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PO
 

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  1. PO
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    <p>Here is an example taken from the <a href="http://www.gnu.org/s/pth/" rel="nofollow">GnuPth</a>(<code>pth_lib.c</code>) user-level threading library, which shows the implementation of the <code>exit</code> and <code>join</code> functions, respectively. I <strong>simplified</strong> the code to highlight the return value handling.</p> <pre><code>void pth_exit(void *value) { pth_debug2("pth_exit: marking thread \"%s\" as dead", pth_current-&gt;name); /* the main thread is special, because its termination would terminate the whole process, so we have to delay its termination until it is really the last thread */ /* execute cleanups */ /* * Now mark the current thread as dead, explicitly switch into the * scheduler and let it reap the current thread structure; we can't * free it here, or we'd be running on a stack which malloc() regards * as free memory, which would be a somewhat perilous situation. */ pth_current-&gt;join_arg = value; pth_current-&gt;state = PTH_STATE_DEAD; pth_debug2("pth_exit: switching from thread \"%s\" to scheduler", pth_current-&gt;name); //return (for ever) to the scheduler } </code></pre> <p>and the corresponding <code>pth_join</code>:</p> <pre><code>/* waits for the termination of the specified thread */ int pth_join(pth_t tid, void **value) { //Validate thread situation. //wait until thread death //save returned value for the caller if (value != NULL) *value = tid-&gt;join_arg; //remove thread from the thread queue //free its memory space return TRUE; } </code></pre>
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    1. POImplementing join function in a user level thread library
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    1. USKevin
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    1. COThanks for the response. As i understand, u will not free the context associated with the thread in exit function. But, when do you actually do it? It can be done in join function, but what if the thread was never joined by any other thread. when does the freeing happen in this case?
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    2. COyes, Gnupth (not me!) frees the thread data in the `join` function. As far as I remember (correct me if I'm wrong), the POSIX interface makes mandatory the `join` operation, unless a specific thread attribute is set. So you can add a hook in `exit` to release the memory in this particular situation.
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