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

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

On Fri, Apr 1, 2011 at 7:27 PM, Johannes Sixt [off-list ref] wrote:

quoted

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

quoted

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.

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