SignalObjectAndWait

The SignalObjectAndWait function allows the caller to atomically signal an object and wait on another object.

DWORD SignalObjectAndWait(
  HANDLE hObjectToSignal,  // handle to object to signal
  HANDLE hObjectToWaitOn,  // handle to object to watch
  DWORD dwMilliseconds,    // time-out interval
  BOOL bAlertable          // alertable option
);

Parameters

hObjectToSignal

[in] Specifies the handle to the object to signal. This object can be a semaphore, a mutex, or an event.

Windows NT/2000: If the handle is a semaphore, SEMAPHORE_MODIFY_STATE access is required. If the handle is an event, EVENT_MODIFY_STATE access is required. If the handle is a mutex, SYNCHRONIZE access is assumed, because only the owner of a mutex may release it. For more information, see Synchronization Object Security and Access Rights.

hObjectToWaitOn

[in] Specifies the handle to the object to wait for. For a list of the object types whose handles you can specify, see the Remarks section.

dwMilliseconds

[in] Specifies the time-out interval, in milliseconds. The function returns if the interval elapses, even if the object's state is nonsignaled and no completion or asynchronous procedure call (APC) objects are queued. If dwMilliseconds is zero, the function tests the object's state, checks for queued completion routines or APCs, and returns immediately. If dwMilliseconds is INFINITE, the function's time-out interval never elapses.

bAlertable

[in] Specifies whether the function returns when the system queues an I/O completion routine or an APC for the calling thread. If TRUE, the function returns and the thread calls the completion routine or APC function. If FALSE, the function does not return, and the thread does not call the completion routine or APC function.

A completion routine is queued when the ReadFileEx or WriteFileEx function in which it was specified has completed. The wait function returns and the completion routine is called only if bAlertable is TRUE, and the calling thread is the thread that initiated the read or write operation. An APC is queued when you call QueueUserAPC.

Return Values

If the function succeeds, the return value indicates the event that caused the function to return. This value can be one of the following:

If the function fails, the return value is -1. To get extended error information, call GetLastError.

Remarks

A completion routine is queued for execution when the ReadFileEx or WriteFileEx function in which it was specified has been completed. The wait function returns and the completion routine is executed only if bAlertable is TRUE, and the calling thread is the thread that initiated the read or write operation.

The SignalObjectAndWait function can wait for the following objects:

• Change notification
• Console input
• Event
• Job
• Mutex
• Process
• Semaphore
• Thread
• Waitable timer

For more information, see Synchronization Objects.

Use caution when using the wait functions and code that directly or indirectly creates windows. If a thread creates any windows, it must process messages. Message broadcasts are sent to all windows in the system. A thread that uses a wait function with no time-out interval may cause the system to become deadlocked. Two examples of code that indirectly creates windows are DDE and COM CoInitialize. Therefore, if you have a thread that creates windows, use MsgWaitForMultipleObjects or MsgWaitForMultipleObjectsEx, rather than SignalObjectAndWait.

Requirements

  Windows NT/2000: Requires Windows NT 4.0 or later.
  Windows 95/98: Unsupported.
  Header: Declared in Winbase.h; include Windows.h.
  Library: Use Kernel32.lib.

See Also

Synchronization Overview, Synchronization Functions, MsgWaitForMultipleObjects, MsgWaitForMultipleObjectsEx