CODEWITHSUNDEEP
winapivisual-c++multithreading
Akaanthan Ccoder
Akaanthan Ccoder

Reputation: 2179

In threads, WaitForMultipleObjects never returns if set to INFINITE

Let say I have three thread handles

HandleList[0] = hThread1;
HandleList[1] = hThread2;
HandleList[2] = hThread3;
/*All the above are of type HANDLE*/

Before closing the application, I want the thread to get its task done. So I want to make app wait till thread completes.

So I do,

WaitForMultipleObjects(3, HandleList, TRUE, INFINITE );

By this I'm able to make the thread, complete its task. But control never move to next line after the call to WaitForMultileObjects irrespective of all thread completing its task.

If I use, some seconds instead of INFINITE, it comes to next line after that many secs, irrspective of whether thread completes its task or not.

WaitForMultipleObjects(3, HandleList, TRUE, 10000 );

My problem here is, I'm can't go for seconds, as I may not be sure whether the threads will complete its task with the given time.

To list my problem in simple words, I want all my thread to finish the task, before I close my app. How can I achieve it using WaitForMultipleObjects API?

EDIT: As per MSDN..

dwMilliseconds [in] Time-out interval, in milliseconds.

Upvotes: 1

Views: 3809

Answers (3)

Lasse V. Karlsen
Lasse V. Karlsen

Reputation: 391276

The simple answer is that you cannot achieve this with WaitForMultipleObjects.

The problem here is that the fault is not with this function, it's doing exactly what it is supposed to do, it waits for the threads to finish.

The problem here is that one or more of the threads never finish.

And that is the problem you need to solve. Why isn't the threads finishing?

Are they deadlocked? Are they running in a loop they aren't breaking out of?

Upvotes: 1

Sergey Podobry
Sergey Podobry

Reputation: 7189

You should signal all your threads to finish the job with SetEvent or by anything else. And be sure not to wait for itself.

Upvotes: 3

anon
anon

Reputation:

In your code you say:

WaitForMultipleObjects(3, HandleList, TRUE, INFINITE );

which will wait until all three threads have finished. Is this what you want? If you want to wait until any one of them is finished, you want:

WaitForMultipleObjects(3, HandleList, FALSE, INFINITE );

If the first version never returns, then it is because at least one of the threads never terminates. You might also want to look at the provisos on threads that create windows in the API docs at http://msdn.microsoft.com/en-us/library/ms687025%28VS.85%29.aspx.

Upvotes: 2

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