This function returns when either one or all of the specified objects are in the signaled state, an I/O completion routine or asynchronous procedure call (APC) is queued to the thread, or the time-out interval elapses. This function does not return if there is unread input of the specified type in the queue. It returns only when new input arrives.
At a Glance
| Header file: | Winuser.h |
| Windows CE versions: | 2.0 and later |
Syntax
DWORD MsgWaitForMultipleObjectsEx(DWORD nCount
LPHANDLE pHandles DWORD dwMilliseconds, DWORD dwWakeMask, DWORD dwFlags);
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.
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 | Description |
| 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_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_LBUTTONDOWN, and so on) is in the queue. |
| QS_MOUSEBUTTON | A mouse-button message (WM_LBUTTONUP, WM_LBUTTONDOWN, 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. It can be any combination of the following values:
| Value | Description |
| 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_INPUTAVAILABLE | 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:
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 and GetMessage 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.
0xFFFFFFFF indicates failure. 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 copies the handle table, adds to it the message queue event, and calls WaitForMultipleObjects.
The MsgWaitForMultipleObjectsEx function can specify handles of any of the following object types in the pHandles array:
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.