MsgWaitForMultipleObjectsEx

The MsgWaitForMultipleObjectsEx function returns when one of the following occurs:

Note  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, unless you use the MWMO_INPUTAVAILABLE flag. This is because functions such as PeekMessage, GetMessage, GetQueueStatus, and WaitMessage 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, unless you use the MWMO_INPUTAVAILABLE flag. If this flag is not used, the existing unread input (received prior to the last time the thread checked the queue) is ignored. 

DWORD MsgWaitForMultipleObjectsEx(
  DWORD nCount,          // number of handles in handle array
  LPHANDLE pHandles,     // pointer to an object-handle array
  DWORD dwMilliseconds,  // time-out interval in milliseconds
  DWORD dwWakeMask,      // type of input events to wait for
  DWORD dwFlags          // wait flags
);

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
Pointer 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. For more information, see Standard Access Rights.

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_ALLEVENTS An input, WM_TIMER, WM_PAINT, WM_HOTKEY, or posted message is in the queue.
QS_ALLINPUT Any message is in the queue.
QS_ALLPOSTMESSAGE A posted message (other than those listed here) 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.
MWMO_INPUTAVAILABLE Windows 98, Windows NT 5.0 and later: The function returns if input exists for the queue, even if the input has been seen (but not removed) using a call to another function, such as PeekMessage.

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:

Value Meaning
WAIT_OBJECT_0 to
(WAIT_OBJECT_0 + nCount - 1)		 If the MWMO_WAITALL flag is used, the return value indicates that the state of all specified objects is signaled. Otherwise, the return value minus WAIT_OBJECT_0 indicates the pHandles array index of the object that caused the function to return.
WAIT_OBJECT_0 + nCount New input of the type specified in the dwWakeMask parameter is available in the thread's input queue. Functions such as PeekMessage, GetMessage, GetQueueStatus, and WaitMessage mark messages in the queue as old messages. Therefore, after you call one of these functions, a subsequent call to MsgWaitForMultipleObjectsEx will not return until new input of the specified type arrives.

This value is also returned upon the occurrence of a system event that requires the thread's action, such as foreground activation. Therefore, MsgWaitForMultipleObjectsEx can return even though no appropriate input is available and even if dwWaitMask is set to 0. If this occurs, call PeekMessage or GetMessage to process the system event before trying the call to MsgWaitForMultipleObjectsEx again.

WAIT_ABANDONED_0 to
(WAIT_ABANDONED_0 + nCount - 1)		 If the MWMO_WAITALL flag is used, the return value indicates that the state of all specified objects is signaled and at least one of the objects is an abandoned mutex object. Otherwise, the return value minus WAIT_ABANDONED_0 indicates the pHandles array index of an abandoned mutex object that caused the function to return.
WAIT_IO_COMPLETION The wait was ended by a user-mode asynchronous procedure call (APC) queued to the thread.
WAIT_TIMEOUT The time-out interval elapsed, but the conditions specified by the dwFlags and dwWakeMask parameters were not met.

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. When dwFlags is zero, and multiple objects are in the signaled state, the function chooses one of the objects to satisfy the wait; the states of the objects not selected are unaffected.

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

For more information, see Synchronization Objects.

The QS_ALLPOSTMESSAGE and QS_POSTMESSAGE flags differ in when they are cleared. QS_POSTMESSAGE is cleared when you call GetMessage or PeekMessage, whether or not you are filtering messages. QS_ALLPOSTMESSAGE is cleared when you call GetMessage or PeekMessage without filtering messages (wMsgFilterMin and wMsgFilterMax are 0). This can be useful when you call PeekMessage multiple times to get messages in different ranges.

Windows CE: Windows CE does not support the QS_HOTKEY value for the dwWakeMask parameter or the MWMO_WAITALL and MWMO_ALERTABLE flags for the dwFlags parameter.

The MsgWaitForMultipleObjectsEx function copies the handle table, adds to it the message queue event, and calls WaitForMultipleObjects.

QuickInfo

  Windows NT: Requires version 4.0 or later.
  Windows: Requires Windows 98 or later.
  Windows CE: Requires version 2.0 or later.
  Header: Declared in winuser.h.
  Import Library: Use user32.lib.

See Also

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