Future.cancel（）方法中的问题

Question

I have a below runnable task which is run by using ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(1, 1, 0L, TimeUnit.MILLISECONDS, new ArrayBlockingQueue<Runnable>(1)); This ensures that there will be only one waiting task in the queue.

protected void waitAndSweep(final String symbol) {
    try { 

        runnable = new Runnable() {
          @Override
          public void run() {
            try {
             // long sweepTime = symbolInfo.getSweepTime(symbol);
              // long timeSinceLastSweep = System.currentTimeMillis() - lastSliceSentTime;
              boolean sliceDone = Quant.equals(wave.getCommitedQuantity() % getSliceQuantity(),0);
              if(sliceDone){
                long timeSinceLastSliceQtySent = lastSliceSentTime == 0 ? getInterval() : System.currentTimeMillis() - lastSliceSentTime;
                long waitTime = timeSinceLastSliceQtySent >= getInterval() ? 0 : getInterval() - timeSinceLastSliceQtySent;
                logTradeEvent("waitAndSweep", symbol, "waittime: " + waitTime);
                if (waitTime > 0){
                  Thread.sleep(waitTime);
                }
              }

              callSweep(symbol);
            } catch(InterruptedException ie){
              ie.printStackTrace();
            }
            catch (Exception e) {
              logEvent(StrategyEntry.ERROR, "waitAndSweep", symbol,
                  "Exception caught...", e);
            }            
          }
        };

      self = threadPoolExecutor.submit(runnable);   
    }catch(RejectedExecutionException re){
      /* this exception will be thrown when wait and sweep is called more than twice.
       * threadPoolExecutor can have one running task and one waiting task.
       * */
      System.out.print(re);
      }catch (Exception e) {
      logEvent(StrategyEntry.ERROR, "waitAndSweep", symbol,
          "Exception caught...", e);
    }
  }

Consider the caller A :

private void callerA(){
waitandsweep();
waitandsweep();}

this craetes two task one will be running and another waiting in the queue.

Consider the callerB:

private void callerB(){
self.cancel(true);
waitandsweep();}

Expecting callerB to cancel all the tasks invoked by A. Actually it is not happening.. task invoked by caller B is getting rejected because already one task is waiting in the queue. Can you please tell why this behaviour happens?

edit 1 : How to cancel running task of executor?

Answer 1

The problem is, that Future.cancel(boolean) doesn't remove the task from the queue. The Task will not be executed, once it will be pulled by the Executor but until then its still in the queue

try to use threadPoolExecutor.purge(); right after cancel(); it will try to remove the canceled tasks

cancelling a running Task is not that easy, you could try following: call cancel(true); it will set Thread.interrupted() to true . Now in your Task check on some steps that value and so you can decide to skip next steps of your task