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From: "vc" <>
To: "Simon Gerblich" <>
Cc: <>
Subject: Re: problem using pthread_cancel and pthread_mutex_lock
Date: Thu, 26 Feb 2004 15:59:00 -0000	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

Thanks to all of you for your answers.

----- Original Message -----
From: "Simon Gerblich" <>
To: "vc" <>
Cc: <>
Sent: Tuesday, February 24, 2004 5:23 AM
Subject: RE: problem using pthread_cancel and pthread_mutex_lock

> Hi Viv,
> >So, my question is: how can a thread cleanly cancel another thread
> >which is waiting in a 'pthread_mutex_lock' call, so that this mutex is
> >available again ?
> I can see a few problems in what you are doing.
> A mutex is not really designed to be locked in a thread for a long time
> unlocked by another thread.  When I use a mutex in a thread I lock it - do
> what I have to do  - and then unlock it ASAP.  I don't use mutexes to
> synchronise threads.  I use them to protect data.  Pthread mutexes are not
> cancellation points.
> I use deferred cancellation instead of asynchronous cancellation because
> recommendations in "Programming with POSIX Threads" by David Butenhof.
> Page 150 "Avoid asynchronous cancellation.  It is difficult to use
> and is rarely useful."
> Page 151 "Asynchronous cancellation can occur at any hardware instruction.
> On some computers it may even be possible to interrupt some instructions
> the middle.  That makes it really difficult to determine what the canceled
> thread was doing."
> Page 151 "Call no code with asynchronous cancellation enabled unless you
> wrote it to be async-cancel safe - and even then, think twice!"
> I write my applications with deferred cancellation and the threads
> on message queues, which are cancellation points.  When a cancel is
> requested the threads exit cleanly when they next go to read the message
> queue.  I have minimal cancellation points in my code so that I know
> where my threads will cancel.
> Without knowing exactly what you are trying to do I think you should have
> look at using a condition variable instead of a mutex for your thread
> syncing.  Waiting on a condition variable is a cancellation point.
> Be aware that the Sleep() function on windows is not a cancellation point.
> I have written my own sleep functions to use with pthreads-win32 that
> on condition variables with timeouts.
> If your not lurking in the google groups comp.programming.threads I'd
> recommend it.  I've learnt a lot following threads on pthreads, etc.
> Cheers,
> Simon

  reply	other threads:[~2004-02-26 15:59 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2004-02-24  4:23 Simon Gerblich
2004-02-26 15:59 ` vc [this message]
  -- strict thread matches above, loose matches on Subject: below --
2004-03-09 23:25 Simon Gerblich
2004-03-10  0:57 ` Will Bryant
2004-03-10 11:11 ` vc
2004-02-23 17:43 vc
2004-03-01 16:27 ` vc
2004-03-04 23:13   ` Ross Johnson
2004-03-09 14:06     ` vc
2004-03-09 14:15     ` Brano Kemen
2004-03-09 15:09       ` Panagiotis E. Hadjidoukas
2004-03-09 15:42         ` Brano Kemen

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