线程池execute和submit的区别是什么?有什么同?

KLQ 2020-06-29 15:13:31 java常见问答 5918

对于线程池execute以及submit你都了解吗?那么execute和submit这两者之间的区别是什么呢?很多人表示不大清楚,下面一起来了解一下。

代码:

public class ThreadPool_Test
{
    public static void main(String[] args) throws InterruptedException, ExecutionException
    {
        ExecutorService pool = Executors.newCachedThreadPool();
        pool.execute(new MyRunner());
        Future < String > future = pool.submit(new MyCaller());
        String ret = future.get();
        System.out.println(ret);
    }
}
class MyCaller implements Callable < String >
{
    @Override
    public String call() throws Exception
    {
        System.out.println("calling");
        return "return_from_call";
    }
}
class MyRunner implements Runnable
{
    @Override
    public void run()
    {
        System.out.println("running");
    }
}

execute方法执行runnable 任务,submit方法执行callable任务,callable任务有返回值,但是,runnable不一样,runnable任务是void的,没有返回值。

// void java.util.concurrent.ThreadPoolExecutor
final void runWorker(Worker w)
{
    Thread wt = Thread.currentThread();
    Runnable task = w.firstTask;
    w.firstTask = null;
    w.unlock(); // allow interrupts
    boolean completedAbruptly = true;
    try
    {
        while (task != null || (task = getTask()) != null)
        {
            w.lock();
            if ((runStateAtLeast(ctl.get(), STOP) ||
                    (Thread.interrupted() &&
                        runStateAtLeast(ctl.get(), STOP))) &&
                !wt.isInterrupted())
                wt.interrupt();
            try
            {
                beforeExecute(wt, task);
                Throwable thrown = null;
                try
                {
                    task.run();
                }
                catch (RuntimeException x)
                {
                    thrown = x;
                    throw x;
                }
                catch (Error x)
                {
                    thrown = x;
                    throw x;
                }
                catch (Throwable x)
                {
                    thrown = x;
                    throw new Error(x);
                }
                finally
                {
                    afterExecute(task, thrown);
                }
            }
            finally
            {
                task = null;
                w.completedTasks++;
                w.unlock();
            }
        }
        completedAbruptly = false;
    }
    finally
    {
        processWorkerExit(w, completedAbruptly);
    }
}

Runnable,task是MyRunner。

Callable,task是FutureTask。

submit方法的调用栈:

线程池execute和submit的区别

创建FutureTask对象,将Callable对象包裹起来,在run方法中调用Callable对象的方法,并且,设置返回值。

// java.util.concurrent.FutureTask.FutureTask
public FutureTask(Callable < V > callable)
{
    if (callable == null)
        throw new NullPointerException();
    this.callable = callable;
    this.state = NEW; // ensure visibility of callable
}
public void run()
{
    if (state != NEW ||
        !UNSAFE.compareAndSwapObject(this, runnerOffset
            , null, Thread.currentThread()))
        return;
    try
    {
        Callable < V > c = callable;
        if (c != null && state == NEW)
        {
            V result;
            boolean ran;
            try
            {
                result = c.call();
                ran = true;
            }
            catch (Throwable ex)
            {
                result = null;
                ran = false;
                setException(ex);
            }
            if (ran)
                set(result);
        }
    }
    finally
    {
        // runner must be non-null until state is settled to
        // prevent concurrent calls to run()
        runner = null;
        // state must be re-read after nulling runner to prevent
        // leaked interrupts
        int s = state;
        if (s >= INTERRUPTING)
            handlePossibleCancellationInterrupt(s);
    }
}

线程池execute以及submit的区别你都了解了吗?在java入门学习当中,线程池方面的问题是经常会碰到的,希望上面的文章可以对你有所帮助,更多java方面的常见问题,请继续通过本站来进行了解吧。

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