144 lines
4.3 KiB
Ruby
144 lines
4.3 KiB
Ruby
# frozen_string_literal: true
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require 'securerandom'
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module Gitlab
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# This class implements an 'exclusive lease'. We call it a 'lease'
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# because it has a set expiry time. We call it 'exclusive' because only
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# one caller may obtain a lease for a given key at a time. The
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# implementation is intended to work across GitLab processes and across
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# servers. It is a cheap alternative to using SQL queries and updates:
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# you do not need to change the SQL schema to start using
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# ExclusiveLease.
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#
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class ExclusiveLease
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PREFIX = 'gitlab:exclusive_lease'
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NoKey = Class.new(ArgumentError)
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LUA_CANCEL_SCRIPT = <<~EOS
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local key, uuid = KEYS[1], ARGV[1]
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if redis.call("get", key) == uuid then
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redis.call("del", key)
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end
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EOS
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LUA_RENEW_SCRIPT = <<~EOS
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local key, uuid, ttl = KEYS[1], ARGV[1], ARGV[2]
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if redis.call("get", key) == uuid then
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redis.call("expire", key, ttl)
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return uuid
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end
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EOS
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def self.get_uuid(key)
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Gitlab::Redis::SharedState.with do |redis|
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redis.get(redis_shared_state_key(key)) || false
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end
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end
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# yield to the {block} at most {count} times per {period}
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#
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# Defaults to once per hour.
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#
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# For example:
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#
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# # toot the train horn at most every 20min:
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# throttle(locomotive.id, count: 3, period: 1.hour) { toot_train_horn }
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# # Brake suddenly at most once every minute:
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# throttle(locomotive.id, period: 1.minute) { brake_suddenly }
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# # Specify a uniqueness group:
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# throttle(locomotive.id, group: :locomotive_brake) { brake_suddenly }
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#
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# If a group is not specified, each block will get a separate group to itself.
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def self.throttle(key, group: nil, period: 1.hour, count: 1, &block)
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group ||= block.source_location.join(':')
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return if new("el:throttle:#{group}:#{key}", timeout: period.to_i / count).waiting?
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yield
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end
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def self.cancel(key, uuid)
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return unless key.present?
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Gitlab::Redis::SharedState.with do |redis|
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redis.eval(LUA_CANCEL_SCRIPT, keys: [ensure_prefixed_key(key)], argv: [uuid])
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end
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end
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def self.redis_shared_state_key(key)
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"#{PREFIX}:#{key}"
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end
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def self.ensure_prefixed_key(key)
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raise NoKey unless key.present?
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key.start_with?(PREFIX) ? key : redis_shared_state_key(key)
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end
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# Removes any existing exclusive_lease from redis
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# Don't run this in a live system without making sure no one is using the leases
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def self.reset_all!(scope = '*')
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Gitlab::Redis::SharedState.with do |redis|
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redis.scan_each(match: redis_shared_state_key(scope)).each do |key|
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redis.del(key)
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end
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end
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end
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def initialize(key, uuid: nil, timeout:)
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@redis_shared_state_key = self.class.redis_shared_state_key(key)
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@timeout = timeout
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@uuid = uuid || SecureRandom.uuid
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end
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# Try to obtain the lease. Return lease UUID on success,
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# false if the lease is already taken.
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def try_obtain
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# Performing a single SET is atomic
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Gitlab::Redis::SharedState.with do |redis|
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redis.set(@redis_shared_state_key, @uuid, nx: true, ex: @timeout) && @uuid
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end
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end
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# This lease is waiting to obtain
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def waiting?
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!try_obtain
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end
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# Try to renew an existing lease. Return lease UUID on success,
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# false if the lease is taken by a different UUID or inexistent.
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def renew
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Gitlab::Redis::SharedState.with do |redis|
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result = redis.eval(LUA_RENEW_SCRIPT, keys: [@redis_shared_state_key], argv: [@uuid, @timeout])
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result == @uuid
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end
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end
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# Returns true if the key for this lease is set.
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def exists?
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Gitlab::Redis::SharedState.with do |redis|
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redis.exists?(@redis_shared_state_key) # rubocop:disable CodeReuse/ActiveRecord
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end
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end
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# Returns the TTL of the Redis key.
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#
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# This method will return `nil` if no TTL could be obtained.
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def ttl
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Gitlab::Redis::SharedState.with do |redis|
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ttl = redis.ttl(@redis_shared_state_key)
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ttl if ttl > 0
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end
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end
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# Gives up this lease, allowing it to be obtained by others.
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def cancel
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self.class.cancel(@redis_shared_state_key, @uuid)
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end
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end
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end
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Gitlab::ExclusiveLease.prepend_mod_with('Gitlab::ExclusiveLease')
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