CODEWITHSUNDEEP
c++multithreadingwinapi
user1853098
user1853098

Reputation: 119

Windows Api Multi-threading Messages

I'm just curious as to to how to implement multi-threading without using a Windows API WaitFor* function that stops the program until the thread has returned. What's the point of using threads if they stop the main application from being resized or moved etc.?

Is there any form of windows messaging with threading, which will allow me to call my thread function and then return, and handle the return values of the thread when it finishes running?

Upvotes: 2

Views: 715

Answers (4)

Rost
Rost

Reputation: 9089

WaitForSingleObject can be non-blocking, just pass zero timeout as second parameter:

// Check is thread has been finished
if(::WaitForSingleObject(threadHandle, 0) == WAIT_OBJECT_0)
{
   // Process results
   ...
}

You will need to periodically check this condition, e.g. on timer or after processing any message in message loop.

Or you can use MsgWaitForMultipleObjectsEx. It will unblock and return when some message/input event occured in calling thread message queue.

As other answers mentioned there is another way - using Windows asynchronously posted message to signal that thread has done its work. This way has disadvantage - the working thread must know target window or thread to post message to. This dependency complicates design and raises issues about checking thread/window lifetime. To avoid it message broadcasting (PostMessage(HWND_BROADCAST,...)) can be used, but this is overkill for your case, I don't recommend it.

Upvotes: 1

nanda
nanda

Reputation: 804

If you want your UI thread to know when a task thread has finished it's task then you could have your task thread post a (custom - WM_USER and above) message to your main window (along with thread id plus the handle). And the window proc of the main window can know that a particular task thread has finished it's task. This way the UI thread does not have to wait actively (using WaitFor*) on the thread(s) object.

Upvotes: 3

Jonathan Potter
Jonathan Potter

Reputation: 37192

You can use MsgWaitForMultipleObjectsEx to wait for the thread to finish and also process messages at the same time.

Upvotes: 2

Stephane Rolland
Stephane Rolland

Reputation: 39926

Have a look at std::thread, boost::thread, just::thread, for multithreading in general for c++.

But about Windows messaging win32 and MFC, the MSDN states explicitely that it is not multithread, it is monothread. ( Undefined behaviour is to be expected if multithreading is used)

For asynchronous message emited in other thread than the main application window thread, you should use ::PostMessage(), that will insert message events in the monothread message pump of the mono threaded window.

Upvotes: 1

Related Questions