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Re: std::thread does not follow RAII principles

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On 28/05/2021 12:52, Öö Tiib wrote:
> On Thursday, 27 May 2021 at 21:00:13 UTC+3, Chris Vine wrote:
>>
>> One other thing POSIX provides and C++11 doesn't is thread cancellation.
>> Some programmers who don't have relevant experience think thread
>> cancellation is a bad idea because it allows arbitrary cancellation
>> which cannot be adequately controlled (the "combing your hair with a
>> fork" jibe). Whilst that is true with windows it absolutely isn't with
>> POSIX. What you do is use deferred cancellation (the default in POSIX)
>> and block cancellation as normal policy, and only enable cancellation
>> at defined points in the code which are able to deal with it (normally
>> where a wait is to occur). Done properly, thread cancellation is far
>> easier to use than exceptions, which can jump out of anywhere if you
>> include std::bad_alloc in the mix. C++11 threads don't deal with
>> cancellation and will never be able to do so because they require OS
>> support - in this case POSIX support.
> 
> With that thread cancellation I'm always in doubt. Especially if discussed
> in context of RAII and destructor of thing like std::thread.
> 
> One of major reasons making a thread is to turn synchronous work into
> asynchronous. For that we put it into thread so then synchronous work is
> going on in thread doing its blocking operations (potentially checking if
> the work has become obsolete and/or reporting progress between those)
> and once complete (or failed) handing the results back over to caller thread.
> That way the caller thread has all benefits of asynchronous works going on.
> It is fully responsive, so can take care of other responsibilities, entertain
> users, report progresses, mark ongoing works obsolete and/or put out the
> results (or failures) once something becomes complete.
> 
> But what is that cancellation? It is like telling to worker thread to die in
> middle of unknown state potentially in kernel with unknown amount of
> locks taken, files open or mapped to virtual memory, that fragile external
> hardware device produced by random morons in middle of something
> and what not? std::terminate feels better and more honest than to cancel
> the thread ... at least our users will see that we screwed all up in major
> way. It all gets of course lost in examples because these talk about "foo()".

Cancellation is well defined in POSIX.  Cancellation points are defined 
by the standard and threads can manage their own cancellation type and 
state,

If you want to manage resources in a thread that may be cancelled, you 
can use cleanup functions.  I haven't tried it in Linux, but certainly 
in Solaris, the C++ runtime will destroy objects if the creating thread 
is cancelled.  This is one of those annoying behaviours not covered by 
either the C++ or POSIX standards...

A quick check on Linux shows that yes, destructors are called when a 
thread is cancelled.

