Re: [PATCH V8 07/15] monitor: Update tracking iothread users with holder

[Markus Armbruster <armbru@redhat.com>]

Zhang Chen <zhangckid@gmail.com> writes:

> Based on monitor ID tracking iothread users with holder.
> Introduce the AioContext in the Monitor struct to avoid repeated calls to
> iothread_get_aio_context()

iothread_get_aio_context(iothread) returns iothread->ctx.  I doubt
avoiding the call is worth the complexity yet another variable adds.

>                            and ensure symmetrical ref/unref during
> monitor lifecycle.

What do you mean by that?

> Signed-off-by: Zhang Chen <zhangckid@gmail.com>
> ---
>  monitor/monitor-internal.h |  3 +++
>  monitor/monitor.c          | 20 ++++++++++++++++++--
>  monitor/qmp.c              |  3 ++-
>  3 files changed, 23 insertions(+), 3 deletions(-)
>
> diff --git a/monitor/monitor-internal.h b/monitor/monitor-internal.h
> index 2060311b03..92d7630921 100644
> --- a/monitor/monitor-internal.h
> +++ b/monitor/monitor-internal.h
> @@ -127,6 +127,9 @@ struct Monitor {
>      guint out_watch;
>      int mux_out;
>      int reset_seen;
> +
> +    /* iothread context */
> +    AioContext *ctx;
>  };
>  
>  struct MonitorHMP {
> diff --git a/monitor/monitor.c b/monitor/monitor.c
> index dafb4ad8b0..7eec6f967d 100644
> --- a/monitor/monitor.c
> +++ b/monitor/monitor.c
> @@ -529,7 +529,7 @@ int monitor_suspend(Monitor *mon)
>           * Kick I/O thread to make sure this takes effect.  It'll be
>           * evaluated again in prepare() of the watch object.
>           */
> -        aio_notify(iothread_get_aio_context(mon_iothread));
> +        aio_notify(mon->ctx);
>      }
>  
>      trace_monitor_suspend(mon, 1);
> @@ -564,7 +564,7 @@ void monitor_resume(Monitor *mon)
>          AioContext *ctx;
>  
>          if (mon->use_io_thread) {
> -            ctx = iothread_get_aio_context(mon_iothread);
> +            ctx = mon->ctx;
>          } else {
>              ctx = qemu_get_aio_context();
>          }
> @@ -612,6 +612,12 @@ void monitor_data_init(Monitor *mon, bool is_qmp, bool skip_flush,
>  {
>      if (use_io_thread && !mon_iothread) {
>          monitor_iothread_init();
> +
> +        IOThreadHolder holder = {
> +            .type = IO_THREAD_HOLDER_KIND_MONITOR_NAME,
> +            .u.monitor_name.monitor_name = (char *)mon->id,
> +        };
> +        mon->ctx = iothread_ref_and_get_aio_context(mon_iothread, &holder);
>      }
>      qemu_mutex_init(&mon->mon_lock);
>      mon->is_qmp = is_qmp;
> @@ -631,6 +637,16 @@ void monitor_data_destroy(Monitor *mon)
>      }
>      g_string_free(mon->outbuf, true);
>      qemu_mutex_destroy(&mon->mon_lock);
> +
> +    if (mon->ctx && mon_iothread) {
> +        IOThreadHolder holder = {
> +            .type = IO_THREAD_HOLDER_KIND_MONITOR_NAME,
> +            .u.monitor_name.monitor_name = (char *)mon->id,
> +        };
> +
> +        iothread_put_aio_context(mon_iothread, &holder);
> +        mon->ctx = NULL;
> +    }
>  }
>  
>  void monitor_cleanup(void)
> diff --git a/monitor/qmp.c b/monitor/qmp.c
> index b210850a15..b67674aef3 100644
> --- a/monitor/qmp.c
> +++ b/monitor/qmp.c
> @@ -565,7 +565,8 @@ void monitor_init_qmp(Chardev *chr, bool pretty, const char *id, Error **errp)
>           * since chardev might be running in the monitor I/O
>           * thread.  Schedule a bottom half.
>           */
> -        aio_bh_schedule_oneshot(iothread_get_aio_context(mon_iothread),
> +        Monitor *mon_p = &mon->common;
> +        aio_bh_schedule_oneshot(mon_p->ctx,
>                                  monitor_qmp_setup_handlers_bh, mon);
>          /* The bottom half will add @mon to @mon_list */
>      } else {

The patch does two things:

(1) Replace iothread_get_aio_context(mon_iothread) by mon->ctx.

(2) Call iothread_ref_and_get_aio_context() / iothread_put_aio_context().

I challenged (1).  If we decide we want it, I'll ask you to split the
patch.