Java多线程: why is execution not stopping at join()?

Question

我有一个模块，可以在开始时从文件中反序列化一堆资源。每个都需要时间，所以我想以多线程方式实现它，以便每个线程摄取单个资源。根据我在网上找到的一些示例，我编写了这个测试类，它代表我的主模块的资源摄取步骤。

public class MultiThreadedResourceIngest {

    private static ResourceClass1 r1 = null;
    private static ResourceClass2 r2 = null;
    private static ResourceClass3 r3 = null;

    static class ResourceReader extends Thread {
        private Thread t = null;
        private int id = -1;
        private String path2read = null;

        ResourceReader( final int id, final String path2read){
           this.id = id;
           this.path2read = path2read;
        }

        public void run() {

           if (path2read != null && path2read.length() > 0)
           {
              switch (id) {
                 case 0:
                    r1 = new ResourceClass1(path2read);
                    break;
                 case 1:
                    r2 = new ResourceClass2(path2read);
                    break;
                 case 2:
                    r3 = new ResourceClass3(path2read);
                    break;
                 default:
                    break;
              }

           }
           log.info(String.format("Thread with id=%d and path=%s exiting", id, path2read));
        }

        public void start ()
        {
           if (t == null)
           {
              t = new Thread (this);
              t.start ();
           }
        }

    }

    public static void main(String[] args) {

        final String[] paths = new String[] {"path1", "path2", "path3"};

        log.info("STARTING MTHREADED READ");
        ArrayList<ResourceReader> rrs = new ArrayList<ResourceReader>();
        for (int i=0; i < paths.length; i++)
        {
           ResourceReader rr = new ResourceReader(i,paths[i]);
           rr.start();
           rrs.add(rr);
        }

        log.info("JOINING");
        for (ResourceReader rr: rrs)
        {
           try {
              rr.join();
           } catch (InterruptedException e) {
              // Thread interrupted
              e.printStackTrace();
           }
        }

        // Want to reach this point only when all resources are ingested
        //
        log.info("MTHREADED FINISHED");
    }

}

所以这里我有 3 个资源，我想在所有线程完成后到达标记为 //Want to get this point... 的点。这就是我实现 join() 循环的原因，只不过它没有按预期工作，即日志如下所示:

STARTING MTHREADED READ
Thread with id=0 and path=path1 exiting
JOINING
Thread with id=2 and path=path3 exiting
MTHREADED FINISHED
Thread with id=1 and path=path2 exiting

我需要更改什么才能等到所有资源都被读取后再继续？

Answer 1

您声明了 类 ResourceReader 扩展了 Thread，但您创建了另一个类并在 start 内启动它:

          t = new Thread (this);
          t.start ();

您应该加入此线程，而不是

          rr.join();

因此，只需删除 ResourceReader 中的 start() 方法，一切都会正常工作。