Re: threading

From	Marko Rauhamaa <marko@pacujo.net>
Newsgroups	comp.lang.python
Subject	Re: threading
Date	2014-04-08 08:19 +0300
Organization	A noiseless patient Spider
Message-ID	<877g70wg8p.fsf@elektro.pacujo.net> (permalink)
References	<CAChsEZTGWa9Rxhwwg=b8Cnn3tx7FiaWqTJvHRn8hatxmVhOv0A@mail.gmail.com> <mailman.8969.1396839923.18130.python-list@python.org> <87d2gt4td2.fsf@elektro.pacujo.net> <7xha651yx2.fsf@ruckus.brouhaha.com> <mailman.8986.1396914468.18130.python-list@python.org>

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Dennis Lee Bieber <wlfraed@ix.netcom.com>:

> 	That's been my experience too... Threading works for me... My
> attempts at so called asyncio (whatever language) have always led to
> my having to worry about losing data if some handler takes too long to
> return.
>
> 	To me, asyncio is closer to a polling interrupt handler, and I
> still need a thread to handle the main processing.

Yes, asynchronous processing results in complex, event-driven state
machines that can be hard to get right. However, my experience is that
that's the lesser evil.

About a handler taking too long: you need to guard each state with a
timer. Also, you need then to handle the belated handler after the timer
has expired.

The main problems with threads include:

 * Thread-safety is rarely done right. Also, when it's done wrong, it
   can be virtually impossible to fix it without a significant rewrite.
   This is not a theoretical concern: I have had to deal with the
   resulting nightmares in my work.

 * There is no accepted, taught, industry-wide discipline on proper
   thread-safety practices so every developer has to improvise. I have
   come up with a "bullet-proof" way of developing with threads, but
   even that methodology has nasty corner cases.

 * Thread-safety cannot be abstracted out. IOW, divide and conquer
   doesn't work. You can't hide the locking inside a class and forget
   about it. The entire application must be aware low-level thread
   synchronization needs.

 * Threads assume each state has one exit event. At a bare minimum, each
   thread should be prepared to have the blocking event aborted from the
   outside. Unfortunately, most threading frameworks don't allow for
   graceful aborts (that goes for Java and Python, too).

 * If you have made your design around threads and finally decide
   asynchronous processing would have been a better choice, a complete
   rewrite is required if it is even possible. Library writers often
   only provide blocking I/O functions forcing you to insulate the
   libraries in thread pools.


