Re: [boost] [asio-users] Cancelation not working on windows?

From: McCabe, David (david.mccabe_at_[hidden])
Date: 2008-02-05 06:37:34

I'm going to go out on a limb here, because I don't have asio's source
to hand, but...

CancelIo (per
<<http://msdn2.microsoft.com/en-us/library/aa363791(VS.85).aspx>>
cancels "all pending input and output (I/O) operations that are issued
by the calling thread for the specified file." Since you're cancelling
on a different thread, I assume asio calls CancelIo on that thread and
thus doesn't cancel the operation. See Larry Osterman's blog
<<http://blogs.msdn.com/larryosterman/archive/2004/03/19/92857.aspx>>
for background.

Vista offers CancelIoEx and CancelSynchronousIo for these situations,
but on previous versions of Windows there's no way to cancel I/O going
on in a different thread.

David

-----Original Message-----
From: Roland Schwarz [mailto:roland.schwarz_at_[hidden]] 
Sent: Monday, 4 February 2008 7:46 AM
To: asio-users_at_[hidden]; boost_at_[hidden]; Christopher
Kohlhoff
Subject: Re: [boost] [asio-users] Cancelation not working on windows?

This is my second attempt, since there was no
meaningful answer on the first.

I again apologize for cross-posting but I still
have no idea which is the correct list to post asio
related questions.

Roland Schwarz wrote:
> One of my objectives is getting cancellation in a
> platform independent way. Since on windows blocking
> io cannot be canceled I tried to use asio to emulate
> the required behavior.
> 
> This works well on linux, but the same code fails
> on windows. During a debug session it appeared to me
> as if the CancelIO call is not being honored (WindowsXP).
> 
> Is this a bug in asio or am I doing something wrong.
> 
> I put together a stripped down example to show
> the "erroneous" behavior.
> 
> The examples main thread connects to localhost port 80 and
> then schedules an async read call.
> 
> A second polling thread checks for ctrl-c beeing pressed
> and invokes the sockets cancel function.
> 
> On linux this causes the read handler to terminate with
> Oeration Cancelled
> as expected, but on windows the cancel request is simply
> swallowed.
> 
> Any help appreciated!
> 

-- 
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