If a process manages only one queue, it typically waits for an element to become available. However, if a process manages several queues, waiting for one queue means that other queues cannot be read. To avoid wasting time while waiting, a process can supply an event semaphore when it calls DosReadQueue or DosPeekQueue. The process can then continue to execute without actually reading an element from the queue, because DosWriteQueue will post the semaphore only when an element is ready. The semaphore remains posted until someone resets it; usually the queue owner process resets the semaphore after it reads all the available information from the queue.

If a process uses a unique semaphore for each queue, it can use DosWaitMuxWaitSem to wait for the first queue to receive an element.

Only one semaphore is permitted per queue.