并发执行Java 8

Question

I am new to concurrent programming with java and trying to start some Callables asynchronously. But the code seems to block my programm flow, where the Callables are given to the executorService es.invokeAll(tasks) :

public void checkSensorConnections(boolean fireEvent) {
    List<Callable<Void>> tasks = new ArrayList<>();

    getSensors().forEach(sensor -> {
        tasks.add(writerService.openWriteConnection(sensor));
        tasks.add(readerService.openReadConnection(sensor));
    });

    try {
        LOG.info("Submmitting tasks");

        ExecutorService es = Executors.newWorkStealingPool();
        es.invokeAll(tasks);

        LOG.info("Tasks submitted");
    } catch (InterruptedException e) {
        LOG.error("could not open sensor-connections", e);
        error(MeasurmentScrewMinerError.OPEN_CONNECTION_ERROR);
    }
}

I have some log statements controlling the flow of the program. As you can see is that the execution waits until the two tasks are executed.

2017-01-19 16:06:06,474 INFO [main] de.cgh.screwminer.service.measurement.MeasurementService (MeasurementService.java:127) - Submmitting tasks

2017-01-19 16:06:08,477 ERROR [pool-2-thread-2] de.cgh.screwminer.service.measurement.SensorReadService (SensorReadService.java:68) - sensor Drehmoment read-connection could not be opened java.net.SocketTimeoutException: Receive timed out ...

2017-01-19 16:06:08,477 ERROR [pool-2-thread-4] de.cgh.screwminer.service.measurement.SensorReadService (SensorReadService.java:68) - sensor Kraft read-connection could not be opened java.net.SocketTimeoutException: Receive timed out ...

2017-01-19 16:06:08,482 INFO [main] de.cgh.screwminer.service.measurement.MeasurementService (MeasurementService.java:132) - Tasks submitted

Answer 1

From the Javadoc of invokeAll:

Returns:
   a list of Futures representing the tasks, in the same sequential order as produced by the iterator for the given task list, each of which has completed

So yes invokeAll Tasks are finished.

What you can do is just hold the Executor in the class and submit each task in your forEach() which would do the same. You then get a list of Futures which you should check for errors.

you could do something like this:

getSensors().forEach(s -> {
    CompletableFuture<Void> cf = (s -> writerService.openWriteConnection(s)).exceptionally(ex -> errorhandling)
    exec.submit(cf)
});

CompletableFuture is a Java8 feature and lets you control errors nicely as you don't have to ask the Futures if they completed successfully (Which often leads to unexpected non logged errors)