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    <p><code>libgomp</code> implements thread pools. Once created, a thread in the pool remains idle until it is signalled to become member of a thread team. After the team finishes its work, the thread goes into an idle loop until it is signalled again. The pool grows on demand but never shrinks. Threads are only signalled to exit at program finish.</p> <p>You can read the <code>libgomp</code> code that implements thread pools and teams in the 4.7.x branch <a href="http://gcc.gnu.org/svn/gcc/branches/gcc-4_7-branch/libgomp/team.c" rel="nofollow">here</a>.</p> <p>Pool threads are terminated like this: <code>libgomp</code> registers a destructor by the name of <code>team_destructor()</code>. It is called whenever the <code>main()</code> function returns, <code>exit(3)</code> gets called or the <code>libgomp</code> library is unloaded by a call to <code>dlclose(3)</code> (if previously loaded with <code>dlopen(3)</code>). The destructor deletes one <code>pthreads</code> key by the name of <code>gomp_thread_destructor</code>, which has an associated destructor function <code>gomp_free_thread()</code> triggered by the deletion. <code>gomp_free_thread()</code> makes all threads in the pool execute <code>gomp_free_pool_helper()</code> as their next task. <code>gomp_free_pool_helper()</code> calls <code>pthread_exit(3)</code> and thus all threads in the pool cease to exist.</p> <p>Here is the same process in a nice ASCII picture:</p> <pre><code>main() returns, exit() called or library unloaded | | team_destructor() deletes gomp_thread_destructor | | gomp_free_thread() called by pthreads on gomp_thread_destructor deletion | +-------------------------+---------------------------+ | | | gomp_free_pool_helper() gomp_free_pool_helper() ... gomp_free_pool_helper() installed as next task installed as next task installed as next task | | | | | | pthread_exit(NULL) pthread_exit(NULL) ... pthread_exit(NULL) </code></pre> <p>Note that this only happens once at the end of the program execution and not at the end of each <code>parallel</code> region.</p>
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    1. COHi Hristo, Thank you for the answer. As far as I understood, when the program exits i.e. the thread gets the signal, it doesn't call pthread_exit(). It seems like I need to change the code for this file (team.c) to do this. Is that right? If it is, is there any simple way to do this?
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    2. COThreads run the loop in the second half of `gomp_thread_start()` as long as they have a function to execute after the docking barrier, otherwise they exit the loop and simply return. There is one case when threads call `pthread_exit` and that is the case when `libgomp` was loaded at runtime with `dlopen(3)`. There is one key `gomp_thread_destructor` with an associated destructor `gomp_free_thread()` and a file destructor by the name of `team_destructor()` is registered. When you `dlclose(3)` the library, the file destructor get called and it makes all team threads call `pthread_exit`.
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    3. COSorry, my mistake - functions with `__attribute__((destructor))` are also called after `main()` returns. It means that pool threads would surely reach the point where they call `pthread_exit` but not before the `main` function has returned. Unfortunately the `libgomp` API is not available to the user and you cannot invoke the pool destructor before the end of `main()`.
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