Go DelayedQueue

Delayed queue with Redis implementation

ref: https://redislabs.com/ebook/part-2-core-concepts/chapter-6-application-components-in-redis/6-4-task-queues/6-4-2-delayed-tasks/

Basic concept:

1. User redis sorted set as the delayed queue
2. When enqueuing data to the delayed queue, we use execution timestamp as the score, e.g. use 1620199248 as the score (ZSet)
3. When de-queuing data, we use ZRangeByScore and ZRem with current timestamp to check if there is data.
4. When there is nothing in the queue, sleep for a period.

Workflow Chart:
+----------+           +--------------+                   +--------------+
|          |           |              |                   |              |
|  Caller  |           | DelayedQueue |                   | WorkerQueue  |
|          |           | Consumer     +----------------+  | Consumers    |
|          |           |              |                |  |              |
+----+-----+           +---+-^--------+                |  +-----+-^------+
     |                     | |                         |        | |
     |1.Add jobs with      | |2.Consume and add jobs   |        | |3.Consume and process the jobs
     | a delayed time      | | to working queue        |        | |
     |                     | |                         |        | |
+----v---------------------v-+-----------------------+ |  +-----v-+-----------------------------------+
|                                                    | |  |                                           |
|  DelayedQueue(Redis Sorted Set)                    | +-->  WorkingQueue(Redis List)[work_q]         |
| +-----------+------------------------------------+ |    | +------------------------------------+    |
| | score     | member                             | |    | | member                             |    |
| |(timestamp)|[queueName,funcName,{"arg1":"1"}]   | |    | |[queueName,funcName,{"arg1":"1"}]   |    |
| +-----------+------------------------------------+ |    | +------------------------------------+    |
| |1620299103 |["work_q","CallAPI","{"arg1":"1"}"] | |    | |["work_q","CallAPI","{"arg1":"1"}"] |    |
| +-----------+------------------------------------+ |    | +------------------------------------+    |
| |1620100100 | ...                                | |    | | ...                                |    |
| +-----------+------------------------------------+ |    | +------------------------------------+    |
|                                                    |    |                                           |
+----------------------------------------------------+    +-------------------------------------------+

Chart created by: https://asciiflow.com/

Example is in example folder.