MsgWaitForMultipleObjectsEx with MWMO_ALERTABLE

MsgWaitForMultipleObjectsEx.cpp

// MsgWaitForMultipleObjectsEx.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <Windows.h>

VOID CALLBACK APCProc(ULONG_PTR dwParam) {
	printf("Worker thread in APCProc\n");
};

DWORD WINAPI WorkerThreadProc(LPVOID ev) {
	printf("Worker thread entry\n");
	DWORD ret = ::MsgWaitForMultipleObjectsEx(1, (HANDLE*)ev, 10000, 0, MWMO_ALERTABLE);
	switch (ret)
	{
		case WAIT_OBJECT_0:
			printf("Wait object signalled");
			break;
		case WAIT_IO_COMPLETION:
			printf("APC received in alertable wait state");
			break;
		case WAIT_TIMEOUT:
			printf("Wait timeout");
			break;
		default:
			break;
	}
	printf(" - Worker thread waiting ended\n");
	return 1;
}

int _tmain(int argc, _TCHAR* argv[])
{
	printf("Main thread entry\n");
	
	HANDLE ev = ::CreateEvent(NULL, TRUE, FALSE, NULL);
	HANDLE th = ::CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE)WorkerThreadProc, &ev, 0, NULL);

	// wait for the worker thread to go into alertable wait state
	::Sleep(3000);

	// alert waiting thread
	printf("Main thread queues APC\n");
	DWORD ii = ::QueueUserAPC(APCProc, th, 0);


	printf("Main thread joins worker thread\n");
	::WaitForSingleObject(th, INFINITE);

	::CloseHandle(ev);
	::CloseHandle(th);

	printf("Main thread exits\n");
	return 0;
}

/*

When worker thread is in alertable wait state (dwFlags == MWMO_ALERTABLE) the sequecne is as follows:

Main thread entry
Worker thread entry
Main thread queues APC
Main thread joins worker thread
Worker thread in APCProc
APC received in alertable wait state - Worker thread waiting ended
Main thread exits


When worker thread is in non alertable wait state (dwFlags == 0) the sequecne is as follows:

Main thread entry
Worker thread entry
Main thread queues APC -- note this is ignored as "the thread is not directed to call the APC function unless it is in an alertable state"!
Main thread joins worker thread
Wait timeout - Worker thread waiting ended
Main thread exits
*/