Re: What does this code print ?

From	Kaz Kylheku <864-117-4973@kylheku.com>
Newsgroups	comp.lang.c++
Subject	Re: What does this code print ?
Date	2023-10-14 02:36 +0000
Organization	A noiseless patient Spider
Message-ID	<20231013192405.57@kylheku.com> (permalink)
References	(1 earlier) <87lec95n0t.fsf@bsb.me.uk> <ugaeqo$2vefi$1@dont-email.me> <ugapal$31eim$1@dont-email.me> <20231013081459.652@kylheku.com> <ugc8bo$3cv2m$1@dont-email.me>

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On 2023-10-13, Chris M. Thomasson <chris.m.thomasson.1@gmail.com> wrote:
> Afaict, thread_local should be using the thread that is calling main in 
> this example.

If the program has not started any threads, so that there is only
the primary thread that starts at main, thread_local could be
replaced by static.

> I should create a new thread for this, but:
>
> Fwiw, actually, I am trying to understand how dtors are called wrt TLS 
> when a thread is destroyed (aka, join returns) in C++. POSIX and C11 
> makes this rather easy wrt:
>
> Notice the dtor that we can use wrt (thread local storage) TLS:
>
> https://en.cppreference.com/w/c/thread/tss_create
>
> This is basically how POSIX does it via:
>
> pthread_key_t
> _______________
> pthread_key_create
> pthread_setspecific
> pthread_getspecific
> pthread_key_delete
> _______________

The pthread_key_delete function is rarely needed. We would need it in,
say, a dynamically loaded component that is being unloaded.

Usually keys have an indefinite lifetime. The values don't, of course.

In pthread_key_create we can register a destructor function
that is used upon thread death.

This is extremely badly designed in POSIX, because that thread which is
terminated is tasked with the clean-up of the keys: the destructors
run in its context.

While it's performing the clean-up for one key, it might inadvertently
call some code which reinstalls the value for another key.

In recognition of this problem, the API is designed with a silly
iteration mechanism. If the terminating thread has reinstanted
values for any thread specific keys, those are iterated on again
and the destructors are called, up to some number of times.

What you want is to allow the thread to just exit. In that thread's
context, at most you want to do unwinding of its scoped resources.

The thread-specific keys values of a thread should persist until it
has terminated, and then be cleaned up at some later time by
*another* thread. Kind of like a garbage collection pass.

If the thread is pthread_join-ed, the one doing the joining would
be a good candidate. For detached threads, it could be done by some
internal thread, or foisted onto some existing application thread
when it happens to bump into the pthread key API.

That would prevent the need for iterations because, since another
thread is running the destructors, and not the original one,
That other thread can only set its own key values, and not those
of another thread, let alone a dead one.

Some 25 years ago I made a TLS API like that, with the cleanup
done on another thread. It worked well.

-- 
TXR Programming Language: http://nongnu.org/txr
Cygnal: Cygwin Native Application Library: http://kylheku.com/cygnal
Mastodon: @Kazinator@mstdn.ca
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Thread

