Create a task runner

[bromanko]

References

• Huey written in Python

Consuming Messages

Huey has some smart features added:

• Exponential backoff when the queue is empty
• Max delay between intervals when backing off
• Separating the consumer from the workers that perform task execution. This allows for multi-tasking.

I'm not going to implement multi-tasking right now. I can then treat this as a FIFO queue and worry less about ordering. Also, I can limit the amount of locking on the Sqlite database.

I will separate out consuming messages from working on them. Right now it seems a MailboxProcessor is a good option.

Workflow

type StopFlag = 
  | None
  | Shutdown

type Consumer(timeoutMs = 1000) =
  let worker = MailboxProcessor()
  let mutable stopFlag = None

  member rec _.Loop() =
    if sopFlag = Shutdown then 
      shutdown
      ()
    else
      try
        dequeTask
        |> worker.exec
      with ex -> log ex

      Thread.sleep time
      this.Loop()

let private handleSignals consumer = 
  // hook up the signals to stop the consumer
  if SIGIT
    consumer.Shutdown()
  ()

let main argv = 
  let consumer = new Consumer()
  handleSignals consumer
  consumer.Loop()

  0

Exception Handling

Exceptions should not terminate the process. Rather, they should cause any current task to still be in the queue. At some point I'll need to add dead-letter handling.