windows 使用关键段和条件变量实现的生产者和消费者线程同步



关键段比较简单，调用函数如下：

VOID InitializeCriticalSection( LPCRITICAL_SECTION lpCriticalSection );//初始化一个关键代码段

VOID EnterCriticalSection( LPCRITICAL_SECTION lpCriticalSection);//获取关键代码段的访问权

VOID LeaveCriticalSection( LPCRITICAL_SECTION lpCriticalSection);//释放关键代码段的访问权

VOID DeleteCriticalSection( LPCRITICAL_SECTION lpCriticalSection);//删除关键代码段

条件变量的介绍：

Condition variables are synchronization primitives that enable threads to wait until a particular condition occurs. Condition variables are user-mode objects that cannot be shared across processes.

Condition variables enable threads to atomically release a lock and enter the sleeping state. They can be used with critical sections or slim reader/writer (SRW) locks. Condition variables support operations that "wake one" or "wake all" waiting threads. After a thread is woken, it re-acquires the lock it released when the thread entered the sleeping state.

Windows Server 2003 and Windows XP:  Condition variables are not supported.

The following are the condition variable functions.

Condition variable functionDescriptionInitializeConditionVariableInitializes a condition variable.SleepConditionVariableCSSleeps on the specified condition variable and releases the specified critical section as an atomic operation.SleepConditionVariableSRWSleeps on the specified condition variable and releases the specified SRW lock as an atomic operation.WakeAllConditionVariableWakes all threads waiting on the specified condition variable.WakeConditionVariableWakes a single thread waiting on the specified condition variable.

 

The following pseudocode demonstrates the typical usage pattern of condition variables.

CRITICAL_SECTION CritSection;CONDITION_VARIABLE ConditionVar;void PerformOperationOnSharedData(){    EnterCriticalSection(&CritSection);   // Wait until the predicate is TRUE   while( TestPredicate() == FALSE )   {      SleepConditionVariableCS(&ConditionVar, &CritSection, INFINITE);   }   // The data can be changed safely because we own the critical    // section and the predicate is TRUE   ChangeSharedData();   LeaveCriticalSection(&CritSection);   // If necessary, signal the condition variable by calling   // WakeConditionVariable or WakeAllConditionVariable so other   // threads can wake}

The following code implements a producer/consumer queue. The queue is represented as a bounded circular buffer, and is protected by a critical section. The code uses two condition variables: one used by producers (BufferNotFull) and one used by consumers (BufferNotEmpty).

The code calls the InitializeConditionVariable function to create the condition variables. The consumer threads call theSleepConditionVariableCS function to wait for items to be added to the queue and theWakeConditionVariable function to signal the producer that it is ready for more items. The producer threads callSleepConditionVariableCS to wait for the consumer to remove items from the queue andWakeConditionVariable to signal the consumer that there are more items in the queue.

#include <windows.h>#include <stdlib.h>#include <stdio.h>#define BUFFER_SIZE 10#define PRODUCER_SLEEP_TIME_MS 500#define CONSUMER_SLEEP_TIME_MS 2000LONG 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)//等消费完再退出        {            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;}