Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.c++ > #4951

Re: Please disprove this Double-Checked Locking "fix"

From Gerhard Fiedler <gelists@gmail.com>
Subject Re: Please disprove this Double-Checked Locking "fix"
Newsgroups comp.lang.c++
References <78f3178b-efdc-4af5-8f84-7ff6fa995af7@e25g2000prf.googlegroups.com> <d6774102-147b-4e3d-a457-a6bfd4c98a13@f15g2000pro.googlegroups.com> <5b81d426-bc25-46b2-b97d-0ea29355dcb1@z13g2000prk.googlegroups.com>
Date 2011-05-13 19:56 -0300
Message-ID <1bzq6ymjbt91c$.dlg@gelists.gmail.com> (permalink)
Organization Unlimited download news at news.astraweb.com

Show all headers | View raw

Joshua Maurice wrote:

> However, a sufficiently smart compiler could notice your clever ruse,
> optimize away the assert as always true, see a lock and unlock pair
> guarding nothing, optimize that away, and then move the assignment to
> temp past the mutex acquire, as demonstrated above.

Regarding the compiler optimizing away a lock/unlock pair guarding
"nothing": AIUI both lock and unlock need to provide certain fences.
Therefore, again AIUI, they can't be optimized away by the compiler even
if there's nothing in between, because that would remove the fences and
alter the behavior. 

Am I missing something here?

Gerhard

Back to comp.lang.c++ | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Please disprove this Double-Checked Locking "fix" jl_post@hotmail.com - 2011-04-26 09:58 -0700
  Re: Please disprove this Double-Checked Locking "fix" Leigh Johnston <leigh@i42.co.uk> - 2011-04-26 18:17 +0100
  Re: Please disprove this Double-Checked Locking "fix" Pete Becker <pete@versatilecoding.com> - 2011-04-26 13:50 -0400
    Re: Please disprove this Double-Checked Locking "fix" Scott Meyers <NeverRead@aristeia.com> - 2011-05-01 17:14 -0700
      Re: Please disprove this Double-Checked Locking "fix" Joshua Maurice <joshuamaurice@gmail.com> - 2011-05-02 15:59 -0700
        Re: Please disprove this Double-Checked Locking "fix" Pete Becker <pete@versatilecoding.com> - 2011-05-03 08:39 -0400
  Re: Please disprove this Double-Checked Locking "fix" Joshua Maurice <joshuamaurice@gmail.com> - 2011-04-26 11:16 -0700
    Re: Please disprove this Double-Checked Locking "fix" Joshua Maurice <joshuamaurice@gmail.com> - 2011-04-26 11:19 -0700
    Re: Please disprove this Double-Checked Locking "fix" Pete Becker <pete@versatilecoding.com> - 2011-04-26 14:30 -0400
      Re: Please disprove this Double-Checked Locking "fix" Joshua Maurice <joshuamaurice@gmail.com> - 2011-04-26 11:50 -0700
    Re: Please disprove this Double-Checked Locking "fix" Joshua Maurice <joshuamaurice@gmail.com> - 2011-05-11 19:55 -0700
      Re: Please disprove this Double-Checked Locking "fix" Gerhard Fiedler <gelists@gmail.com> - 2011-05-13 19:56 -0300
        Re: Please disprove this Double-Checked Locking "fix" Joshua Maurice <joshuamaurice@gmail.com> - 2011-05-13 16:59 -0700
          Re: Please disprove this Double-Checked Locking "fix" Gerhard Fiedler <gelists@gmail.com> - 2011-05-18 18:12 -0300
            Re: Please disprove this Double-Checked Locking "fix" Joshua Maurice <joshuamaurice@gmail.com> - 2011-05-18 14:53 -0700
              Re: Please disprove this Double-Checked Locking "fix" Gerhard Fiedler <gelists@gmail.com> - 2011-05-19 13:46 -0300
                Re: Please disprove this Double-Checked Locking "fix" Joshua Maurice <joshuamaurice@gmail.com> - 2011-05-19 15:30 -0700
                Re: Please disprove this Double-Checked Locking "fix" Gerhard Fiedler <gelists@gmail.com> - 2011-05-21 11:55 -0300
                Re: Please disprove this Double-Checked Locking "fix" Joshua Maurice <joshuamaurice@gmail.com> - 2011-05-22 01:08 -0700
  Re: Please disprove this Double-Checked Locking "fix" James Kanze <james.kanze@gmail.com> - 2011-04-30 15:54 -0700
    Re: Please disprove this Double-Checked Locking "fix" Leigh Johnston <leigh@i42.co.uk> - 2011-05-01 21:49 +0100
      Re: Please disprove this Double-Checked Locking "fix" Pavel <pauldontspamtolk@removeyourself.dontspam.yahoo> - 2011-05-01 17:26 -0400
        Re: Please disprove this Double-Checked Locking "fix" Leigh Johnston <leigh@i42.co.uk> - 2011-05-01 22:44 +0100
          Re: Please disprove this Double-Checked Locking "fix" Leigh Johnston <leigh@i42.co.uk> - 2011-05-02 01:01 +0100
            Re: Please disprove this Double-Checked Locking "fix" Pavel <pauldontspamtolk@removeyourself.dontspam.yahoo> - 2011-05-01 22:04 -0400
            Re: Please disprove this Double-Checked Locking "fix" "Chris M. Thomasson" <cristom@charter.net> - 2011-05-04 11:49 -0700
              Re: Please disprove this Double-Checked Locking "fix" Pavel <pauldontspamtolk@removeyourself.dontspam.yahoo> - 2011-05-06 00:16 -0400
          Re: Please disprove this Double-Checked Locking "fix" Joshua Maurice <joshuamaurice@gmail.com> - 2011-05-02 15:43 -0700
        Re: Please disprove this Double-Checked Locking "fix" James Kanze <james.kanze@gmail.com> - 2011-05-01 14:53 -0700
          Re: Please disprove this Double-Checked Locking "fix" Pavel <pauldontspamtolk@removeyourself.dontspam.yahoo> - 2011-05-01 19:23 -0400
            Re: Please disprove this Double-Checked Locking "fix" James Kanze <james.kanze@gmail.com> - 2011-05-02 09:02 -0700
              Re: Please disprove this Double-Checked Locking "fix" Pavel <pauldontspamtolk@removeyourself.dontspam.yahoo> - 2011-05-05 23:46 -0400
      Re: Please disprove this Double-Checked Locking "fix" James Kanze <james.kanze@gmail.com> - 2011-05-01 14:47 -0700

csiph-web