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Date: Thu, 14 Oct 2010 11:19:37 +0200
From: Gleb Natapov <gleb@redhat.com>
Subject: Re: [Qemu-devel] [PATCH 1/3] Introduce threadlets
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To: Stefan Hajnoczi <stefanha@gmail.com>
Cc: Arun R Bharadwaj <arun@linux.vnet.ibm.com>, qemu-devel@nongnu.org

On Thu, Oct 14, 2010 at 10:15:30AM +0100, Stefan Hajnoczi wrote:
> I forgot to add that the semantics of cancellation make it difficult
> to write correct user code.  Every cancellation user needs to add
> extra synchronization after the cancel call to handle the case where
> the work is currently executing.
> 
> This seems tricky to me and I suspect code using this interface will
> be buggy.  How about the following?
> 1. Add a return value indicating that the work is currently executing
> (this still requires the caller to add extra synchronization but is at
> least explicit) versus work is no longer on the list.
> 2. Add a flag to block until the work has been cancelled or completed.
>  This is useful to callers who are allowed to block.
> 
In Linux kernel you usually have two function cancel() and
cancel_sync(). Second variant waits for work completion.

--
			Gleb.