void ThreadPool::SubmitWork(const StringRef& name)
{
RETURN_IF_EMPTY(name);
ThreadPoolWork* work = FindWork(name);
RETURN_IF_NULL(work);
SubmitWork(*work);
}
/*
* Function: depositWorkItem()
*
* Local function which deposits a WorkItem onto a work queue,
* deciding in the process whether or not the thread pool needs
* to be augmented with another thread to handle the new request.
*
*/
static
int
depositWorkItem( unsigned int reqID,
WorkItem* wItem )
{
EnterCriticalSection(&ioMan->manLock);
#if 0
fprintf(stderr, "depositWorkItem: %d/%d\n",
ioMan->workersIdle, ioMan->numWorkers);
fflush(stderr);
#endif
/* A new worker thread is created when there are fewer idle threads
* than non-consumed queue requests. This ensures that requests will
* be dealt with in a timely manner.
*
* [Long explanation of why the previous thread pool policy lead to
* trouble]
*
* Previously, the thread pool was augmented iff no idle worker threads
* were available. That strategy runs the risk of repeatedly adding to
* the request queue without expanding the thread pool to handle this
* sudden spike in queued requests.
* [How? Assume workersIdle is 1, and addIORequest() is called. No new
* thread is created and the request is simply queued. If addIORequest()
* is called again _before the OS schedules a worker thread to pull the
* request off the queue_, workersIdle is still 1 and another request is
* simply added to the queue. Once the worker thread is run, only one
* request is de-queued, leaving the 2nd request in the queue]
*
* Assuming none of the queued requests take an inordinate amount
* of to complete, the request queue would eventually be
* drained. But if that's not the case, the later requests will
* end up languishing in the queue indefinitely. The non-timely
* handling of requests may cause CH applications to misbehave /
* hang; bad.
*
*/
ioMan->queueSize++;
if ( (ioMan->workersIdle < ioMan->queueSize) ) {
/* see if giving up our quantum ferrets out some idle threads.
*/
LeaveCriticalSection(&ioMan->manLock);
Sleep(0);
EnterCriticalSection(&ioMan->manLock);
if ( (ioMan->workersIdle < ioMan->queueSize) ) {
/* No, go ahead and create another. */
ioMan->numWorkers++;
if (!NewIOWorkerThread(ioMan)) {
ioMan->numWorkers--;
}
}
}
LeaveCriticalSection(&ioMan->manLock);
if (SubmitWork(ioMan->workQueue,wItem)) {
/* Note: the work item has potentially been consumed by a worker thread
* (and freed) at this point, so we cannot use wItem's requestID.
*/
return reqID;
} else {
return 0;
}
}
