MsgWaitForMultipleObjectsEx info  Overview  Group

The MsgWaitForMultipleObjectsEx function returns when one of the following occurs:

• Either any one or all of the specified objects are in the signaled state. The array of objects can include input event objects, which you specify using the dwWakeMask parameter.

• An I/O completion routine or asynchronous procedure call (APC) is queued to the thread.

• The time-out interval elapses.

Note that MsgWaitForMultipleObjectsEx does not return if there is unread input of the specified type in the message queue after the thread has called a function to check the queue. This is because functions such as PeekMessage, GetMessage, WaitMessage, MsgWaitForMultipleObjects, and MsgWaitForMultipleObjectsEx check the queue and then change the state information for the queue so that the input is no longer considered new. A subsequent call to MsgWaitForMultipleObjectsEx will not return until new input of the specified type arrives. The existing unread input is ignored.

DWORD MsgWaitForMultipleObjectsEx(

Parameters

nCount

Specifies the number of object handles in the array pointed to by pHandles. The maximum number of object handles is MAXIMUM_WAIT_OBJECTS minus one.

pHandles

Points to an array of object handles. For a list of the object types whose handles you can specify, see the Remarks section later in this topic. The array can contain handles to multiple types of objects.

Windows NT: The handles must have SYNCHRONIZE access.

dwMilliseconds

Specifies the time-out interval, in milliseconds. The function returns if the interval elapses, even if the conditions specified by the dwWakeMask and dwFlags parameters are not met. If dwMilliseconds is zero, the function tests the states of the specified objects and returns immediately. If dwMilliseconds is INFINITE, the function's time-out interval never elapses.

dwWakeMask

Specifies input types for which an input event object handle will be added to the array of object handles. This parameter can be any combination of the following values:

Value	Meaning
QS_ALLINPUT	Any message is in the queue.
QS_HOTKEY	A WM_HOTKEY message is in the queue.
QS_INPUT	An input message is in the queue.
QS_KEY	A WM_KEYUP, WM_KEYDOWN, WM_SYSKEYUP, or WM_SYSKEYDOWN message is in the queue.
QS_MOUSE	A WM_MOUSEMOVE message or mouse-button message (WM_LBUTTONUP, WM_RBUTTONDOWN, and so on) is in the queue.
QS_MOUSEBUTTON	A mouse-button message (WM_LBUTTONUP, WM_RBUTTONDOWN, and so on) is in the queue.
QS_MOUSEMOVE	A WM_MOUSEMOVE message is in the queue.
QS_PAINT	A WM_PAINT message is in the queue.
QS_POSTMESSAGE	A posted message (other than those just listed) is in the queue.
QS_SENDMESSAGE	A message sent by another thread or application is in the queue.
QS_TIMER	A WM_TIMER message is in the queue.

dwFlags

Specifies the wait type. This parameter can be any combination of the following values:

Value	Meaning
0	The function returns when any one of the objects is signaled. The return value indicates the object whose state caused the function to return.
MWMO_WAITALL	The function returns when all objects in the pHandles array are signaled at the same time.
MWMO_ALERTABLE	The function also returns if an APC has been queued to the thread with QueueUserAPC.

Return Values

If the function succeeds, the return value indicates the event that caused the function to return. The successful return value is one of the following:

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

Remarks

The MsgWaitForMultipleObjectsEx function determines whether the conditions specified by dwWakeMask and dwFlags have been met. If the conditions have not been met, the calling thread enters an efficient wait state. The thread uses very little processor time while waiting for one of the conditions to be met or for the time-out interval to elapse.

Before returning, a wait function modifies the state of some types of synchronization objects. Modification occurs only for the object or objects whose signaled state caused the function to return. For example, the system decreases the count of a semaphore object by one.

The MsgWaitForMultipleObjectsEx function can specify handles of any of the following object types in the pHandles array:

In some circumstances, you can specify a handle of a file, named pipe, or communications device as a synchronization object in lpHandles. However, their use for this purpose is discouraged.

See Also

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

See also:

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