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Date: Wed, 26 Jan 2011 18:13:58 +0200
From: Avi Kivity <avi@redhat.com>
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Subject: Re: [Qemu-devel] [RFC][PATCH 01/12] coroutine: Add gtk-vnc coroutines
	library
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To: Anthony Liguori <aliguori@linux.vnet.ibm.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Anthony Liguori <aliguori@us.ibm.com>, Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>, qemu-devel@nongnu.org

On 01/26/2011 06:00 PM, Anthony Liguori wrote:
> On 01/26/2011 09:25 AM, Avi Kivity wrote:
>> On 01/22/2011 11:29 AM, Stefan Hajnoczi wrote:
>>> Asynchronous image format code is becoming very complex.  Let's try
>>> using coroutines to write sequential code without callbacks but use
>>> coroutines to switch stacks under the hood.
>>>
>>>
>>> +
>>> +int cc_swap(struct continuation *from, struct continuation *to)
>>> +{
>>> +    to->exited = 0;
>>> +    if (getcontext(&to->last) == -1)
>>> +        return -1;
>>> +    else if (to->exited == 0)
>>> +        to->exited = 1;
>>> +    else if (to->exited == 1)
>>> +        return 1;
>>> +
>>> +    return swapcontext(&from->uc,&to->uc);
>>> +}
>>
>> swapcontext() is very slow, involving the fpu and a syscall.
>>
>> A nice trick I've used in the past is to use getcontext/makecontext 
>> for the initial setup and setjmp/longjmp for switching.  Of course 
>> this can be done later, as an optimization.
>
> Yeah, there are further optimizations that can be had but really, it's 
> not important here.  In fact, I'd rather start with the threaded 
> version just because it's far more portable than ucontext.
>

What do you mean by threaded version?

-- 
error compiling committee.c: too many arguments to function