Re: [PATCH] pthread_kill.3: Update to match POSIX.

[Florian Weimer <fw@deneb.enyo.de>]

> any comment from either of the maintainers?
>
> i think what we currently have on this page is factually incorrect,
> and this patch better matches reality.

One more data point:

As of glibc 2.34, pthread_kill in glibc cannot fail with ESRCH anymore
(unless the kernel thread is terminated by a direct system call).  And
the race that the signal could be sent to the wrong thread is gone.

> On Tue, Nov 12, 2019 at 10:10 PM Florian Weimer <fw@deneb.enyo.de> wrote:
>>
>> * enh:
>>
>> > On Tue, Nov 12, 2019 at 9:51 PM Florian Weimer <fw@deneb.enyo.de> wrote:
>> >>
>> >> * 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.
>> >
>> > ah, you're trying to say "signal 0 is potentially usable for a
>> > joinable thread that's waiting to be joined"? that's true, but i'm not
>> > sure how that's relevant to this patch. that wouldn't be an "invalid
>> > thread ID" until it's joined.
>>
>> Correct.  That's POSIX's argument why ESRCH wouldn't be valid to
>> return here.  It's still a forceful loss of information, and
>> particularly annoying since POSIX doesn't specify pthread_tryjoin.
>>
>> But I'm glad we've brought our discussion to a conclusion. 8-)