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    <p>The thread id is definitely written before <code>pthread_create</code> returns. If you think about it, it would be impossible for <code>pthread_create</code> to work any other way. It could not delegate writing the thread id to the new thread, because the <code>pthread_t</code> variable might be out of scope by the time the new thread runs.</p> <p>The relevant text is:</p> <blockquote> <p>Upon successful completion, pthread_create() shall store the ID of the created thread in the location referenced by thread.</p> </blockquote> <p>(From <a href="http://pubs.opengroup.org/onlinepubs/9699919799/functions/pthread_create.html" rel="nofollow">http://pubs.opengroup.org/onlinepubs/9699919799/functions/pthread_create.html</a>) Note that it says "on successful completion" of the function, not "at an indeterminate time after successful completion".</p> <p>The more interesting question, and I'm unclear on this one, is whether <code>pthread_create</code> must have finished writing the thread id to its destination before the new thread start function begins, i.e. whether the new thread can immediately see its own thread id, e.g. if it's to be stored in a global variable. I suspect the answer is no.</p> <p><strong>Edit:</strong> Upon rereading your question, it seems like you might really have been asking about this latter, more interesting question. In any case, there's no reason for the new thread's start function to use the thread-id written out by <code>pthread_create</code>. Your new thread can (and should) just use <code>pthread_self</code> to get its own thread id.</p>
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    1. COIsn't there pthread_self() to see a thread's own ID? I think the problem lies somewhere else.
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    2. CORace conditions are only possible between different threads, not within a single thread. So the question only makes sense, I believe, if OP is asking about whether the thread id will have been written in time for the new thread to see it. The problem is easily solved by having the new thread just use `pthread_self` to get its own thread id.
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    3. COYes, race condition is possible only on different threads or processes. However, it's usually solved by locking mutexes and not tracking down the thread's ID. But hey, we don't see the codes where race conditions occur, I think I'd better leave it for the time being.
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