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30990006a9
This reduces chances of errors where consumers of strings mutate inputs and reduces memory usage of the app. Test suite passes now, but there may be some stuff left, so we will run a few sites on a branch prior to merging
76 lines
1.4 KiB
Ruby
76 lines
1.4 KiB
Ruby
# frozen_string_literal: true
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# Cross-process locking using Redis.
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class DistributedMutex
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DEFAULT_VALIDITY ||= 60
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def self.synchronize(key, redis: nil, validity: DEFAULT_VALIDITY, &blk)
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self.new(
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key,
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redis: redis,
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validity: validity
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).synchronize(&blk)
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end
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def initialize(key, redis: nil, validity: DEFAULT_VALIDITY)
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@key = key
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@using_global_redis = true if !redis
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@redis = redis || $redis
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@mutex = Mutex.new
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@validity = validity
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end
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CHECK_READONLY_ATTEMPT ||= 10
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# NOTE wrapped in mutex to maintain its semantics
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def synchronize
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@mutex.lock
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attempts = 0
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while !try_to_get_lock
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sleep 0.001
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# in readonly we will never be able to get a lock
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if @using_global_redis && Discourse.recently_readonly?
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attempts += 1
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if attempts > CHECK_READONLY_ATTEMPT
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raise Discourse::ReadOnly
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end
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end
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end
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yield
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ensure
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@redis.del @key
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@mutex.unlock
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end
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private
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def try_to_get_lock
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got_lock = false
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if @redis.setnx @key, Time.now.to_i + @validity
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@redis.expire @key, @validity
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got_lock = true
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else
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begin
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@redis.watch @key
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time = @redis.get @key
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if time && time.to_i < Time.now.to_i
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got_lock = @redis.multi do
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@redis.set @key, Time.now.to_i + @validity
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end
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end
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ensure
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@redis.unwatch
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end
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end
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got_lock
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end
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end
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