Unix to Windows Porting Dictionary for HPC

header file: pthread.h

int pthread_cond_broadcast(pthread_cond_t *cv);

header file: Windows.h

VOID WINAPI WakeAllConditionVariable(
  __inout  PCONDITION_VARIABLE ConditionVariable
);
      

The pthread_cond_broadcast unblocks all threads that are blocked on the condition variable. This call should be made under the protection of the same mutex that is used with the condition variable.

The Windows equivalent function also wakes all of the threads that are waiting on the condition variable. Unlike the POSIX equivalent, it is not necessary to make this call under the protection of the critical section used in the SleepConditionVariableCS call.

This is a simple example of a ring buffer that is controlled by a pair of condition variables that throttle the producer and consumer threads. This same example is also used for the SleepConditionVariableCS and InitializeConditionVariable calls.

#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;
}

void __cdecl wmain (int argc, const wchar_t* argv[])
{
    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);
}