[tarantool-patches] Re: [PATCH 1/4] Fix races related to object outdating

[Vladislav Shpilevoy]

Hi! Thanks for the patch! See 1 comment below and fixes on
the branch in a separate commit. Please, look and squash.

On 30/07/2018 11:56, AKhatskevich wrote:
> Reload/reconfigure may replace many of M fields during any yield.
> Old objects should not be accessed after they are outdated.
> 
> This commit handles such cases within `vshard.router`.
> ---
>   vshard/replicaset.lua   | 30 ++++++++++++++-----------
>   vshard/router/init.lua  | 58 +++++++++++++++++++++++++++++--------------------
>   vshard/storage/init.lua |  1 +
>   3 files changed, 52 insertions(+), 37 deletions(-)
> 
> diff --git a/vshard/router/init.lua b/vshard/router/init.lua
> index 142ddb6..1a0ed2f 100644
> --- a/vshard/router/init.lua
> +++ b/vshard/router/init.lua
> @@ -88,15 +94,18 @@ local function bucket_discovery(bucket_id)
>       log.verbose("Discovering bucket %d", bucket_id)
>       local last_err = nil
>       local unreachable_uuid = nil
> -    for uuid, replicaset in pairs(M.replicasets) do
> -        local _, err =
> -            replicaset:callrw('vshard.storage.bucket_stat', {bucket_id})
> -        if err == nil then
> -            bucket_set(bucket_id, replicaset)
> -            return replicaset
> -        elseif err.code ~= lerror.code.WRONG_BUCKET then
> -            last_err = err
> -            unreachable_uuid = uuid
> +    for uuid, _ in pairs(M.replicasets) do
> +        -- Handle reload/reconfigure.
> +        replicaset = M.replicasets[uuid]
> +        if replicaset then
> +            local _, err =
> +                replicaset:callrw('vshard.storage.bucket_stat', {bucket_id})
> +            if err == nil then
> +                return bucket_set(bucket_id, replicaset.uuid)

Do not return error immediately. You can continue iteration in the hope
of finding the bucket out on one of next replicasets. So here you
do 'if bucket_set ~= nil then return result end'. Else continue.

> +            elseif err.code ~= lerror.code.WRONG_BUCKET then
> +                last_err = err
> +                unreachable_uuid = uuid
> +            end
>           end
>       end
>       local err = nil