Loop Queue

Queue

// CQueue
//
// Implements a simple Queue ADT.  The queue contains a finite number of
// objects, access to which is controlled by a semaphore.  The semaphore
// is created with an initial count (N).  Each time an object is added
// a call to WaitForSingleObject is made on the semaphore's handle.  When
// this function returns a slot has been reserved in the queue for the new
// object.  If no slots are available the function blocks until one becomes
// available.  Each time an object is removed from the queue ReleaseSemaphore
// is called on the semaphore's handle, thus freeing a slot in the queue.
// If no objects are present in the queue the function blocks until an
// object has been added.

#define DEFAULT_QUEUESIZE   2

template <class T> class CQueue {
private:
    HANDLE          hSemPut;        // Semaphore controlling queue "putting"
    HANDLE          hSemGet;        // Semaphore controlling queue "getting"
    CRITICAL_SECTION CritSect;      // Thread seriallization
    int             nMax;           // Max objects allowed in queue
    int             iNextPut;       // Array index of next "PutMsg"
    int             iNextGet;       // Array index of next "GetMsg"
    T              *QueueObjects;   // Array of objects (ptr's to void)

    void Initialize(int n) {
        iNextPut = iNextGet = 0;
        nMax = n;
        InitializeCriticalSection(&CritSect);
        hSemPut = CreateSemaphore(NULL, n, n, NULL);
        hSemGet = CreateSemaphore(NULL, 0, n, NULL);
        QueueObjects = new T[n];
    }


public:
    CQueue(int n) {
        Initialize(n);
    }

    CQueue() {
        Initialize(DEFAULT_QUEUESIZE);
    }

    ~CQueue() {
        delete [] QueueObjects;
        DeleteCriticalSection(&CritSect);
        CloseHandle(hSemPut);
        CloseHandle(hSemGet);
    }

    T GetQueueObject() {
        int iSlot;
        T Object;
        LONG lPrevious;

        // Wait for someone to put something on our queue, returns straight
        // away is there is already an object on the queue.
        //
        WaitForSingleObject(hSemGet, INFINITE);

        EnterCriticalSection(&CritSect);
        iSlot = iNextGet++ % nMax;
        Object = QueueObjects[iSlot];
        LeaveCriticalSection(&CritSect);

        // Release anyone waiting to put an object onto our queue as there
        // is now space available in the queue.
        //
        ReleaseSemaphore(hSemPut, 1L, &lPrevious);
        return Object;
    }

    void PutQueueObject(T Object) {
        int iSlot;
        LONG lPrevious;

        // Wait for someone to get something from our queue, returns straight
        // away is there is already an empty slot on the queue.
        //
        WaitForSingleObject(hSemPut, INFINITE);

        EnterCriticalSection(&CritSect);
        iSlot = iNextPut++ % nMax;
        QueueObjects[iSlot] = Object;
        LeaveCriticalSection(&CritSect);

        // Release anyone waiting to remove an object from our queue as there
        // is now an object available to be removed.
        //
        ReleaseSemaphore(hSemGet, 1L, &lPrevious);
    }
};