Package limn.concurrent

Interface Job

public interface Job
A started piece of background work, as seen by whoever asked for it. Held so that the request can be withdrawn: a field on the widget that started it, cancelled when the widget starts the next one or is taken off screen.

All three methods are safe to call from any thread; cancel() guarantees more when it is called on the UI thread.

  • Method Summary

    Modifier and Type
    Method
    Description
    void
    cancel()
    Withdraws the request.
    boolean
    isCancelled()
     
    boolean
    isDone()
     

  • Method Details

    • cancel

      void cancel()
      Withdraws the request. Returns immediately, and the body is never interrupted.

      Cancel on the UI thread. That is the precondition on the guarantee worth having: called there, no success, failure or progress callback runs after this returns. Called from any other thread it promises less: a delivery may already be executing on the UI thread when the flag is set, and that one finishes. Nothing is delivered after the flag is seen either way, and the reason to cancel (a view closing, the next keystroke) arrives on the UI thread anyway.

      What holds from any thread: the body does not run at all if the worker pool has not picked it up yet. What does not: that a body already running stops. It keeps going until it returns or notices Progress.isCancelled(), holding a worker thread until then (so cancelling ten jobs gives back no threads), and whatever it produces is discarded rather than delivered.

      Calling this more than once, or after the work has finished, is a no-op.

    • isCancelled

      boolean isCancelled()
      Returns:
      true once cancel() has been called

    • isDone

      boolean isDone()
      Returns:
      true once the body has returned or thrown, or once it has been skipped because the job was cancelled before the pool reached it. It says nothing about whether a callback ran: this flips on the worker thread the instant the body returns, and the delivery it triggers runs on a later frame, so polling this and then reading what a success handler was to set is a race. Do that work in the handler. A cancelled job is done and delivers nothing.