Re: [PATCH] block/aio_task: allow start/wait task from any coroutine

["Denis V. Lunev" <den@openvz.org>]

On 6/11/20 10:36 AM, Vladimir Sementsov-Ogievskiy wrote:
> Currently, aio task pool assumes that there is a main coroutine, which
> creates tasks and wait for them. Let's remove the restriction by using
> CoQueue. Code becomes clearer, interface more obvious.
>
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
>
> Hi! Here is my counter-propasal for
> "[PATCH 1/2] aio: allow to wait for coroutine pool from different coroutine"
> by Denis. I'm sure that if we are going to change something here, better
> is make the interface work from any coroutine without the restriction of
> only-on-waiter at the moment.
>
> (Note, that it is still not thread-safe)
>
>
>  block/aio_task.c | 15 ++++-----------
>  1 file changed, 4 insertions(+), 11 deletions(-)
>
> diff --git a/block/aio_task.c b/block/aio_task.c
> index 88989fa248..d48b29ff83 100644
> --- a/block/aio_task.c
> +++ b/block/aio_task.c
> @@ -27,11 +27,10 @@
>  #include "block/aio_task.h"
>  
>  struct AioTaskPool {
> -    Coroutine *main_co;
>      int status;
>      int max_busy_tasks;
>      int busy_tasks;
> -    bool waiting;
> +    CoQueue waiters;
>  };
>  
>  static void coroutine_fn aio_task_co(void *opaque)
> @@ -52,21 +51,15 @@ static void coroutine_fn aio_task_co(void *opaque)
>  
>      g_free(task);
>  
> -    if (pool->waiting) {
> -        pool->waiting = false;
> -        aio_co_wake(pool->main_co);
> -    }
> +    qemu_co_queue_next(&pool->waiters);
nope, this will wakeup only single waiter.
the code will deadlock If there are 2 waiters for the last
entry.

You need something like qemu_co_queue_restart_all() here
at least.

Den