Marko

Thread

Re: threading Ben Finney <ben+python@benfinney.id.au> - 2014-04-07 13:05 +1000
  Re: threading Roy Smith <roy@panix.com> - 2014-04-06 23:48 -0400
    Re: threading Chris Angelico <rosuav@gmail.com> - 2014-04-07 13:56 +1000
      Re: threading Roy Smith <roy@panix.com> - 2014-04-07 08:26 -0400
        Re: threading Chris Angelico <rosuav@gmail.com> - 2014-04-07 22:34 +1000
          Re: threading Roy Smith <roy@panix.com> - 2014-04-07 09:22 -0400
            Re: threading Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-04-07 14:41 +0100
            Re: threading Marko Rauhamaa <marko@pacujo.net> - 2014-04-07 16:49 +0300
              Re: threading Chris Angelico <rosuav@gmail.com> - 2014-04-08 00:27 +1000
                Re: threading Marko Rauhamaa <marko@pacujo.net> - 2014-04-07 17:51 +0300
                Re: threading Chris Angelico <rosuav@gmail.com> - 2014-04-08 01:12 +1000
            Re: threading Chris Angelico <rosuav@gmail.com> - 2014-04-08 00:24 +1000
      Re: threading Rick Johnson <rantingrickjohnson@gmail.com> - 2014-04-08 18:09 -0700
        Re: threading "Neil D. Cerutti" <neilc@norwich.edu> - 2014-04-09 09:50 -0400
          Re: threading Rick Johnson <rantingrickjohnson@gmail.com> - 2014-04-09 08:51 -0700
            Re: threading MRAB <python@mrabarnett.plus.com> - 2014-04-09 18:47 +0100
              Re: threading Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-04-10 11:35 +1200
                Re: threading Roy Smith <roy@panix.com> - 2014-04-09 19:53 -0400
                Re: threading Andrew Berg <robotsondrugs@gmail.com> - 2014-04-09 19:02 -0500
                Re: threading Steven D'Aprano <steve@pearwood.info> - 2014-04-10 02:43 +0000
                Re: threading Chris Angelico <rosuav@gmail.com> - 2014-04-10 13:08 +1000
                Re: threading Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-04-10 09:23 +0100
                Re: threading Chris Angelico <rosuav@gmail.com> - 2014-04-10 19:11 +1000
            Re: threading Chris Angelico <rosuav@gmail.com> - 2014-04-10 04:00 +1000
            Re: threading Steven D'Aprano <steve@pearwood.info> - 2014-04-10 03:44 +0000
              Re: threading Chris Angelico <rosuav@gmail.com> - 2014-04-10 13:54 +1000
    Re: threading Ben Finney <ben+python@benfinney.id.au> - 2014-04-07 15:22 +1000
    Re: threading Ethan Furman <ethan@stoneleaf.us> - 2014-04-08 11:09 -0700
    Re: threading Sturla Molden <sturla.molden@gmail.com> - 2014-04-08 21:41 +0200
      Re: threading Grant Edwards <invalid@invalid.invalid> - 2014-04-08 20:30 +0000
        Re: threading Sturla Molden <sturla.molden@gmail.com> - 2014-04-09 00:32 +0200
          Re: threading Rustom Mody <rustompmody@gmail.com> - 2014-04-08 19:17 -0700
  Re: threading Marko Rauhamaa <marko@pacujo.net> - 2014-04-07 08:10 +0300
    Re: threading Paul Rubin <no.email@nospam.invalid> - 2014-04-06 22:39 -0700
      Re: threading Marko Rauhamaa <marko@pacujo.net> - 2014-04-07 08:46 +0300
      Re: threading Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2014-04-07 19:47 -0400
        Re: threading Marko Rauhamaa <marko@pacujo.net> - 2014-04-08 08:19 +0300
          Re: threading Sturla Molden <sturla.molden@gmail.com> - 2014-04-08 10:47 +0000
            Re: threading Marko Rauhamaa <marko@pacujo.net> - 2014-04-08 15:10 +0300
              Re: threading Sturla Molden <sturla.molden@gmail.com> - 2014-04-08 16:37 +0000
                Re: threading Marko Rauhamaa <marko@pacujo.net> - 2014-04-08 20:17 +0300
            Re: threading Roy Smith <roy@panix.com> - 2014-04-08 09:19 -0400
              Re: threading Sturla Molden <sturla.molden@gmail.com> - 2014-04-08 15:44 +0000
                Re: threading Paul Rubin <no.email@nospam.invalid> - 2014-04-08 09:38 -0700
                Re: threading Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-04-09 14:42 +0100
          Re: threading "Frank Millman" <frank@chagford.com> - 2014-04-09 15:23 +0200
            Re: threading Marko Rauhamaa <marko@pacujo.net> - 2014-04-09 16:55 +0300
              Re: threading "Frank Millman" <frank@chagford.com> - 2014-04-09 16:46 +0200
                Re: threading Marko Rauhamaa <marko@pacujo.net> - 2014-04-09 20:31 +0300
                Re: threading Chris Angelico <rosuav@gmail.com> - 2014-04-10 03:52 +1000
                Re: threading Mark H Harris <harrismh777@gmail.com> - 2014-04-10 08:29 -0500
                Re: threading Sturla Molden <sturla.molden@gmail.com> - 2014-04-09 19:20 +0000
          Re: threading Chris Angelico <rosuav@gmail.com> - 2014-04-09 23:47 +1000
            Re: threading Roy Smith <roy@panix.com> - 2014-04-09 10:44 -0400
          Re: threading "Frank Millman" <frank@chagford.com> - 2014-04-09 16:30 +0200
            Re: threading Roy Smith <roy@panix.com> - 2014-04-09 10:52 -0400
              Re: threading Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-04-10 11:19 +1200
            Re: threading Marko Rauhamaa <marko@pacujo.net> - 2014-04-09 19:48 +0300
          Re: threading Chris Angelico <rosuav@gmail.com> - 2014-04-10 00:44 +1000
          Re: threading Sturla Molden <sturla.molden@gmail.com> - 2014-04-09 15:29 +0000
          Re: threading Terry Reedy <tjreedy@udel.edu> - 2014-04-09 12:14 -0400
          Re: threading Chris Angelico <rosuav@gmail.com> - 2014-04-10 02:25 +1000
          Re: threading Sturla Molden <sturla.molden@gmail.com> - 2014-04-09 16:32 +0000
          Re: threading Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2014-04-09 19:44 -0400
          Re: threading Chris Angelico <rosuav@gmail.com> - 2014-04-10 11:05 +1000
          Re: threading "Frank Millman" <frank@chagford.com> - 2014-04-10 11:17 +0200
          Re: threading Chris Angelico <rosuav@gmail.com> - 2014-04-10 19:40 +1000
          Re: threading "Frank Millman" <frank@chagford.com> - 2014-04-10 13:10 +0200
            Re: threading Marko Rauhamaa <marko@pacujo.net> - 2014-04-10 14:43 +0300
              Re: threading Roy Smith <roy@panix.com> - 2014-04-10 08:56 -0400
              Re: threading Sturla Molden <sturla.molden@gmail.com> - 2014-04-10 15:24 +0000
                Re: threading Marko Rauhamaa <marko@pacujo.net> - 2014-04-10 19:20 +0300
              Re: threading Chris Angelico <rosuav@gmail.com> - 2014-04-11 01:32 +1000
                Re: threading Marko Rauhamaa <marko@pacujo.net> - 2014-04-10 19:25 +0300
                Re: threading Chris Angelico <rosuav@gmail.com> - 2014-04-11 03:08 +1000
                Re: threading Rustom Mody <rustompmody@gmail.com> - 2014-04-10 11:14 -0700
                Re: threading Marko Rauhamaa <marko@pacujo.net> - 2014-04-10 22:44 +0300
                Re: threading Rustom Mody <rustompmody@gmail.com> - 2014-04-10 13:21 -0700
                Re: threading Marko Rauhamaa <marko@pacujo.net> - 2014-04-10 23:44 +0300
                Re: threading Rustom Mody <rustompmody@gmail.com> - 2014-04-10 22:15 -0700
                Re: threading Rustom Mody <rustompmody@gmail.com> - 2014-04-10 23:50 -0700
                Re: threading Marko Rauhamaa <marko@pacujo.net> - 2014-04-11 18:36 +0300
                Re: threading Chris Angelico <rosuav@gmail.com> - 2014-04-12 01:53 +1000
                Re: threading Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-04-11 16:58 +0100
                Re: threading Rustom Mody <rustompmody@gmail.com> - 2014-04-11 11:54 -0700
                Re: threading Marko Rauhamaa <marko@pacujo.net> - 2014-04-11 22:27 +0300
                Re: threading Sturla Molden <sturla.molden@gmail.com> - 2014-04-11 01:51 +0200
                Re: threading Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-04-11 05:35 +0000
                Re: threading Sturla Molden <sturla.molden@gmail.com> - 2014-04-11 09:26 +0000
                Re: threading Roy Smith <roy@panix.com> - 2014-04-11 08:36 -0400
                Re: threading Grant Edwards <invalid@invalid.invalid> - 2014-04-11 16:18 +0000
                Re: threading Sturla Molden <sturla.molden@gmail.com> - 2014-04-11 02:21 +0200
                Re: threading Terry Reedy <tjreedy@udel.edu> - 2014-04-10 20:23 -0400
          Re: threading Chris Angelico <rosuav@gmail.com> - 2014-04-10 21:19 +1000
      Re: threading Sturla Molden <sturla.molden@gmail.com> - 2014-04-08 02:06 +0000
        Re: threading alister <alister.nospam.ware@ntlworld.com> - 2014-04-08 11:07 +0000
          Re: threading Roy Smith <roy@panix.com> - 2014-04-08 09:13 -0400
            Re: threading Chris Angelico <rosuav@gmail.com> - 2014-04-08 23:23 +1000
              Re: threading alister <alister.nospam.ware@ntlworld.com> - 2014-04-08 14:15 +0000
                Re: threading Sturla Molden <sturla.molden@gmail.com> - 2014-04-08 16:06 +0000
            Re: threading Sturla Molden <sturla.molden@gmail.com> - 2014-04-08 15:40 +0000
              Re: threading Paul Rubin <no.email@nospam.invalid> - 2014-04-08 09:46 -0700
                Re: threading Chris Angelico <rosuav@gmail.com> - 2014-04-09 02:46 +1000
                Re: threading Sturla Molden <sturla.molden@gmail.com> - 2014-04-08 17:17 +0000
          Re: threading Sturla Molden <sturla.molden@gmail.com> - 2014-04-08 15:19 +0000

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