MsgWaitForMultipleObjectsEx

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  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 array
  CONST HANDLE pHandles, // object-handle array
  DWORD dwMilliseconds,  // time-out interval
  DWORD dwWakeMask,      // input-event type
  DWORD dwFlags          // wait options
);

Parameters

nCount

[in] 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

[in] 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. It may not contain the multiple copies of the same handle.

If one of these handles is closed while the wait is still pending, the function's behavior is undefined.

Windows NT/2000: The handles must have SYNCHRONIZE access. For more information, see Standard Access Rights.

dwMilliseconds

[in] 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

[in] 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. This value is a combination of QS_INPUT, QS_POSTMESSAGE, QS_TIMER, QS_PAINT, and QS_HOTKEY.
QS_ALLINPUT	Any message is in the queue. This value is a combination of QS_INPUT, QS_POSTMESSAGE, QS_TIMER, QS_PAINT, QS_HOTKEY, and QS_SENDMESSAGE.
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. This value is a combination of QS_MOUSE and QS_KEY.
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. This value is a combination of QS_MOUSEMOVE and QS_MOUSEBUTTON.
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

[in] 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 and an input event has been received, all 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 2000: 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:

If the function fails, the return value is -1. 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 the wait state. It uses no processor time while waiting for one of the conditions to be met or for the time-out interval to elapse.

The 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:

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

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.

Requirements

  Windows NT/2000: Requires Windows NT 4.0 or later.
  Windows 95/98: Requires Windows 98.
  Header: Declared in Winuser.h; include Windows.h.
  Library: Use User32.lib.

See Also

Synchronization Overview, Synchronization Functions