Re: [Tarantool-patches] [PATCH v2 12/16] raft: move synchro queue clear to the worker fiber

[Serge Petrenko <sergepetrenko@tarantool.org>]

20.11.2020 02:46, Vladislav Shpilevoy пишет:
> The synchro queue was cleared from the Raft on_update trigger
> installed by box. It was fine as long as the trigger is called
> from the worker fiber, because it won't block the state machine,
> while the synchro queue clearance yields.
>
> But the trigger is going to be called from the Raft state machine
> directly soon. Because it will need to call
> box_update_ro_summary() right after Raft state is updated, without
> a yield to switch to the worker fiber. This will be done in scope
> of getting rid of box in the Raft library.
>
> It means, the trigger can't call box_clear_synchro_queue(). But it
> can schedule its execution for later, since the worker fiber now
> belongs to box. The patch does it.
>
> Part of #5303


Thanks for the patch! LGTM.

> ---
>   src/box/raft.c | 22 ++++++++++++++++++----
>   1 file changed, 18 insertions(+), 4 deletions(-)
>
> diff --git a/src/box/raft.c b/src/box/raft.c
> index 0027230da..5ccfb3449 100644
> --- a/src/box/raft.c
> +++ b/src/box/raft.c
> @@ -80,6 +80,19 @@ box_raft_request_to_msg(const struct raft_request *req, struct raft_msg *msg)
>   	};
>   }
>   
> +static void
> +box_raft_update_synchro_queue(struct raft *raft)
> +{
> +	assert(raft == box_raft());
> +	/*
> +	 * When the node became a leader, it means it will ignore all records
> +	 * from all the other nodes, and won't get late CONFIRM messages anyway.
> +	 * Can clear the queue without waiting for confirmations.
> +	 */
> +	if (raft->state == RAFT_STATE_LEADER)
> +		box_clear_synchro_queue(false);
> +}
> +
>   static int
>   box_raft_worker_f(va_list args)
>   {
> @@ -90,6 +103,7 @@ box_raft_worker_f(va_list args)
>   		box_raft_has_work = false;
>   
>   		raft_process_async(raft);
> +		box_raft_update_synchro_queue(raft);
>   
>   		if (!box_raft_has_work)
>   			fiber_yield();
> @@ -142,11 +156,11 @@ box_raft_on_update_f(struct trigger *trigger, void *event)
>   	if (raft->state != RAFT_STATE_LEADER)
>   		return 0;
>   	/*
> -	 * When the node became a leader, it means it will ignore all records
> -	 * from all the other nodes, and won't get late CONFIRM messages anyway.
> -	 * Can clear the queue without waiting for confirmations.
> +	 * If the node became a leader, time to clear the synchro queue. But it
> +	 * must be done in the worker fiber so as not to block the state
> +	 * machine, which called this trigger.
>   	 */
> -	box_clear_synchro_queue(false);
> +	box_raft_schedule_async(raft);
>   	return 0;
>   }
>   

-- 
Serge Petrenko