MsgWaitForMultipleObjectsEx

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Windows Embedded CE 6.0 R3

4/8/2010

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.

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_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 Value

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_Zero 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_Zero 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:

• Event
• Mutex
• Critical section
• Semaphore
• Process
• Thread

The QS_POSTMESSAGE flag is cleared when you call GetMessage or PeekMessage, whether or not you are filtering messages.

Requirements

See Also

Reference

Message Queue Functions
PeekMessage
GetMessage
WM_KEYUP
WM_KEYDOWN
WM_SYSKEYUP
WM_SYSKEYDOWN
WM_MOUSEMOVE
WM_LBUTTONUP
WM_LBUTTONDOWN
WM_PAINT
WM_TIMER

Other Resources

WaitForMultipleObjects