73 lines
1.5 KiB
Ruby
73 lines
1.5 KiB
Ruby
# frozen_string_literal: true
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class DistributedMemoizer
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# never wait for longer that 1 second for a cross process lock
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MAX_WAIT = 2
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LOCK = Mutex.new
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# memoize a key across processes and machines
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def self.memoize(key, duration = 60 * 60 * 24, redis = nil)
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redis ||= Discourse.redis
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redis_key = self.redis_key(key)
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unless result = redis.get(redis_key)
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redis_lock_key = self.redis_lock_key(key)
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start = Time.now
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got_lock = false
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begin
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while Time.now < start + MAX_WAIT && !got_lock
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LOCK.synchronize do
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got_lock = get_lock(redis, redis_lock_key)
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end
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sleep 0.001
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end
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unless result = redis.get(redis_key)
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result = yield
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redis.setex(redis_key, duration, result)
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end
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ensure
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# NOTE: delete regardless so next one in does not need to wait MAX_WAIT again
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redis.del(redis_lock_key)
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end
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end
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result
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end
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def self.redis_lock_key(key)
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+"memoize_lock_" << key
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end
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def self.redis_key(key)
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+"memoize_" << key
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end
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# Used for testing
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def self.flush!
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Discourse.redis.scan_each(match: "memoize_*").each { |key| Discourse.redis.del(key) }
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end
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protected
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def self.get_lock(redis, redis_lock_key)
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redis.watch(redis_lock_key)
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current = redis.get(redis_lock_key)
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return false if current
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unique = SecureRandom.hex
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result = redis.multi do
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redis.setex(redis_lock_key, MAX_WAIT, unique)
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end
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redis.unwatch
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result == ["OK"]
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end
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end
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