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MsgWaitForMultipleObjectsEx info  Overview  Group

The MsgWaitForMultipleObjectsEx function returns when one of the following occurs:

Note that 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. This is because functions such as PeekMessage, GetMessage, WaitMessage, MsgWaitForMultipleObjects, and MsgWaitForMultipleObjectsEx 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. The existing unread input 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
Points 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.

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_ALLINPUT

Any message 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.

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

Input of the type specified in the dwWakeMask parameter is available in the thread's input queue.

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.

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

Object

Description

Change notification

The FindFirstChangeNotification function returns the handle. The state of a change notification object is set to signaled when a specified change occurs within a specified directory or directory tree.

Console input

The CreateFile function returns the handle when the CONIN$ value is specified, or the GetStdHandle function returns the handle. The state of the object is set to signaled when there is unread input in the console's input buffer and nonsignaled when the input buffer is empty.

Event

The CreateEvent or OpenEvent function returns the handle. The state of an event object is set explicitly to signaled by the SetEvent or PulseEvent function. The state of a manual-reset event object must be reset explicitly to nonsignaled by the ResetEvent function. For an auto-reset event object, the wait function resets the object state to nonsignaled before returning. Event objects are also used in overlapped operations, in which the state is set by the system.

Mutex

The CreateMutex or OpenMutex function returns the handle. The state of a mutex object is signaled when it is not owned by any thread. The wait function requests ownership of the mutex for the calling thread, changing the mutex state to nonsignaled when ownership is granted.

Process

The CreateProcess or OpenProcess function returns the handle. The state of a process object is set to signaled when the process terminates.

Semaphore

The CreateSemaphore or OpenSemaphore function returns the handle. A semaphore object maintains a count between zero and the maximum count specified during its creation. Its state is set to signaled when its count is greater than zero and nonsignaled when its count is zero. If the current state of the semaphore is signaled, the wait function decreases the count by one.

Thread

The CreateProcess, CreateThread, or CreateRemoteThread function returns the handle. The state of a thread object is set to signaled when the thread terminates.

Timer

The CreateWaitableTimer or OpenWaitableTimer function returns the handle. Activate the timer by calling the SetWaitableTimer function. The state of an active timer is set to signaled when it reaches its due time. You can deactivate the timer by calling the CancelWaitableTimer function.

In some circumstances, you can specify a handle of a file, named pipe, or communications device as a synchronization object in lpHandles. However, their use for this purpose is discouraged.

See Also

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

See also:


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