MFC: How to use MsgWaitForMultipleObjects() from the main thread to wait for multiple threads to complete that use SendMessage()? - winapi

Question

I have a main thread that fires off several other threads to complete various items of work based on what the user choose from the main UI. Normally I'd use WaitForMultipleObjects() with bWaitAll set to TRUE. However, in this case those other threads will log output to another window that uses a mutex to ensure the threads only output one at a time. Part of that process uses SendMessage() to send get the text size and send the text to the windows which will hang if using WaitForMultipleObjects() since it's running from the main UI thread. So I moved over to use MsgWaitForMultipleObjects with QS_SENDMESSAGE flag, only it's problem is the logic for bWaitAll which states it will only return if all objects are signaled AND an input event occurred (instead of returning when all objects are signaled OR an input event occurred). Had the logic been OR this should have worked:
DWORD waitres=WAIT_FAILED;
while (1)
{
MSG msg;
while (::PeekMessage(&msg, NULL, 0, 0, PM_NOREMOVE)) {
// mfc message pump
if (!theApp.PumpMessage()) {
// program end request
// TO DO
}
}
// MFC idel processing
LONG lidlecount = 0;
while (theApp.OnIdle(lidlecount++));
// our wait
waitres = ::MsgWaitForMultipleObjects(threadcount, threadhandles, TRUE, INFINITE, QS_SENDMESSAGE);
// check if ended due to message
if (waitres!=WAIT_OBJECT_0+threadcount) {
// no, exit loop
break;
}
}
Rather than fire off a thread that then fires off the other threads I wondered what is the correct way to handle this from the main thread? I thought about using bWaitAll FALSE then using WaitForMultipleObjects() with bWaitAll set to TRUE and the dwMilliseconds set to 0 (or 1) and checking the result to see if completed. If not, it would need to loop back to the top of the loop and then to MsgWaitForMultipleObjects() which when using bWaitAll FALSE could return right away if one of the many threads completed (say 1 thread of 10 completed, I could check as mentioned above if all completed, but when going back with bWaitAll FALSE it will just return and not wait).
So what is the proper way to handle waiting for multiple threads (that use SendMessage()) to complete in the main thread of an MFC application?
Thanks.

Answer 1

So what is the proper way to handle waiting for multiple threads to
complete
need create some structure, with reference count and pass pointer to this structure to every thread. here also probably exist sense have some common task data. and HWND of some window in main(GUI) thread. when worked thread exit - it release reference on object. when last thread exit - delete object and post some message to window, from main thread.
so we not need store thread handles (can just close it) and wait om multiple handles. instead we got some window message when all thread finish task
example of code
struct Task
{
HWND _hwnd;
LONG _dwRefCount = 1;
// some common task data probably ..
Task(HWND hwnd) : _hwnd(hwnd) {}
~Task() {
PostMessageW(_hwnd, WM_USER, 0, 0);// WM_USER as demo only
}
void AddRef(){
InterlockedIncrementNoFence(&_dwRefCount);
}
void Release(){
if (!InterlockedDecrement(&_dwRefCount)) delete this;
}
};
ULONG CALLBACK WorkThread(void* pTask)
{
WCHAR sz[16];
swprintf_s(sz, _countof(sz), L"%x", GetCurrentThreadId());
MessageBoxW(0, L"working...", sz, MB_ICONINFORMATION|MB_OK);
reinterpret_cast<Task*>(pTask)->Release();
return 0;
}
void StartTask(HWND hwnd, ULONG n)
{
if (Task* pTask = new Task(hwnd))
{
do
{
pTask->AddRef();
if (HANDLE hThread = CreateThread(0, 0, WorkThread, pTask, 0, 0))
{
CloseHandle(hThread);
}
else
{
pTask->Release();
}
} while (--n);
pTask->Release();
}
}