QueueUserAPC
[New
- Windows NT]
The QueueUserAPC
function adds a user-mode asynchronous procedure call (APC) object to the APC
queue of the specified thread.
DWORD QueueUserAPC(
|
PAPCFUNC pfnAPC, |
// pointer
to APC function |
|
HANDLE hThread, |
// handle
to the thread |
|
DWORD dwData |
// argument
for the APC function |
|
); |
|
Parameters
pfnAPC
Points to the
application-supplied APC function to be called when the specified thread
performs an alertable wait operation.
hThread
Specifies the
handle to the thread. The handle must have THREAD_SET_CONTEXT access. For more
information, see Thread Objects.
dwData
Specifies a
single DWORD argument that is passed to the APC function pointed to by the pfnAPC
parameter.
Return Values
If the
function succeeds, the return value is TRUE.
If the
function fails, the return value is FALSE. There are no error values defined
for this function that can be retrieved by calling GetLastError.
Remarks
The APC
support provided in the operating system allows an application to queue an APC
object to a thread. Each thread has its own APC queue. The queuing of an APC is
a request for the thread to call the APC function. The operating system issues
a software interrupt to direct the thread to call the APC function.
When a
user-mode APC is queued, the thread is not directed to call the APC function
unless it is in an alertable state. A thread enters an alertable state by using
SleepEx, SignalObjectAndWait, WaitForSingleObjectEx, WaitForMultipleObjectsEx, or MsgWaitForMultipleObjectsEx to perform an alertable
wait operation. After the thread is in an alertable state, the thread handles
all pending APCs in first in, first out (FIFO) order, and the wait operation
returns WAIT_IO_COMPLETION.
If an
application queues an APC before the thread begins running, the thread begins
by calling the APC function. Once the thread calls an APC function, it calls
the APC functions for all APCs in its APC queue.
When the
thread is terminated using the ExitThread or TerminateThread function, the APCs in its
APC queue are lost. The APC functions are not called.
Note that the
ReadFileEx and WriteFileEx functions are
implemented using an APC as the completion notification callback mechanism.
See Also