Re: [Boost-Users] boost::thread and detaching

From: William E. Kempf (wekempf_at_[hidden])
Date: 2003-05-21 12:24:22

Aatu Koskensilta said:
> Hello.
>
> I have a very simple server, in which there is a loop that looks like
>
> while( (c_sock = accept(...)) != -1)
> {
>   try
>   {
>    boost::thread thr( boost::bind(&ServerClass::client_connection, this,
>                                   c_sock));
>   }catch ( const std::exception & e)
>   {
>    std::cout << "Exception " << e << std::endl;
>    close(c_sock);
>   }
> }
>
> Now, it used to look more like
>
> while( (c_sock = accept(...)) != -1)
> {
>      pthread_t thr;
>      pthread_attr_t attrs;
>      pthread_attr_init(&attrs);
>      pthread_attr_setdetachstate(&attrs, PTHREAD_CREATE_DETACHED);
> thr_data * data = new thr_data(this, c_sock);
>      pthread_create(&thr, &attrs, thread_proxy_function, thr_data);
> }
>
> (Actually, the pthread specific stuff and thread parameter wrapping and
> all that that was done with wrappers written by me. Also, there was
> proper error checking and all.)
>
> Now, the older version worked without any problems. However, the newer
> version using boost::thread ceased to work after approximately 256
> threads had been created *all of which had exited*, pthread_create
> reporting an error Memory allocation failed which was reported as a
> resource allocation error by boost::thread.
>
> It seems that this problem was caused by the fact that the thread
> function usually got to execute and finish *before* the temporary thread
>  object was destroyed (boost::thread destructor calls pthread_detach).
> Apparently LinuxThreads didn't consider it prudent to release the
> resources allocated to the thread upon call of pthread_detach if the
> thread had exited but no one had joined it yet.
>
> Is my analysis credible?

Sounds credible... but I didn't know the POSIX standard behaved in this
manner (i.e. detaching a thread that had already ended would leak
resources instead of behaving like a join in this case).  I'll have to
research both the standard and my own code here.

> Am I doing something completely idiotic here?

No.

> I
>  managed to get my server code functioning by poking at the
> boost::thread  code and making it create threads detached by default,
> but that's hardly  a very elegant solution.

Agreed.

> I'm testing this code in a RedHat 9 Linux box.

Do you have a short test case for this?

-- 
William E. Kempf