What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-11 05:30 +0200
  Re: What does this code print ? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-10-11 14:03 +0100
    Re: What does this code print ? gazelle@shell.xmission.com (Kenny McCormack) - 2023-10-11 13:12 +0000
      Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-11 19:22 +0200
        Re: What does this code print ? scott@slp53.sl.home (Scott Lurndal) - 2023-10-11 17:41 +0000
          Re: What does this code print ? Bo Persson <bo@bo-persson.se> - 2023-10-11 20:24 +0200
          Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-13 05:24 +0200
            Re: What does this code print ? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-10-13 17:53 +0100
              Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-14 15:50 +0200
        Re: What does this code print ? Richard Damon <richard@damon-family.org> - 2023-10-13 12:12 -0400
          Re: What does this code print ? scott@slp53.sl.home (Scott Lurndal) - 2023-10-13 17:27 +0000
          Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-14 15:52 +0200
            Re: What does this code print ? Richard Damon <richard@damon-family.org> - 2023-10-14 11:26 -0400
              Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-15 09:08 +0200
                Re: What does this code print ? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2023-10-15 12:55 -0700
                Re: What does this code print ? Richard Damon <news.x.richarddamon@xoxy.net> - 2023-10-15 22:19 -0400
                Re: What does this code print ? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2023-10-18 20:58 -0700
    Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-11 19:21 +0200
    Re: What does this code print ? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2023-10-11 12:41 -0700
      Re: What does this code print ? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2023-10-11 12:43 -0700
      Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-13 05:25 +0200
    Re: What does this code print ? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2023-10-12 20:50 -0700
      Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-13 08:50 +0200
        Re: What does this code print ? Richard Damon <richard@damon-family.org> - 2023-10-13 12:15 -0400
          Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-14 15:53 +0200
            Re: What does this code print ? Richard Damon <richard@damon-family.org> - 2023-10-14 11:26 -0400
              Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-15 09:00 +0200
                Re: What does this code print ? Richard Damon <richard@damon-family.org> - 2023-10-15 13:15 -0400
                Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-17 07:47 +0200
                Re: What does this code print ? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2023-10-17 11:34 -0700
        Re: What does this code print ? Kaz Kylheku <864-117-4973@kylheku.com> - 2023-10-13 16:34 +0000
          Re: What does this code print ? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2023-10-13 13:12 -0700
            Re: What does this code print ? Kaz Kylheku <864-117-4973@kylheku.com> - 2023-10-14 02:36 +0000
              Re: What does this code print ? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2023-10-13 20:44 -0700
              Re: What does this code print ? Paavo Helde <eesnimi@osa.pri.ee> - 2023-10-14 11:51 +0300
                Re: What does this code print ? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2023-10-17 11:35 -0700
                Re: What does this code print ? Kaz Kylheku <864-117-4973@kylheku.com> - 2023-10-17 20:06 +0000
                Re: What does this code print ? Paavo Helde <eesnimi@osa.pri.ee> - 2023-10-18 11:43 +0300
                Re: What does this code print ? Kaz Kylheku <864-117-4973@kylheku.com> - 2023-10-18 17:29 +0000
                Re: What does this code print ? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2023-10-18 11:31 -0700
                Re: What does this code print ? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2023-10-19 14:43 -0700
          Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-14 15:54 +0200
            Re: What does this code print ? Kaz Kylheku <864-117-4973@kylheku.com> - 2023-10-14 18:05 +0000
              Re: What does this code print ? Richard Damon <richard@damon-family.org> - 2023-10-14 14:58 -0400
              Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-15 08:58 +0200
        Re: What does this code print ? Richard Damon <news.x.richarddamon@xoxy.net> - 2023-10-14 12:47 -0400
          Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-15 09:07 +0200
            Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-15 09:12 +0200
              Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-15 09:16 +0200
                Re: What does this code print ? Richard Damon <richard@damon-family.org> - 2023-10-15 13:35 -0400
                Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-17 07:48 +0200
                Re: What does this code print ? Richard Damon <richard@damon-family.org> - 2023-10-17 23:04 -0400
                Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-19 19:58 +0200
                Re: What does this code print ? Richard Damon <richard@damon-family.org> - 2023-10-19 14:39 -0400
                Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-19 19:58 +0200
                Re: What does this code print ? Kaz Kylheku <864-117-4973@kylheku.com> - 2023-10-19 18:06 +0000
                Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-19 20:11 +0200
                Re: What does this code print ? Kaz Kylheku <864-117-4973@kylheku.com> - 2023-10-19 19:20 +0000
                Re: What does this code print ? Richard Damon <richard@damon-family.org> - 2023-10-19 16:06 -0400
                Re: What does this code print ? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2023-10-19 14:45 -0700
                Re: What does this code print ? Kaz Kylheku <864-117-4973@kylheku.com> - 2023-10-19 23:26 +0000
                Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-20 09:19 +0200
                Re: What does this code print ? Richard Damon <richard@damon-family.org> - 2023-10-20 05:47 -0400
                Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-20 17:59 +0200
                Re: What does this code print ? Richard Damon <richard@damon-family.org> - 2023-10-20 19:16 -0700
                Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-21 08:02 +0200
                Re: What does this code print ? Richard Damon <richard@damon-family.org> - 2023-10-21 08:38 -0700
                Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-21 19:40 +0200
