MSDN 条件变量使用例子

#include <windows.h>
#include <stdlib.h>
#include <stdio.h>

#define BUFFER_SIZE 10
#define PRODUCER_SLEEP_TIME_MS 500
#define CONSUMER_SLEEP_TIME_MS 2000

LONG Buffer[BUFFER_SIZE];
LONG LastItemProduced;
ULONG QueueSize;
ULONG QueueStartOffset;

ULONG TotalItemsProduced;
ULONG TotalItemsConsumed;

CONDITION_VARIABLE BufferNotEmpty;
CONDITION_VARIABLE BufferNotFull;
CRITICAL_SECTION   BufferLock;

BOOL StopRequested;

DWORD WINAPI ProducerThreadProc (PVOID p)
{
ULONG ProducerId = (ULONG)(ULONG_PTR)p;

while (true)
{
// Produce a new item.

Sleep (rand() % PRODUCER_SLEEP_TIME_MS);

ULONG Item = InterlockedIncrement (&LastItemProduced);

EnterCriticalSection (&BufferLock);

while (QueueSize == BUFFER_SIZE && StopRequested == FALSE)
{
// Buffer is full - sleep so consumers can get items.
SleepConditionVariableCS (&BufferNotFull, &BufferLock, INFINITE);
}

if (StopRequested == TRUE)
{
LeaveCriticalSection (&BufferLock);
break;
}

// Insert the item at the end of the queue and increment size.

Buffer[(QueueStartOffset + QueueSize) % BUFFER_SIZE] = Item;
QueueSize++;
TotalItemsProduced++;

printf ("Producer %u: item %2d, queue size %2u\r\n", ProducerId, Item, QueueSize);

LeaveCriticalSection (&BufferLock);

// If a consumer is waiting, wake it.

WakeConditionVariable (&BufferNotEmpty);
}

printf ("Producer %u exiting\r\n", ProducerId);
return 0;
}

DWORD WINAPI ConsumerThreadProc (PVOID p)
{
ULONG ConsumerId = (ULONG)(ULONG_PTR)p;

while (true)
{
EnterCriticalSection (&BufferLock);

while (QueueSize == 0 && StopRequested == FALSE)
{
// Buffer is empty - sleep so producers can create items.
SleepConditionVariableCS (&BufferNotEmpty, &BufferLock, INFINITE);
}

if (StopRequested == TRUE && QueueSize == 0)
{
LeaveCriticalSection (&BufferLock);
break;
}

// Consume the first available item.

LONG Item = Buffer[QueueStartOffset];

QueueSize--;
QueueStartOffset++;
TotalItemsConsumed++;

if (QueueStartOffset == BUFFER_SIZE)
{
QueueStartOffset = 0;
}

printf ("Consumer %u: item %2d, queue size %2u\r\n",
ConsumerId, Item, QueueSize);

LeaveCriticalSection (&BufferLock);

// If a producer is waiting, wake it.

WakeConditionVariable (&BufferNotFull);

// Simulate processing of the item.

Sleep (rand() % CONSUMER_SLEEP_TIME_MS);
}

printf ("Consumer %u exiting\r\n", ConsumerId);
return 0;
}

int main ( void )
{
InitializeConditionVariable (&BufferNotEmpty);
InitializeConditionVariable (&BufferNotFull);

InitializeCriticalSection (&BufferLock);

DWORD id;
HANDLE hProducer1 = CreateThread (NULL, 0, ProducerThreadProc, (PVOID)1, 0, &id);
HANDLE hConsumer1 = CreateThread (NULL, 0, ConsumerThreadProc, (PVOID)1, 0, &id);
HANDLE hConsumer2 = CreateThread (NULL, 0, ConsumerThreadProc, (PVOID)2, 0, &id);

puts ("Press enter to stop...");
getchar();

EnterCriticalSection (&BufferLock);
StopRequested = TRUE;
LeaveCriticalSection (&BufferLock);

WakeAllConditionVariable (&BufferNotFull);
WakeAllConditionVariable (&BufferNotEmpty);

WaitForSingleObject (hProducer1, INFINITE);
WaitForSingleObject (hConsumer1, INFINITE);
WaitForSingleObject (hConsumer2, INFINITE);

printf ("TotalItemsProduced: %u, TotalItemsConsumed: %u\r\n",
TotalItemsProduced, TotalItemsConsumed);
return 0;
}