Re: [Qemu-devel] [PATCH v3] monitor: let cur_mon be per-thread

[Markus Armbruster]

Peter Xu <address@hidden> writes:

> In the future the monitor iothread may be accessing the cur_mon as
> well (via monitor_qmp_dispatch_one()).  Before we introduce a real
> Out-Of-Band command,

Uh, inhowfar are the commands marked allow-oob: true now not real?
These are migrate-recover, migrate-pause, x-oob-test.

Aside: having x-oob-test in QEMU proper is awful.  Is there really no
way around it?

>                      let's convert the cur_mon variable to be a
> per-thread variable to make sure there won't be a race between threads.
>
> Note that thread variables are not initialized to a valid value when new
> thread is created.  However for our case we don't need to set it up,
> since the cur_mon variable is only used in such a pattern:
>
>   old_mon = cur_mon;
>   cur_mon = xxx;
>   (do something, read cur_mon if necessary in the stack)
>   cur_mon = old_mon;
>
> It plays a role as stack variable, so no need to be initialized at all.
> We only need to make sure the variable won't be changed unexpectedly by
> other threads.

Do we plan to keep switching cur_mon forever?  Or do we intend to work
towards a 1:1 association between Monitor struct and monitor thread?

Even if we want the latter, I'm okay with this patch as an intermediate
step.

> Signed-off-by: Peter Xu <address@hidden>