Laravel延迟队列实现之Lua脚本解析

摘要：在实现延迟队列时使用了脚本保证不同队列间操作的原子性在中主要是通过个脚本方法保证不同队列操作的原子性的一统计队列任务数量方法统计队列数量统计队列数据量二队列任务放入保留队列三将任务由添加队列到队列中四将队

Laravel在实现Redis延迟队列时使用了Lua脚本保证不同队列间操作的原子性
在Laravel5.1中主要是通过4个Lua脚本方法保证不同队列操作的原子性的

一、统计队列任务数量方法

1.llen 统计list队列数量

2.zcard统计zset队列数据量

    /**
     * Get the Lua script for computing the size of queue.
     *
     * KEYS[1] - The name of the primary queue
     * KEYS[2] - The name of the "delayed" queue
     * KEYS[3] - The name of the "reserved" queue
     *
     * @return string
     */
    public static function size()
    {
        return <<<"LUA"
             return redis.call("llen", KEYS[1]) + redis.call("zcard", KEYS[2]) + 
             redis.call("zcard", KEYS[3])
        LUA;
    }

二、pop队列任务放入reserved（保留）队列

    /**
     * Get the Lua script for popping the next job off of the queue.
     *
     * KEYS[1] - The queue to pop jobs from, for example: queues:foo
     * KEYS[2] - The queue to place reserved jobs on, for example: queues:foo:reserved
     * ARGV[1] - The time at which the reserved job will expire
     *
     * @return string
     */
    public static function pop()
    {
      return <<<"LUA"
          -- Pop the first job off of the queue...
         local job = redis.call("lpop", KEYS[1])
         local reserved = false

         if(job ~= false) then
            -- Increment the attempt count and place job on the reserved queue...
            reserved = cjson.decode(job)
            reserved["attempts"] = reserved["attempts"] + 1
            reserved = cjson.encode(reserved)
            redis.call("zadd", KEYS[2], ARGV[1], reserved)
         end
        return {job, reserved}
      LUA;
    }

三、将任务由添加reserved队列到delayed队列中

    /**
     * Get the Lua script for releasing reserved jobs.
     *
     * KEYS[1] - The "delayed" queue we release jobs onto, for example: queues:foo:delayed
     * KEYS[2] - The queue the jobs are currently on, for example: queues:foo:reserved
     * ARGV[1] - The raw payload of the job to add to the "delayed" queue
     * ARGV[2] - The UNIX timestamp at which the job should become available
     *
     * @return string
     */
    public static function release()
    {
        return <<<"LUA"
           -- Remove the job from the current queue...
           redis.call("zrem", KEYS[2], ARGV[1])
           -- Add the job onto the "delayed" queue...
           redis.call("zadd", KEYS[1], ARGV[2], ARGV[1])
           return true
        LUA;
    }

四、将reserved队列满足时间的任务合并到执行队列中

    /**
     * Get the Lua script to migrate expired jobs back onto the queue.
     *
     * KEYS[1] - The queue we are removing jobs from, for example: queues:foo:reserved
     * KEYS[2] - The queue we are moving jobs to, for example: queues:foo
     * ARGV[1] - The current UNIX timestamp
     *
     * @return string
     */
    public static function migrateExpiredJobs()
    {
        return <<<"LUA"
        -- Get all of the jobs with an expired "score"...
           local val = redis.call("zrangebyscore", KEYS[1], "-inf", ARGV[1])

        -- If we have values in the array, we will remove them from the first queue
        -- and add them onto the destination queue in chunks of 100, which moves
        -- all of the appropriate jobs onto the destination queue very safely.
           if(next(val) ~= nil) then
             redis.call("zremrangebyrank", KEYS[1], 0, #val - 1)

             for i = 1, #val, 100 do
               redis.call("rpush", KEYS[2], unpack(val, i, math.min(i+99, #val)))
             end
           end
          return val
        LUA;
    }