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 |
); |
Windows NT: The handles must have SYNCHRONIZE access.
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. |
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. |
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 |
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 |
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.
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.
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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