C++ kill method without constantly checking flags

Question

I have several work functions, that call accessory functions that might have something bad happen. I want to be able to stop the work functions if an accessory function determines something bad happened, without putting numerous flag checks in the work functions. For example,

struct Worker {
    bool badhappened = false;
    Worker() {
        std::thread([&]() {
            while ( not badhappened );
            // kill the work
        }).detach();
    }
    int WorkComponent {
        if ( badhappening() )
            badhappened = true;
        return someint;
    }
    void DoWork {
        // WorkComponents called several times
    }
}

But I don't know what to call at kill the work. It's not a problem for DoWork to happen in a separate thread, but there doesn't appear to be an equivalent pthread_kill in C++'s threads. Is there a solution that doesn't involve putting several if(badhappened) return; calls into DoWork?

You could use Boost threads instead, as they have termination points that can be checked (which is not much different than checking a variable I admit). However, forcibly killing a thread might be bad, especially if the thread has allocated resources. — Some programmer dude, Oct 17 '12 at 13:55
@JoachimPileborg `pthread_kill`, to my knowledge, can send a similar termination signal that `kill` does. I imagine there's a similar mechanic in `std::thread`, just don't know what it is. @MartinJames That could work actually, it shouldn't happen often enough to be a noticeable performance hit. Good idea, thanks! — Mike Barriault, Oct 17 '12 at 14:03
Unfortunately there are no such features in `std::thread`, but I hope it comes in the next C++ standard (whenever that comes). However, you can use the [`std::thread::native_handle`](http://en.cppreference.com/w/cpp/thread/thread/native_handle) function to get the native pthread (hopefully) handle and then call `pthread_kill`. — Some programmer dude, Oct 17 '12 at 14:08

score 6 · Answer 1 · edited May 23 '17 at 10:24

Long story short:

There is no safe way to stop a non-cooperative thread.

Yes, there are tools to forcibly shut down a thread but you are asking for trouble. The only safe way is to agree on a termination policy. This boils down to checking a flag sufficiently frequently as you write.

C++ kill method without constantly checking flags

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