-- 
Ian

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Re: std::thread does not follow RAII principles MrSpook_ry@939_6htz773e0qeya.eu - 2021-05-27 08:18 +0000
  Re: std::thread does not follow RAII principles Bonita Montero <Bonita.Montero@gmail.com> - 2021-05-27 11:02 +0200
    Re: std::thread does not follow RAII principles MrSpook_b28s@jxgz6zklebr1.tv - 2021-05-27 10:24 +0000
      Re: std::thread does not follow RAII principles Bonita Montero <Bonita.Montero@gmail.com> - 2021-05-27 12:33 +0200
        Re: std::thread does not follow RAII principles Bonita Montero <Bonita.Montero@gmail.com> - 2021-05-27 12:40 +0200
          Re: std::thread does not follow RAII principles Bonita Montero <Bonita.Montero@gmail.com> - 2021-05-27 12:55 +0200
        Re: std::thread does not follow RAII principles MrSpook_d4c3Jb7l7@8dftupdzk09cop2.co.uk - 2021-05-27 11:05 +0000
          Re: std::thread does not follow RAII principles Bonita Montero <Bonita.Montero@gmail.com> - 2021-05-27 13:14 +0200
            Re: std::thread does not follow RAII principles Bonita Montero <Bonita.Montero@gmail.com> - 2021-05-27 13:18 +0200
            Re: std::thread does not follow RAII principles MrSpook_b_x@ukpge.org - 2021-05-27 15:54 +0000
              Re: std::thread does not follow RAII principles Bonita Montero <Bonita.Montero@gmail.com> - 2021-05-27 19:32 +0200
                Re: std::thread does not follow RAII principles Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2021-05-27 19:00 +0100
                Re: std::thread does not follow RAII principles Öö Tiib <ootiib@hot.ee> - 2021-05-27 17:52 -0700
                Re: std::thread does not follow RAII principles Bonita Montero <Bonita.Montero@gmail.com> - 2021-05-28 05:24 +0200
                Re: std::thread does not follow RAII principles Bonita Montero <Bonita.Montero@gmail.com> - 2021-05-28 05:27 +0200
                Re: std::thread does not follow RAII principles Ian Collins <ian-news@hotmail.com> - 2021-05-28 14:59 +1200
                Re: std::thread does not follow RAII principles Öö Tiib <ootiib@hot.ee> - 2021-05-27 20:37 -0700
                Re: std::thread does not follow RAII principles Ian Collins <ian-news@hotmail.com> - 2021-05-28 16:50 +1200
                Re: std::thread does not follow RAII principles Bonita Montero <Bonita.Montero@gmail.com> - 2021-05-28 06:53 +0200
                Re: std::thread does not follow RAII principles Öö Tiib <ootiib@hot.ee> - 2021-05-27 23:07 -0700
                Re: std::thread does not follow RAII principles Bonita Montero <Bonita.Montero@gmail.com> - 2021-05-28 08:26 +0200
                Re: std::thread does not follow RAII principles Ian Collins <ian-news@hotmail.com> - 2021-05-28 21:01 +1200
                Re: std::thread does not follow RAII principles Bonita Montero <Bonita.Montero@gmail.com> - 2021-05-28 13:04 +0200
                Re: std::thread does not follow RAII principles Branimir Maksimovic <branimir.maksimovic@gmail.com> - 2021-05-28 17:06 +0000
                Re: std::thread does not follow RAII principles scott@slp53.sl.home (Scott Lurndal) - 2021-05-28 17:51 +0000
                Re: std::thread does not follow RAII principles Bonita Montero <Bonita.Montero@gmail.com> - 2021-05-28 20:00 +0200
                Re: std::thread does not follow RAII principles Branimir Maksimovic <branimir.maksimovic@gmail.com> - 2021-05-28 21:42 +0000
                Re: std::thread does not follow RAII principles Branimir Maksimovic <branimir.maksimovic@gmail.com> - 2021-05-28 17:03 +0000
                Re: std::thread does not follow RAII principles Bonita Montero <Bonita.Montero@gmail.com> - 2021-05-28 03:55 +0200
                Re: std::thread does not follow RAII principles Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2021-05-28 12:02 +0100
                Re: std::thread does not follow RAII principles Bonita Montero <Bonita.Montero@gmail.com> - 2021-05-28 13:15 +0200
                Re: std::thread does not follow RAII principles Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2021-05-28 12:40 +0100
                Re: std::thread does not follow RAII principles Bonita Montero <Bonita.Montero@gmail.com> - 2021-05-28 13:55 +0200
                Re: std::thread does not follow RAII principles Bonita Montero <Bonita.Montero@gmail.com> - 2021-05-28 13:57 +0200
                Re: std::thread does not follow RAII principles Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2021-05-28 14:29 +0100
                Re: std::thread does not follow RAII principles Bonita Montero <Bonita.Montero@gmail.com> - 2021-05-28 15:48 +0200
                Re: std::thread does not follow RAII principles Bonita Montero <Bonita.Montero@gmail.com> - 2021-05-28 16:16 +0200
                Re: std::thread does not follow RAII principles Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2021-05-28 15:45 +0100
                Re: std::thread does not follow RAII principles Bonita Montero <Bonita.Montero@gmail.com> - 2021-05-28 17:30 +0200
                Re: std::thread does not follow RAII principles Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2021-05-28 19:54 +0100
                Re: std::thread does not follow RAII principles Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2021-05-28 15:08 +0100
                Re: std::thread does not follow RAII principles Branimir Maksimovic <branimir.maksimovic@gmail.com> - 2021-05-28 17:08 +0000
                Re: std::thread does not follow RAII principles Öö Tiib <ootiib@hot.ee> - 2021-05-29 01:42 -0700
                Re: std::thread does not follow RAII principles Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2021-05-29 13:05 +0100
                Re: std::thread does not follow RAII principles Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2021-05-29 13:44 +0100
                Re: std::thread does not follow RAII principles Öö Tiib <ootiib@hot.ee> - 2021-05-29 06:34 -0700
                Re: std::thread does not follow RAII principles Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2021-05-29 14:48 +0100
                Re: std::thread does not follow RAII principles Öö Tiib <ootiib@hot.ee> - 2021-05-29 07:59 -0700
                Re: std::thread does not follow RAII principles Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2021-05-29 18:15 +0100
                Re: std::thread does not follow RAII principles Öö Tiib <ootiib@hot.ee> - 2021-05-29 19:03 -0700
                Re: std::thread does not follow RAII principles Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2021-05-30 11:48 +0100
                Re: std::thread does not follow RAII principles Öö Tiib <ootiib@hot.ee> - 2021-05-30 09:35 -0700
                Re: std::thread does not follow RAII principles Öö Tiib <ootiib@hot.ee> - 2021-05-29 06:51 -0700
                Re: std::thread does not follow RAII principles MrSpook_jx@zp238i0_j1.net - 2021-05-28 11:11 +0000

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