                Re: What does this code print ? Richard Damon <richard@damon-family.org> - 2023-10-21 10:54 -0700
                Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-21 20:34 +0200
                Re: What does this code print ? Richard Damon <richard@damon-family.org> - 2023-10-21 12:45 -0700
                Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-22 04:18 +0200
                Re: What does this code print ? Richard Damon <richard@damon-family.org> - 2023-10-21 19:28 -0700
                Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-22 06:53 +0200
                Re: What does this code print ? Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2023-10-22 09:59 +0000
                Re: What does this code print ? Richard Damon <richard@damon-family.org> - 2023-10-22 07:12 -0700
                Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-23 19:05 +0200
                Re: What does this code print ? Richard Damon <richard@damon-family.org> - 2023-10-23 10:40 -0700
                Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-24 16:03 +0200
                Re: What does this code print ? Richard Damon <richard@damon-family.org> - 2023-10-24 07:28 -0700
                Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-24 17:01 +0200
                Re: What does this code print ? Richard Damon <richard@damon-family.org> - 2023-10-24 08:28 -0700
                Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-24 18:27 +0200
                Re: What does this code print ? Richard Damon <richard@damon-family.org> - 2023-10-24 10:05 -0700
                Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-24 19:08 +0200
                Re: What does this code print ? Richard Damon <richard@damon-family.org> - 2023-10-24 10:39 -0700
                Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-24 20:25 +0200
                Re: What does this code print ? Kaz Kylheku <864-117-4973@kylheku.com> - 2023-10-24 19:48 +0000
                Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-25 10:54 +0200
                Re: What does this code print ? Richard Damon <richard@damon-family.org> - 2023-10-25 08:43 -0700
                Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-25 17:57 +0200
                Re: What does this code print ? Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2023-10-24 16:40 +0000
                Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-24 19:07 +0200
                Re: What does this code print ? scott@slp53.sl.home (Scott Lurndal) - 2023-10-24 15:25 +0000
                Re: What does this code print ? Richard Damon <richard@damon-family.org> - 2023-10-24 08:34 -0700
                Re: What does this code print ? Kaz Kylheku <864-117-4973@kylheku.com> - 2023-10-24 16:34 +0000
                Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-24 19:05 +0200
                Re: What does this code print ? Kaz Kylheku <864-117-4973@kylheku.com> - 2023-10-20 14:50 +0000
                Re: What does this code print ? Bo Persson <bo@bo-persson.se> - 2023-10-20 17:34 +0200
                Re: What does this code print ? Kaz Kylheku <864-117-4973@kylheku.com> - 2023-10-20 15:59 +0000
                Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-20 18:00 +0200
                Re: What does this code print ? Kaz Kylheku <864-117-4973@kylheku.com> - 2023-10-20 16:06 +0000
                Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-20 18:40 +0200
                Re: What does this code print ? gazelle@shell.xmission.com (Kenny McCormack) - 2023-10-20 20:07 +0000
                Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-21 08:04 +0200
              Re: What does this code print ? Richard Damon <richard@damon-family.org> - 2023-10-15 13:35 -0400
                Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-17 07:50 +0200
                Re: What does this code print ? Richard Damon <richard@damon-family.org> - 2023-10-17 23:08 -0400
                Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-19 20:02 +0200
                Re: What does this code print ? Richard Damon <richard@damon-family.org> - 2023-10-19 14:43 -0400
                Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-19 20:02 +0200
            Re: What does this code print ? scott@slp53.sl.home (Scott Lurndal) - 2023-10-15 14:36 +0000
              Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-15 18:15 +0200
                Re: What does this code print ? Richard Damon <news.x.richarddamon@xoxy.net> - 2023-10-15 22:23 -0400
                Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-17 07:51 +0200
                Re: What does this code print ? Richard Damon <richard@damon-family.org> - 2023-10-17 23:08 -0400
            Re: What does this code print ? Richard Damon <richard@damon-family.org> - 2023-10-15 13:25 -0400
        Re: What does this code print ? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2023-10-14 11:33 -0700
          Re: What does this code print ? Paavo Helde <eesnimi@osa.pri.ee> - 2023-10-14 21:54 +0300
            Re: What does this code print ? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2023-10-14 11:56 -0700
            Re: What does this code print ? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2023-10-24 15:53 -0700
              Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-25 15:07 +0200
                Re: What does this code print ? Richard Damon <richard@damon-family.org> - 2023-10-25 08:43 -0700
                Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-25 18:01 +0200
                Re: What does this code print ? Richard Damon <richard@damon-family.org> - 2023-10-25 09:21 -0700
                Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-25 18:24 +0200
                Re: What does this code print ? Richard Damon <richard@damon-family.org> - 2023-10-25 11:23 -0700
                Re: What does this code print ? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2023-10-25 15:02 -0700
                Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-26 07:13 +0200
                Re: What does this code print ? Richard Damon <richard@damon-family.org> - 2023-10-25 23:09 -0700
                Re: What does this code print ? James Kuyper <jameskuyper@alumni.caltech.edu> - 2023-10-25 23:55 -0400
                Re: What does this code print ? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2023-10-25 15:01 -0700
                Re: What does this code print ? Bonita Montero <Bonita.Montero@gmail.com> - 2023-10-26 07:15 +0200
                Re: What does this code print ? Richard Damon <richard@damon-family.org> - 2023-10-25 23:12 -0700

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