Re: [PATCH 5/4] run-command: implement abort_async for pthreads

From: Johannes Sixt <j6t@kdbg.org>
Date: Apr 1, 2011, 19:42 UTC
Message-ID: <201104012142.22065.j6t@kdbg.org>
In-Reply-To: <AANLkTi=8+V3w-1uQgekjntM1qREGZYWSTE_ra1NbDxG8@mail.gmail.com>

On Freitag, 1. April 2011, Erik Faye-Lund wrote:

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> On Fri, Apr 1, 2011 at 7:27 PM, Johannes Sixt <j6t@kdbg.org> wrote:
> > On Freitag, 1. April 2011, Erik Faye-Lund wrote:
> >> OK, I've read up on thread-cancellation, and this code seems correct.
> >> pthread_cancel doesn't kill the thread right away, it just signals a
> >> cancellation-event, which is checked for at certain
> >> cancellation-points. A lot of the CRT functions are defined as
> >> cancellation points, so it'll be a matter for us Win32-guys to
> >> implement pthread_testcancel() and inject that into the
> >> function-wrappers of the CRT functions that are marked as
> >> cancellation-points.
> >
> > That's not going to happen. We cannot implement pthread_cancel() on
> > Windows because it would have to be able to interrupt blocking system
> > calls. (TerminateThread() is a no-no, given all the caveats about leaking
> > system resources that are mentioned in the manual.)
>
> Did you read my suggestion?

Yes, I did.

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> I was talking about implementing 
> cancellation-points, just like on other platforms. This should not
> lead to TerminateThread, but instead a conditional ExitThread from the
> thread in question.
>
> Something like this (I've only added a cancellation-point at close,
> just to illustrate what I mean):

But this does not help the case at hand in any way. How would you interrupt a thread that is blocked in ReadFile()? The point of pthread_cancel() is that it interrupts blocked system calls, something that you cannot achieve if you want to keep using MS's C runtime.

-- Hannes