SleepConditionVariableCS will hang - c++

Question

I modified the "Using Condition Variables" example in MSDN. I created several threads, which have their own producer/consumer separately.
But the program will often hang when attached to debugger. It always hangs at SleepConditionVariableCS. When I break all and continue in debugger, the program will continue to run. I found that WakeAllConditionVariable didn't wake up some thread calls SleepConditionVariableCS, for the Ptr in PExecutingTask->BufferNotFull or PExecutingTask->BufferNotEmpty was already 0x00000000(I thought that means the condition variable is wakened).
When not attached to debugger, the program will not hang.
Has anyone encountered this problem before? How to solve it?
Here is the code:
#include <windows.h>
#include <stdlib.h>
#include <stdio.h>
#define BUFFER_SIZE 100
DWORD WINAPI ProducerThreadProc (PVOID p);
DWORD WINAPI ConsumerThreadProc (PVOID p);
class ExecutingTask
{
public:
void Initialize()
{
InitializeConditionVariable (&BufferNotEmpty);
InitializeConditionVariable (&BufferNotFull);
InitializeCriticalSection (&BufferLock);
QueueSize = 0;
StopRequested = FALSE;
hProducer = CreateThread(NULL, 0, ProducerThreadProc, (PVOID)this, 0, NULL);
for (int i = 0; i < 20; i++)
{
PhConsumers[i] = CreateThread (NULL, 0, ConsumerThreadProc, (PVOID)this, 0, NULL);
}
}
void Stop()
{
EnterCriticalSection (&BufferLock);
StopRequested = TRUE;
LeaveCriticalSection (&BufferLock);
WakeAllConditionVariable (&BufferNotFull);
WakeAllConditionVariable (&BufferNotEmpty);
WaitForSingleObject(hProducer, INFINITE);
WaitForMultipleObjects(20, (HANDLE *)&PhConsumers, true, INFINITE);
CloseHandle(hProducer);
for (unsigned int i = 0; i < 20; i++)
{
CloseHandle(PhConsumers[i]);
}
}
public:
ULONG QueueSize;
CONDITION_VARIABLE BufferNotEmpty;
CONDITION_VARIABLE BufferNotFull;
CRITICAL_SECTION BufferLock;
BOOL StopRequested;
HANDLE PhConsumers[20];
HANDLE hProducer;
};
DWORD WINAPI ProducerThreadProc (PVOID p)
{
ExecutingTask* PExecutingTask = (ExecutingTask*)p;
while (true)
{
EnterCriticalSection (&PExecutingTask->BufferLock);
while (PExecutingTask->QueueSize >= BUFFER_SIZE && PExecutingTask->StopRequested == FALSE)
{
// Buffer is full - sleep so consumers can get items.
SleepConditionVariableCS (&PExecutingTask->BufferNotFull, &PExecutingTask->BufferLock, INFINITE);
}
if (PExecutingTask->StopRequested == TRUE)
{
LeaveCriticalSection (&PExecutingTask->BufferLock);
break;
}
// Produce an item.
PExecutingTask->QueueSize++;
LeaveCriticalSection (&PExecutingTask->BufferLock);
WakeConditionVariable (&PExecutingTask->BufferNotEmpty);
}
return 0;
}
DWORD WINAPI ConsumerThreadProc (PVOID p)
{
ExecutingTask* PExecutingTask = (ExecutingTask*)p;
while (true)
{
EnterCriticalSection (&PExecutingTask->BufferLock);
while (PExecutingTask->QueueSize == 0 && PExecutingTask->StopRequested == FALSE)
{
// Buffer is empty - sleep so producers can create items.
SleepConditionVariableCS (&PExecutingTask->BufferNotEmpty, &PExecutingTask->BufferLock, INFINITE);
}
if (PExecutingTask->StopRequested == TRUE)
{
LeaveCriticalSection (&PExecutingTask->BufferLock);
break;
}
// Consume an item.
PExecutingTask->QueueSize--;
LeaveCriticalSection (&PExecutingTask->BufferLock);
WakeConditionVariable (&PExecutingTask->BufferNotFull);
}
return 0;
}
DWORD WINAPI ThreadProc (PVOID p)
{
ExecutingTask task;
task.Initialize();
Sleep(1000);
task.Stop();
printf ("%u exit\n", &task);
return 0;
};
int main ( void )
{
HANDLE hTaskThreads[50];
for (int i = 0; i < 50; i++)
{
hTaskThreads[i] = CreateThread (NULL, 0, ThreadProc, NULL, 0, NULL);
}
WaitForMultipleObjects(50, hTaskThreads, true, INFINITE);
for (int i = 0; i < 50; i++)
{
CloseHandle(hTaskThreads[i]);
}
}