Re: [Qemu-devel] [PATCH v8 0/5] Coroutines for better asynchronous programming

[Stefan Hajnoczi]

On Tue, Jul 26, 2011 at 10:21 AM, Stefan Hajnoczi
<address@hidden> wrote:
> QEMU is event-driven and suffers when blocking operations are performed 
> because
> VM execution may be stopped until the operation completes.  Therefore many
> operations that could block are performed asynchronously and a callback is
> invoked when the operation has completed.  This allows QEMU to continue
> executing while the operation is pending.
>
> The downside to callbacks is that they split up code into many smaller
> functions, each of which is a single step in a state machine that quickly
> becomes complex and hard to understand.  Callback functions also result in 
> lots
> of noise as variables are packed and unpacked into temporary structs that pass
> state to the callback function.
>
> This patch series introduces coroutines as a solution for writing asynchronous
> code while still having a nice sequential control flow.  The semantics are
> explained in the second patch.  The fourth patch adds automated tests.
>
> A nice feature of coroutines is that it is relatively easy to take synchronous
> code and lift it into a coroutine to make it asynchronous.  Work has been done
> to move qcow2 request processing into coroutines and thereby make it
> asynchronous (today qcow2 will perform synchronous metadata accesses).  This
> qcow2 work is still ongoing and not quite ready for mainline yet.
>
> v8:
>  * Bisectability: introduce gthread implementation before ucontext/fibers

Aneesh's code on top of this will go in separately.

We're good to go.

Stefan