WinRequestMutexSem is similar to DosRequestMutexSem and requests ownership of a mutex semaphore or waits for a window message sent by the WinSendMsg function from another thread to be received.

This function can be called by any thread in the process that created the semaphore. Threads in other processes can also call this function, but they must first gain access to the semaphore by issuing DosOpenMutexSem.

Since the processing of a window message may take longer than the value specified by the ulTimeout parameter, this function may not return within the time specified by that value.