Exec provides a variety of useful functions for setting, checking and
freeing semaphores.  The prototypes for these functions are as follows.

    VOID  AddSemaphore ( struct SignalSemaphore *sigSem );
    ULONG AttemptSemaphore( struct SignalSemaphore *sigSem );
    struct SignalSemaphore *FindSemaphore( UBYTE *sigSem );
    VOID InitSemaphore( struct SignalSemaphore *sigSem );

    VOID ObtainSemaphore( struct SignalSemaphore *sigSem );
    VOID ObtainSemaphoreList( struct List *sigSem );
    void ObtainSemaphoreShared( struct SignalSemaphore *sigSem );

    VOID ReleaseSemaphore( struct SignalSemaphore *sigSem );
    VOID ReleaseSemaphoreList( struct List *sigSem );
    VOID RemSemaphore( struct SignalSemaphore *sigSem );

 the signal semaphore    multiple semaphores    semaphore example