Re: [Qemu-devel] [PATCH] qemu-iothread: IOThread supports the GMainContext event loop

[Paolo Bonzini <pbonzini@redhat.com>]

----- Original Message -----
> From: "Wang yong" <wang.yong155@zte.com.cn>
> To: pbonzini@redhat.com, stefanha@redhat.com, famz@redhat.com, jasowang@redhat.com
> Cc: "wang yong155" <wang.yong155@zte.com.cn>, "wang guang55" <wang.guang55@zte.com.cn>, "zhangchen fnst"
> <zhangchen.fnst@cn.fujitsu.com>, "zhang zhanghailiang" <zhang.zhanghailiang@huawei.com>, lizhijian@cn.fujitsu.com,
> qemu-devel@nongnu.org
> Sent: Friday, August 11, 2017 2:29:15 AM
> Subject: [PATCH] qemu-iothread: IOThread supports the GMainContext event loop
> 
> From: Wang Yong<wang.yong155@zte.com.cn>
> 
> IOThread uses AioContext event loop and does not run a GMainContext.
> Therefore,chardev cannot work in IOThread,such as the chardev is
> used for colo-compare packets reception.
> 
> This patch makes the IOThread run the GMainContext event loop,
> chardev and IOThread can work together.
> 
> Signed-off-by: Wang Yong<wang.yong155@zte.com.cn>
> Signed-off-by: Wang Guang<wang.guang55@zte.com.cn>

Nice.  Just a note, I think an iothread should have its own (optional)
GMainContext accessed with iothread_get_g_main_context(iothread).  When
you call it for the first time, the iothread:

1) creates a GMainContext

2) adds the AioContext as a GSource in the GMainContext

3) asks iothread_run to switch from the AioContext loop to the
GMainContext loop


To simplify thread-safety:

1) the GMainContext can be wrapped with a GOnce

2) the GOnce callback can leave steps 2 and 3 to a bottom half.

Paolo

> ---
>  include/sysemu/iothread.h |  1 +
>  iothread.c                | 13 +++++++++++++
>  2 files changed, 14 insertions(+)
> 
> diff --git a/include/sysemu/iothread.h b/include/sysemu/iothread.h
> index e6da1a4..ffe4e8a 100644
> --- a/include/sysemu/iothread.h
> +++ b/include/sysemu/iothread.h
> @@ -24,6 +24,7 @@ typedef struct {
>  
>      QemuThread thread;
>      AioContext *ctx;
> +    GMainLoop *loop;
>      QemuMutex init_done_lock;
>      QemuCond init_done_cond;    /* is thread initialization done? */
>      bool stopping;
> diff --git a/iothread.c b/iothread.c
> index beeb870..b6f3c3c 100644
> --- a/iothread.c
> +++ b/iothread.c
> @@ -46,6 +46,7 @@ AioContext *qemu_get_current_aio_context(void)
>  static void *iothread_run(void *opaque)
>  {
>      IOThread *iothread = opaque;
> +    GMainContext *context;
>  
>      rcu_register_thread();
>  
> @@ -57,6 +58,15 @@ static void *iothread_run(void *opaque)
>  
>      while (!atomic_read(&iothread->stopping)) {
>          aio_poll(iothread->ctx, true);
> +
> +        context = iothread->ctx->source.context;
> +        if (context) {
> +            iothread->loop = g_main_loop_new(context, TRUE);
> +            g_main_loop_run(iothread->loop);
> +
> +            g_main_loop_unref(iothread->loop);
> +            g_main_context_unref(context);
> +        }
>      }
>  
>      rcu_unregister_thread();
> @@ -72,6 +82,9 @@ static int iothread_stop(Object *object, void *opaque)
>          return 0;
>      }
>      iothread->stopping = true;
> +    if (iothread->loop) {
> +        g_main_loop_quit(iothread->loop);
> +    }
>      aio_notify(iothread->ctx);
>      qemu_thread_join(&iothread->thread);
>      return 0;
> --
> 1.8.3.1
> 
> 
>