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boost 1.47, threads an timed_join()

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  boost 1.47, threads an timed_join() Torsten Mueller <dev-null@shared-files.de> - 2011-09-05 17:10 +0200

#9759 — boost 1.47, threads an timed_join()

I have a question related to the timed_join() method in the boost::thread
class. I had a program like this:

    #include <iostream>
    #include <boost/thread.hpp>

    using namespace std;

    class ThreadClass
    {
        public:
        void operator () ()
        {
            cout << "hello" << endl;
            sleep(5);
    	}
    };

    int main (int argc, char* argv[])
    {
        ThreadClass c;
        boost::thread th(c);

        if (th.timed_join(boost::posix_time::seconds(10)))
            cout << "ok" << endl;
        else
            cout << "timeout" << endl;

        return 0;
    }

On my Arch Linux (gcc) this runs as expected. The timed_join() waits
until the thread terminates or the timeout is reached. I can provocate
both use cases depending on the timespan in the sleep call.

On Windows (MSVC) this doesn't work anymore, I think since boost 1.47.
It worked without any problem for years using older boost versions but
now it is like follows: After the thread is created it's run method (the
operator ()) is not called immediately but somehow later. This gives
timed_join() the opportunity to be called on a thread which still seems
not truely to be running. So timed_join() returns immediately false,
which is wrong! Then, after timed_join(), the operator () is still
called. This is unusable.

I tried to use a unique lock on a mutex to synchronize the calling and
the called thread. This reorders the function calling sequence: the
operator () is called before timed_join() is executed. So timed_join()
finds truely a running thread but returns again false. Why?

The join() method of the thread class behaves different: join() does
truely wait, even if the thread needs a lot of time to start. I think
this difference is not intended. So is this a bug in boost 1.47?

T.M.

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