Unix to Windows Porting Dictionary for HPC

header file: pthread.h

int pthread_cond_init(pthread_cond_t *cv, const pthread_condattr_t *cattr);

header file: Windows.h

VOID WINAPI InitializeConditionVariable(
  __out  PCONDITION_VARIABLE ConditionVariable
);
      

The pthread_cond_init initializes a condition variable. The attributes are set to the default if the pointer to condattr is NULL.

The Windows equivalent function is effectively the same as the POSIX version. This creates the condition variable and sets it to the default attributes.

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 WakeConditionVariable and SleepConditionVariableCS 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);
}