MsgWaitForMultipleObjectsEx function

Waits until 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. The array of objects can include input event objects, which you specify using the dwWakeMask parameter.

Syntax

DWORD WINAPI MsgWaitForMultipleObjectsEx(
  _In_       DWORD  nCount,
  _In_ const HANDLE *pHandles,
  _In_       DWORD  dwMilliseconds,
  _In_       DWORD  dwWakeMask,
  _In_       DWORD  dwFlags
);

Parameters

nCount [in]

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]

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 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.

The handles must have the SYNCHRONIZE access right. For more information, see Standard Access Rights.

dwMilliseconds [in]

The time-out interval, in milliseconds. If a nonzero value is specified, the function waits until the specified objects are signaled, an I/O completion routine or APC is queued, or the interval elapses. If dwMilliseconds is zero, the function does not enter a wait state if the criteria is not met; it always returns immediately. If dwMilliseconds is INFINITE, the function will return only when the specified objects are signaled or an I/O completion routine or APC is queued.

dwWakeMask [in]

The input types for which an input event object handle will be added to the array of object handles. This parameter can be one or more of the following values.

Value	Meaning
QS_ALLEVENTS 0x04BF	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 0x04FF	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 0x0100	A posted message is in the queue. This value is cleared when you call GetMessage or PeekMessage without filtering messages.
QS_HOTKEY 0x0080	A WM_HOTKEY message is in the queue.
QS_INPUT 0x407	An input message is in the queue. This value is a combination of QS_MOUSE, QS_KEY, and QS_RAWINPUT.
QS_KEY 0x0001	A WM_KEYUP, WM_KEYDOWN, WM_SYSKEYUP, or WM_SYSKEYDOWN message is in the queue.
QS_MOUSE 0x0006	A WM_MOUSEMOVE message or mouse-button message (WM_LBUTTONUP, WM_RBUTTONDOWN, and so on). This value is a combination of QS_MOUSEMOVE and QS_MOUSEBUTTON.
QS_MOUSEBUTTON 0x0004	A mouse-button message (WM_LBUTTONUP, WM_RBUTTONDOWN, and so on).
QS_MOUSEMOVE 0x0002	A WM_MOUSEMOVE message is in the queue.
QS_PAINT 0x0020	A WM_PAINT message is in the queue.
QS_POSTMESSAGE 0x0008	A posted message is in the queue. This value is cleared when you call GetMessage or PeekMessage, whether or not you are filtering messages.
QS_RAWINPUT 0x0400	A raw input message is in the queue. For more information, see Raw Input.
QS_SENDMESSAGE 0x0040	A message sent by another thread or application is in the queue.
QS_TIMER 0x0010	A WM_TIMER message is in the queue.

 

dwFlags [in]

The wait type. This parameter can be one or more 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_ALERTABLE 0x0002	The function also returns if an APC has been queued to the thread with QueueUserAPC while the thread is in the waiting state.
MWMO_INPUTAVAILABLE 0x0004	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.
MWMO_WAITALL 0x0001	The function returns when all objects in the pHandles array are signaled and an input event has been received, all at the same time.

 

Return value

If the function succeeds, the return value indicates the event that caused the function to return. It can be one of the following values. (Note that WAIT_OBJECT_0 is defined as 0 and WAIT_ABANDONED_0 is defined as 0x00000080L.)

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 until the conditions of the wait criteria have been met or the time-out interval elapses.

When dwFlags is zero, this function checks the handles in the array in order starting with index 0, until one of the objects is signaled. If multiple objects become signaled, the function returns the index of the first handle in the array whose object was signaled.

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.

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. For more information, see the documentation for the individual synchronization objects.

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

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

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

See also

Synchronization Functions

Wait Functions