DosSemWait

Bindings:  C, MASM 

This call blocks the current thread until an indicated semaphore clears, 
but does not establish ownership of the semaphore. 

 DosSemWait    (SemHandle, Timeout) 
 

 SemHandle (HSEM) - input 
    Reference to the semaphore. 

    For a system semaphore, this reference is the handle returned by a 
    DosCreateSem or DosOpenSem request that granted the requesting thread 
    access to the semaphore. 

    For a RAM semaphore, this reference is the address of a doubleword of 
    storage, allocated and initialized to zero by the application. This 
    sets the semaphore as unowned. Other than initializing the doubleword 
    to zero, an application must not modify a RAM semaphore directly; 
    instead it manipulates the semaphore with semaphore function calls. 

 Timeout (LONG) - input 
    Action taken by the requesting thread when the semaphore is set. The 
    values that can be specified are: 

    Value     Definition 
     -1       The requesting thread waits indefinitely for the semaphore 
              to be cleared. 
      0       The requesting thread returns immediately. 
     > 0      The requesting thread waits the indicated number of 
              milliseconds for the semaphore to be cleared before resuming 
              execution. 

 rc (USHORT) - return 
    Return code descriptions are: 

    0         NO_ERROR 
    95        ERROR_INTERRUPT 
    121       ERROR_SEM_TIMEOUT 
 
 Remarks 

 The unblocking of a thread blocked by a DosSemWait is level-triggered. 
 That is, DosSemWait does not return until the semaphore remains clear 
 long enough for the affected thread to be redispatched and determine that 
 the semaphore is clear. 

 When an application needs to guarantee that another event has occurred 
 before continuing, it calls DosSemSetWait. DosSemSetWait combines the 
 functions of DosSemSet and  DosSemWait and is used when there is a chance 
 the semaphore may be cleared by a thread that gets an intervening time 
 slice between calls by the current thread to set the semaphore and wait 
 until it is cleared. Issuing DosSemWait on a semaphore that has been 
 cleared has no effect; the thread continues to execute.