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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:

> but this is all about *invalid* threads, which obviously can't be
> joinable. i'm really not sure what you're trying to say.

Uhm, people try use pthread_kill to probe for thread termination.
Termintation of a non-detached thread doesn't make a thread
non-joinable, so from a temporal memory safety perspective, that's
totally fine.  Except that POSIX requires implementations to hide this
information from callers.

Maybe we are talking past each other, though.

Let's look at what musl does:

int pthread_kill(pthread_t t, int sig)
{
        int r;
        LOCK(t->killlock);
        r = t->tid ? -__syscall(SYS_tkill, t->tid, sig)
                : (sig+0U >= _NSIG ? EINVAL : 0);
        UNLOCK(t->killlock);
        return r;
}

The 0 could be ESRCH to support probing for termination.