Invoking function after trying to join a non-terminating thread

Question

I know that the join method blocks the current thread and waits until the task is done. So how is it possible that I can do something like this:

void task()
{
   while(true)
   {
       //do stuff
   }
}

int main()
{
   std::thread t1(task);
   t1.join();
   std::cout << "HELLO" << std::endl;
}

and still see "HELLO" after executing this code. Why does this work?

Basically answered in the question and answers here: https://stackoverflow.com/questions/3592557/optimizing-away-a-while1-in-c0x — NathanOliver, Jun 15 '17 at 18:17
Which compiler are you using? I tried your code and I have an infinite loop using Clang. — Csq, Jun 15 '17 at 18:18

gsamaras · Accepted Answer · 2017-06-15T18:23:39.040

0

This code should produce an infinite loop.

I cannot reproduce, either on GCC or in Ideone:

However, if you compile with optimization flags on, then the while loop that does nothing may be taken away by the compiler, which explains the behavior. Read more in Optimizing away a "while(1);" in C++0x, provided by Nathan Oliver.

edited Jun 15 '17 at 18:23

answered Jun 15 '17 at 18:19

gsamaras

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So does it mean that in proper circumstances it should stuck inside while loop, right? – U. Iee Jun 15 '17 at 18:22
Yes @U.Iee, it should produce an infinite loop. – gsamaras Jun 15 '17 at 18:22
Ok. I got it. But does it mean that if I want to work with threads I should just invoke join() methods inside main and let's say do nothing else? – U. Iee Jun 15 '17 at 18:27
@U.Iee when you need the threads to terminate, you can call `join()` in `main()`. – gsamaras Jun 15 '17 at 18:28

Invoking function after trying to join a non-terminating thread

1 Answers1