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From:   Florian Weimer <fw@deneb.enyo.de>
To:     enh <enh@google.com>
Cc:     "Michael Kerrisk \(man-pages\)" <mtk.manpages@gmail.com>,
        linux-man@vger.kernel.org
Subject: Re: [PATCH] pthread_kill.3: Update to match POSIX.
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* enh:

> no, because the C library has two choices when a thread exits:
>
> 1. unmap the thread.
>
> 2. keep the thread around for recycling.
>
> if you choose 1 (optimizing for space, like Android), your dereference
> is illegal.

This choice is only available for threads in a detached state.  For
joinable threads, a conforming implementation cannot immediately
deallocate all data structures on thread termination.  Among other
things, it has to store the future return value of pthread_join
somewhere.