discourse/lib/distributed_mutex.rb

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# Cross-process locking using Redis.
class DistributedMutex
attr_accessor :redis
attr_reader :got_lock
def initialize(key, redis=nil)
@key = key
@redis = redis || $redis
@got_lock = false
end
def try_to_get_lock
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
end
def get_lock
return if @got_lock
start = Time.now
while !@got_lock
try_to_get_lock
end
end
def release_lock
redis.del @key
@got_lock = false
end
def synchronize
get_lock
yield
ensure
release_lock
end
end