetached()
{
static const size_t nThreads = 3;
MyDetachedThread *threads[nThreads];
size_t n;
for ( n = 0; n < nThreads; n++ )
{
threads[n] = new MyDetachedThread(10, 'A' + n);
}
threads[0]->SetPriority(WXTHREAD_MIN_PRIORITY);
threads[1]->SetPriority(WXTHREAD_MAX_PRIORITY);
for ( n = 0; n < nThreads; n++ )
{
CPPUNIT_ASSERT_EQUAL( wxTHREAD_NO_ERROR, threads[n]->Run() );
}
// wait until all threads terminate
CPPUNIT_ASSERT_EQUAL( wxSEMA_NO_ERROR, gs_cond.Wait() );
}
wxCondError wxConditionInternal::Wait()
{
// increment the number of waiters
IncrementAtomic( &m_numWaiters );
m_mutex.Unlock();
// 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
//
// this race condition is handled by using a semaphore and incrementing the
// semaphore only if 'nwaiters' 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();
m_mutex.Lock();
return err == wxSEMA_NO_ERROR ? wxCOND_NO_ERROR : wxCOND_MISC_ERROR;
}
wxCondError wxConditionInternal::Broadcast()
{
wxCriticalSectionLocker lock(m_csWaiters);
#if defined(__INTEL_COMPILER) && 1 /* VDM auto patch */
# pragma ivdep
# pragma swp
# pragma unroll
# pragma prefetch
# if 0
# pragma simd noassert
# endif
#endif /* VDM auto patch */
while ( m_numWaiters > 0 )
{
if ( m_semaphore.Post() != wxSEMA_NO_ERROR )
return wxCOND_MISC_ERROR;
m_numWaiters--;
}
return wxCOND_NO_ERROR;
}
