An application uses DosAddMuxWaitSem to add semaphores to a muxwait semaphore that has already been created, even while threads are waiting on the muxwait semaphore.
Any thread in the process that created a muxwait semaphore can add a mutex semaphore or an event semaphore to the muxwait list by calling DosAddMuxWaitSem. Threads in other processes can also use this function, but they must first gain access to the semaphore by calling DosOpenMuxWaitSem.
A maximum of 64 semaphores can be included in a muxwait-semaphore list. If an attempt is made to exceed this maximum, ERROR_TOO_MANY_SEMAPHORES is returned.
All of the semaphores in a muxwait-semaphore list must be of the same type. That is, if a mutex semaphore is being added, then the other semaphores in the list must be mutex semaphores. If an event semaphore is being added, then the other semaphores in the list must be event semaphores. A shared muxwait semaphore can contain only shared semaphores in its list. A private muxwait semaphore can contain both private and shared semaphores. If any of these conditions is violated, ERROR_WRONG_TYPE is returned.
If the semaphore is successfully added to the muxwait list, DosAddMuxWaitSem checks to see whether each thread that is waiting for the muxwait semaphore has the newly added semaphore open in its process. The muxwait semaphore is invalid for any waiting threads that do not have the newly added semaphore open in their process; these threads are unblocked with a return code of ERROR_INVALID_HANDLE. Any processes that opened the muxwait semaphore before the add operation and that do not have the new semaphore open, will have to open the new semaphore before making any further use of the muxwait semaphore. Any future calls concerning the muxwait semaphore by processes that do not have the new semaphore open will have ERROR_INVALID_HANDLE returned until the new semaphore is opened.
A thread that receives a return code of ERROR_INVALID_HANDLE can take the following corrective action:
As soon as this semaphore is opened, the muxwait semaphore becomes valid again for the process, as long as no other changes have been made to the muxwait list to make it invalid. However, in order to successfully wait for the muxwait semaphore, the process must call DosWaitMuxWaitSem again.
A semaphore must be open for a process before the process can add that semaphore to a muxwait semaphore. If it is not open and a thread is waiting on the muxwait semaphore, DosAddMuxWaitSem returns ERROR_INVALID_HANDLE to the process adding the new semaphore, and the waiting thread continues waiting.