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 Sat, 15 Aug 2020 18:04:33 +0300 (MSK)
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 <20200814211442.667099-6-gorcunov@gmail.com>
From: Vladislav Shpilevoy <v.shpilevoy@tarantool.org>
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Date: Sat, 15 Aug 2020 17:04:32 +0200
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Subject: Re: [Tarantool-patches] [PATCH v7 5/8] applier: factor out latch
	locking
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To: Cyrill Gorcunov <gorcunov@gmail.com>, tml <tarantool-patches@dev.tarantool.org>

Thanks for the patch!

On 14.08.2020 23:14, Cyrill Gorcunov wrote:
> We will need to reuse this helpers.
> 
> Part-of #5129
> 
> Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
> ---
>  src/box/applier.cc | 43 +++++++++++++++++++++++++++++--------------
>  1 file changed, 29 insertions(+), 14 deletions(-)
> 
> diff --git a/src/box/applier.cc b/src/box/applier.cc
> index 98fb87375..60689f6d3 100644
> --- a/src/box/applier.cc
> +++ b/src/box/applier.cc
> @@ -799,6 +799,29 @@ applier_txn_wal_write_cb(struct trigger *trigger, void *event)
>  	return 0;
>  }
>  
> +/*
> + * In a full mesh topology, the same set of changes
> + * may arrive via two concurrently running appliers.
> + * Hence we need a latch to strictly order all changes
> + * that belong to the same server id.
> + */
> +static inline struct latch *
> +applier_lock(uint32_t replica_id)
> +{
> +	struct replica *replica = replica_by_id(replica_id);
> +	struct latch *latch = (replica ? &replica->order_latch :

We usually use != NULL to check if a pointer is not NULL. To emphasize
it is not a boolean variable in the code.

> +			       &replicaset.applier.order_latch);
> +	latch_lock(latch);
> +	return latch;
> +}