DosSemWait

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:
• 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.

  ---

  [Back: DosSemSetWait]
  [Next: DosSendSignal]