Am 07.08.2020 um 15:27 hat Markus Armbruster geschrieben:
> This is just a sketch. It's incomplete, needs comments and a real
> commit message.
>
> Support for "[PATCH v6 09/12] hmp: Add support for coroutine command
> handlers" is missing. Marked FIXME.
>
> As is, it goes on top of Kevin's series. It is meant to be squashed
> into PATCH 06, except for the FIXME, which needs to be resolved in PATCH
> 09 instead.
>
> Signed-off-by: Markus Armbruster <arm...@redhat.com>
> ---
> monitor/monitor.c | 35 +++++++++++++++--------------------
> 1 file changed, 15 insertions(+), 20 deletions(-)
>
> diff --git a/monitor/monitor.c b/monitor/monitor.c
> index 50fb5b20d3..8601340285 100644
> --- a/monitor/monitor.c
> +++ b/monitor/monitor.c
> @@ -82,38 +82,34 @@ bool qmp_dispatcher_co_shutdown;
> */
> bool qmp_dispatcher_co_busy;
>
> -/*
> - * Protects mon_list, monitor_qapi_event_state, coroutine_mon,
> - * monitor_destroyed.
> - */
> +/* Protects mon_list, monitor_qapi_event_state, * monitor_destroyed. */
> QemuMutex monitor_lock;
> static GHashTable *monitor_qapi_event_state;
> -static GHashTable *coroutine_mon; /* Maps Coroutine* to Monitor* */
>
> MonitorList mon_list;
> int mon_refcount;
> static bool monitor_destroyed;
>
> +static Monitor **monitor_curp(Coroutine *co)
> +{
> + static __thread Monitor *thread_local_mon;
> + static Monitor *qmp_dispatcher_co_mon;
> +
> + if (qemu_coroutine_self() == qmp_dispatcher_co) {
> + return &qmp_dispatcher_co_mon;
> + }
> + /* FIXME the coroutine hidden in handle_hmp_command() */
> + return &thread_local_mon;
> +}
Is thread_local_mon supposed to ever be set? The only callers of
monitor_set_cur() are the HMP and QMP dispatchers, which will return
something different.
So should we return NULL insetad of thread_local_mon...
> Monitor *monitor_cur(void)
> {
> - Monitor *mon;
> -
> - qemu_mutex_lock(&monitor_lock);
> - mon = g_hash_table_lookup(coroutine_mon, qemu_coroutine_self());
> - qemu_mutex_unlock(&monitor_lock);
> -
> - return mon;
> + return *monitor_curp(qemu_coroutine_self());
> }
...and return NULL here if monitor_curp() returned NULL...
> void monitor_set_cur(Coroutine *co, Monitor *mon)
> {
> - qemu_mutex_lock(&monitor_lock);
> - if (mon) {
> - g_hash_table_replace(coroutine_mon, co, mon);
> - } else {
> - g_hash_table_remove(coroutine_mon, co);
> - }
> - qemu_mutex_unlock(&monitor_lock);
> + *monitor_curp(co) = mon;
...and assert(monitor_curp(co) != NULL) here?
This approach looks workable, though the implementation of
monitor_curp() feels a bit brittle. The code is not significantly
simpler than the hash table based approach, but the assumptions it makes
are a bit more hidden.
Saving the locks is more a theoretical improvement because all callers
are slows paths anyway.
Kevin
