Lua script analysis of Laravel delay queue implementation

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Laravel implements Redis delay Lua scripts are used in queues to ensure the atomicity of operations between different queues
In Laravel5.1, four Lua script methods are mainly used to ensure the atomicity of different queue operations

1. Count the number of queue tasks Method

1.llen counts the number of list queues

2.zcard counts the amount of zset queue data

/**
 * 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 <<<&#39;LUA&#39;
         return redis.call(&#39;llen&#39;, KEYS[1]) + redis.call(&#39;zcard&#39;, KEYS[2]) +
         redis.call(&#39;zcard&#39;, KEYS[3])
    LUA;
}

2. Put the pop queue task into the reserved queue

/**
 * 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 <<<&#39;LUA&#39;
      -- Pop the first job off of the queue...
     local job = redis.call(&#39;lpop&#39;, 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[&#39;attempts&#39;] = reserved[&#39;attempts&#39;] + 1
        reserved = cjson.encode(reserved)
        redis.call(&#39;zadd&#39;, KEYS[2], ARGV[1], reserved)
     end
    return {job, reserved}
  LUA;
}

3. Add the tasks from the reserved queue to the delayed queue

/**
 * 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 <<<&#39;LUA&#39;
       -- Remove the job from the current queue...
       redis.call(&#39;zrem&#39;, KEYS[2], ARGV[1])
       -- Add the job onto the "delayed" queue...
       redis.call(&#39;zadd&#39;, KEYS[1], ARGV[2], ARGV[1])
       return true
    LUA;
}

4. Merge the tasks that meet the reserved queue time into the execution queue

    /**
     * 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 <<<&#39;LUA&#39;
        -- Get all of the jobs with an expired "score"...
           local val = redis.call(&#39;zrangebyscore&#39;, KEYS[1], &#39;-inf&#39;, 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(&#39;zremrangebyrank&#39;, KEYS[1], 0, #val - 1)

             for i = 1, #val, 100 do
               redis.call(&#39;rpush&#39;, KEYS[2], unpack(val, i, math.min(i+99, #val)))
             end
           end
          return val
        LUA;
}

                           

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