discourse/lib/distributed_memoizer.rb

60 lines
1.2 KiB
Ruby

class DistributedMemoizer
# never wait for longer that 1 second for a cross process lock
MAX_WAIT = 2
LOCK = Mutex.new
# memoize a key across processes and machines
def self.memoize(key, duration = 60 * 60 * 24, redis = nil)
redis ||= $redis
redis_key = self.redis_key(key)
unless result = redis.get(redis_key)
redis_lock_key = self.redis_lock_key(key)
start = Time.new
got_lock = false
while Time.new < start + MAX_WAIT && !got_lock
LOCK.synchronize do
got_lock = get_lock(redis,redis_lock_key)
end
sleep 0.001
end
unless result = redis.get(redis_key)
result = yield
redis.setex(redis_key, duration, result)
end
redis.del(redis_lock_key)
end
result
end
def self.redis_lock_key(key)
"memoize_lock_" << key
end
def self.redis_key(key)
"memoize_" << key
end
protected
def self.get_lock(redis, redis_lock_key)
redis.watch(redis_lock_key)
current = redis.get(redis_lock_key)
return false if current
unique = SecureRandom.hex
result = redis.multi do
redis.setex(redis_lock_key, MAX_WAIT, unique)
end
redis.unwatch
return result == ["OK"]
end
end