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/*
* A fixed-size queue; MT-friendly.
*
* (c) sof, 2002-2003.
*/
#include "WorkQueue.h"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
static void queue_error_rc( char* loc, DWORD err);
static void queue_error( char* loc, char* reason);
/* Wrapper around OS call to create semaphore */
static Semaphore
newSemaphore(int initCount, int max)
{
Semaphore s;
s = CreateSemaphore ( NULL, /* LPSECURITY_ATTRIBUTES (default) */
initCount, /* LONG lInitialCount */
max, /* LONG lMaxCount */
NULL); /* LPCTSTR (anonymous / no object name) */
if ( NULL == s) {
queue_error_rc("newSemaphore", GetLastError());
return NULL;
}
return s;
}
/*
* Function: NewWorkQueue
*
* The queue constructor - semaphores are initialised to match
* max number of queue entries.
*
*/
WorkQueue*
NewWorkQueue()
{
WorkQueue* wq = (WorkQueue*)malloc(sizeof(WorkQueue));
if (!wq) {
queue_error("NewWorkQueue", "malloc() failed");
return wq;
}
memset(wq, 0, sizeof *wq);
InitializeCriticalSection(&wq->queueLock);
wq->workAvailable = newSemaphore(0, WORKQUEUE_SIZE);
wq->roomAvailable = newSemaphore(WORKQUEUE_SIZE, WORKQUEUE_SIZE);
/* Fail if we were unable to create any of the sync objects. */
if ( NULL == wq->workAvailable ||
NULL == wq->roomAvailable ) {
FreeWorkQueue(wq);
return NULL;
}
return wq;
}
void
FreeWorkQueue ( WorkQueue* pq )
{
int i;
/* Free any remaining work items. */
for (i = 0; i < WORKQUEUE_SIZE; i++) {
if (pq->items[i] != NULL) {
free(pq->items[i]);
}
}
/* Close the semaphores; any threads blocked waiting
* on either will as a result be woken up.
*/
if ( pq->workAvailable ) {
CloseHandle(pq->workAvailable);
}
if ( pq->roomAvailable ) {
CloseHandle(pq->roomAvailable);
}
DeleteCriticalSection(&pq->queueLock);
free(pq);
return;
}
HANDLE
GetWorkQueueHandle ( WorkQueue* pq )
{
if (!pq) return NULL;
return pq->workAvailable;
}
/*
* Function: GetWork
*
* Fetch a work item from the queue, blocking if none available.
* Return value indicates of FALSE indicates error/fatal condition.
*/
BOOL
GetWork ( WorkQueue* pq, void** ppw )
{
DWORD rc;
if (!pq) {
queue_error("GetWork", "NULL WorkQueue object");
return FALSE;
}
if (!ppw) {
queue_error("GetWork", "NULL WorkItem object");
return FALSE;
}
/* Block waiting for work item to become available */
if ( (rc = WaitForSingleObject( pq->workAvailable, INFINITE))
!= WAIT_OBJECT_0 ) {
queue_error_rc("GetWork.WaitForSingleObject(workAvailable)",
( (WAIT_FAILED == rc) ? GetLastError() : rc));
return FALSE;
}
return FetchWork(pq,ppw);
}
/*
* Function: FetchWork
*
* Fetch a work item from the queue, blocking if none available.
* Return value indicates of FALSE indicates error/fatal condition.
*/
BOOL
FetchWork ( WorkQueue* pq, void** ppw )
{
DWORD rc;
if (!pq) {
queue_error("FetchWork", "NULL WorkQueue object");
return FALSE;
}
if (!ppw) {
queue_error("FetchWork", "NULL WorkItem object");
return FALSE;
}
EnterCriticalSection(&pq->queueLock);
*ppw = pq->items[pq->head];
/* For sanity's sake, zero out the pointer. */
pq->items[pq->head] = NULL;
pq->head = (pq->head + 1) % WORKQUEUE_SIZE;
rc = ReleaseSemaphore(pq->roomAvailable,1, NULL);
LeaveCriticalSection(&pq->queueLock);
if ( 0 == rc ) {
queue_error_rc("FetchWork.ReleaseSemaphore()", GetLastError());
return FALSE;
}
return TRUE;
}
/*
* Function: SubmitWork
*
* Add work item to the queue, blocking if no room available.
* Return value indicates of FALSE indicates error/fatal condition.
*/
BOOL
SubmitWork ( WorkQueue* pq, void* pw )
{
DWORD rc;
if (!pq) {
queue_error("SubmitWork", "NULL WorkQueue object");
return FALSE;
}
if (!pw) {
queue_error("SubmitWork", "NULL WorkItem object");
return FALSE;
}
/* Block waiting for work item to become available */
if ( (rc = WaitForSingleObject( pq->roomAvailable, INFINITE))
!= WAIT_OBJECT_0 ) {
queue_error_rc("SubmitWork.WaitForSingleObject(workAvailable)",
( (WAIT_FAILED == rc) ? GetLastError() : rc));
return FALSE;
}
EnterCriticalSection(&pq->queueLock);
pq->items[pq->tail] = pw;
pq->tail = (pq->tail + 1) % WORKQUEUE_SIZE;
rc = ReleaseSemaphore(pq->workAvailable,1, NULL);
LeaveCriticalSection(&pq->queueLock);
if ( 0 == rc ) {
queue_error_rc("SubmitWork.ReleaseSemaphore()", GetLastError());
return FALSE;
}
return TRUE;
}
/* Error handling */
static void
queue_error_rc( char* loc,
DWORD err)
{
fprintf(stderr, "%s failed: return code = 0x%lx\n", loc, err);
fflush(stderr);
return;
}
static void
queue_error( char* loc,
char* reason)
{
fprintf(stderr, "%s failed: %s\n", loc, reason);
fflush(stderr);
return;
}
// Local Variables:
// mode: C
// fill-column: 80
// indent-tabs-mode: nil
// c-basic-offset: 4
// buffer-file-coding-system: utf-8-unix
// End:
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