SignalObjectAndWait info  Overview  Group

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

DWORD SignalObjectAndWait(

Parameters

hObjectToSignal

Specifies the handle to the object to signal. This object can be a semaphore, a mutex, or an event. 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 Interprocess Synchronization Objects.

hObjectToWaitOn

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

dwMilliseconds

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

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.

If the function fails, the return value is 0xFFFFFFFF. To get extended error information, call GetLastError.

Upon success, the return value is one of the following values:

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:

Wait Functions and Creating Windows

You have to be careful 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. If you have a thread that uses a wait function with no time-out interval, the system will deadlock. 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.

See Also

CancelWaitableTimer, CreateEvent, CreateMutex, CreateProcess, CreateThread, CreateRemoteThread, CreateSemaphore, CreateWaitableTimer, FindFirstChangeNotification, MsgWaitForMultipleObjects, MsgWaitForMultipleObjectsEx, OpenEvent, OpenMutex, OpenProcess, OpenSemaphore, OpenWaitableTimer, PulseEvent, QueueUserAPC, ReadFileEx, ResetEvent, SetEvent, SetWaitableTimer, WriteFileEx

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