Question

Is there a better way to do this? I would rather use an existing framework from j.u.c instead of rolling my own….

Please look at the “run” method.

I need to resubmit the Callable as soon as a result is obtained from the Future.
I’m using this separate Runnable Thread, just to do exactly this, as shown below.

Though this should compile, its obviously not a working piece of code..

public class ResubmitOnCompletion implements Runnable {

    private CompletionService<DeviceData> completionService;

    private ConcurrentHashMap<String, Device> devices;

    public void run() {

      //-- keep resubmitting the callable.
      while(true){


        try {
          //-- Get the returned data from completed job
          Future<DeviceData> f=null;
          DeviceData dd=null;

          f = completionService.take();

          //-- Get the completed job's data 
          dd=f.get();

          //-- now resubmit the job if device still is part of the active device collection
          completionService.submit((Callable<DeviceData>) devices.get(dd.getDeviceId()));
      }
      catch (CancellationException e) {
        e.printStackTrace();
      }
      catch (InterruptedException e) {
        e.printStackTrace();
      } catch (ExecutionException e) {
        e.printStackTrace();
      }         
    }   
  }


    //-- Device Data
    private class DeviceData {
      /**
       * Unique Device Identifier
       */
      private final String deviceId;

      /**
       * Holds all numeric data of the device.
       * Key=Variable id of the parameter
       * Value=Numeric value of the parameter
       */
      private final ConcurrentHashMap<String, BigDecimal> numericData;



      private DeviceData(String deviceId,
          ConcurrentHashMap<String, BigDecimal> numericData) {
        super();
        this.deviceId = deviceId;
        this.numericData = numericData;
      }


      /**
       * @return the deviceId
       */
      public String getDeviceId() {
        return deviceId;
      }

      /**
       * @return the numericData
       */
      public ConcurrentHashMap<String, BigDecimal> getNumericData() {
        return numericData;
      }
    }   

    //-- Device
    private class Device {
      public DeviceData call() throws Exception {
        return new DeviceData("",new ConcurrentHashMap<String, BigDecimal>());
      }

    }
}

Answer 1

You can simply submit the Runnable and within the run re submit itself

ExecutorService e = Executors.newFixedThreadPool(1);

private void submitWork(){
   e.submit(new Runnable(){
       public void run(){
          ///do work with devices and get its data            
          e.submit(this);
       }
   });
}

I am unsure why this would not work.