discourse/lib/distributed_mutex.rb

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# Cross-process locking using Redis.
class DistributedMutex
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def self.synchronize(key, redis = nil, &blk)
self.new(key, redis).synchronize(&blk)
end
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def initialize(key, redis = nil)
@key = key
@redis = redis || $redis
@mutex = Mutex.new
end
# NOTE wrapped in mutex to maintain its semantics
def synchronize
@mutex.lock
while !try_to_get_lock
sleep 0.001
end
yield
ensure
@redis.del @key
@mutex.unlock
end
private
def try_to_get_lock
got_lock = false
if @redis.setnx @key, Time.now.to_i + 60
@redis.expire @key, 60
got_lock = true
else
begin
@redis.watch @key
time = @redis.get @key
if time && time.to_i < Time.now.to_i
got_lock = @redis.multi do
@redis.set @key, Time.now.to_i + 60
end
end
ensure
@redis.unwatch
end
end
got_lock
end
end