On 2011-05-11 12:15, Stefan Hajnoczi wrote:
> From: Kevin Wolf <kw...@redhat.com>
>
> Asynchronous code is becoming very complex. At the same time
> synchronous code is growing because it is convenient to write.
> Sometimes duplicate code paths are even added, one synchronous and the
> other asynchronous. This patch introduces coroutines which allow code
> that looks synchronous but is asynchronous under the covers.
>
> A coroutine has its own stack and is therefore able to preserve state
> across blocking operations, which traditionally require callback
> functions and manual marshalling of parameters.
>
> Creating and starting a coroutine is easy:
>
> coroutine = qemu_coroutine_create(my_coroutine);
> qemu_coroutine_enter(coroutine, my_data);
>
> The coroutine then executes until it returns or yields:
>
> void coroutine_fn my_coroutine(void *opaque) {
> MyData *my_data = opaque;
>
> /* do some work */
>
> qemu_coroutine_yield();
>
> /* do some more work */
> }
>
> Yielding switches control back to the caller of qemu_coroutine_enter().
> This is typically used to switch back to the main thread's event loop
> after issuing an asynchronous I/O request. The request callback will
> then invoke qemu_coroutine_enter() once more to switch back to the
> coroutine.
>
> Note that coroutines never execute concurrently and should only be used
> from threads which hold the global mutex. This restriction makes
> programming with coroutines easier than with threads. Race conditions
> cannot occur since only one coroutine may be active at any time. Other
> coroutines can only run across yield.
Mmh, is there anything that conceptually prevent fixing this limitation
later on? I would really like to remove such dependency long-term as
well to have VCPUs operate truly independently on independent device models.
Jan
--
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux
