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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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Date:   Tue, 12 Nov 2019 22:38:10 +0100
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* enh:

> POSIX removed ESRCH years ago.
>
> In resolving http://austingroupbugs.net/view.php?id=1214 it was made
> clear that callers can't rely on using signal 0 to test for the
> continued existence of a thread. Update the man page to make it clearer
> that this doesn't generally work (even if it sometimes seems to).
>
> See also the long explanation of why this is the case (and how to fix
> your code) here:
>
> https://android.googlesource.com/platform/bionic/+/master/docs/status.md#invalid-handling-targetsdkversion-o

Well, if you fix the thread exit race (like musl did, and glibc should
as well, see bug 12889), you could get a reliable ESRCH as a side
effect.  Pity that POSIX doesn't allow that.

I think this might be a case where common (but not unavoidable)
implementation problems get in the way of a better standard.  Usually,
it's the other way round.