73 lines
2.1 KiB
Ruby
73 lines
2.1 KiB
Ruby
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require 'digest/md5'
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require 'redis'
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class UncomplicatedMutex
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attr_reader :lock_name
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MutexTimeout = Class.new(StandardError)
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LUA_ACQUIRE = "return redis.call('SET', KEYS[1], ARGV[2], 'NX', 'EX', ARGV[1]) and redis.call('expire', KEYS[1], ARGV[1]) and 1 or 0"
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LUA_RELEASE = "if redis.call('get', KEYS[1]) == ARGV[1] then return redis.call('del', KEYS[1]) else return 0 end"
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def initialize(obj, opts = {})
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@verbose = opts[:verbose]
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@timeout = opts[:timeout] || 300
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@fail_on_timeout = opts[:fail_on_timeout]
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@ticks = opts[:ticks] || 100
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@wait_tick = @timeout.to_f / @ticks.to_f
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@redis = opts[:redis] || Redis.new
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@lock_name = "lock:#{obj.class.name}:#{obj.id}".squeeze(":")
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@token = Digest::MD5.new.hexdigest("#{@lock_name}_#{Time.now.to_f}")
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end
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def acquire_mutex
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puts("Running transaction to acquire the lock #{@lock_name}") if @verbose
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@redis.eval(LUA_ACQUIRE, [ @lock_name ], [ @timeout, @token ]) == 1
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end
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def destroy_mutex
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puts("Destroying the lock #{@lock_name}") if @verbose
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@redis.del(@lock_name)
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end
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def lock(&block)
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begin
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wait_for_mutex
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yield block
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ensure
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release_mutex
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end
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end
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def overwrite_mutex
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puts("Replacing the lock #{@lock_name} with #{@token}") if @verbose
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@redis.set(@lock_name, @token)
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end
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def recurse_until_ready(depth = 1)
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return false if depth == @ticks
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wait_a_tick if depth > 1
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acquire_mutex || recurse_until_ready(depth + 1)
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end
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def release_mutex
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puts("Releasing the lock #{@lock_name} if it still holds the value '#{@token}'") if @verbose
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@redis.eval(LUA_RELEASE, [ @lock_name ], [ @token ])
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end
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def wait_a_tick
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puts("Sleeping #{@wait_tick} for the lock #{@lock_name} to become available") if @verbose
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sleep(@wait_tick)
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end
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def wait_for_mutex
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if recurse_until_ready
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puts("Acquired lock #{@lock_name}") if @verbose
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else
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puts("Failed to acquire the lock") if @verbose
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raise MutexTimeout.new("Failed to acquire the lock") if @fail_on_timeout
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overwrite_mutex
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end
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end
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end
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