Question

我有一个java类，它使用ProcessBuilder创建一个名为child的进程。子进程生成大量输出，我在一个单独的线程上耗尽，以防止主线程被阻塞。但是，稍后我需要等待输出线程完成/终止才能继续，我不知道该怎么做。我认为join（）是通常的方法，但在这种情况下我不确定如何做到这一点。这是java代码的相关部分。

    // Capture output from process called child on a separate thread

    final StringBuffer outtext = new StringBuffer("");
    new Thread(new Runnable() {
        public void run() {
            InputStream in = null;
            in = child.getInputStream();
            try {
                if (in != null) {
                    BufferedReader reader = new BufferedReader(new InputStreamReader(in));
                    String line = reader.readLine();
                    while ((line != null)) {
                        outtext.append(line).append("\n");
                        ServerFile.appendUserOpTextFile(userName, opname, outfile, line+"\n");
                        line = reader.readLine();
                    }
                }
            } catch (IOException iox) {
                throw new RuntimeException(iox);
            }
        }
    }).start();

    // Write input to for the child process on this main thread
    //
    String intext = ServerFile.readUserOpTextFile(userName, opname, infile);
    OutputStream out = child.getOutputStream();
    try {
        out.write(intext.getBytes());
        out.close();
    } catch (IOException iox) {
        throw new RuntimeException(iox);
    }

    //  ***HERE IS WHERE I NEED TO WAIT FOR THE THREAD TO FINISH ***

    // Other code goes here that needs to wait for outtext to get all
    // of the output from the process

    // Then, finally, when all the remaining code is finished, I return
    // the contents of outtext

    return outtext.toString();

Answer 1

您可以加入该主题。您将获得该线程的实例，并在需要时等待调用其join方法。

 Thread th = new Thread(new Runnable() {  ... } );
 th.start();
 //do work 
 //when need to wait for it to finish
 th.join();
 //th has now finished

其他人会建议使用CountdownLatch，CyclicBarrier甚至是Future，但我发现这是最容易实现的。

Answer 2

您必须将线程分配给变量，然后在此变量上调用join()。

Answer 3

final StringBuffer outtext = new StringBuffer("");  
Thread outputDrainThread = new Thread(new Runnable() {
    public void run() {
        // ... 
    }
}).start();

// ...

//  ***HERE IS WHERE I NEED TO WAIT FOR THE THREAD TO FINISH ***
outputDrainThread.join();    

// ...
return outtext.toString();

Java：如何使这个主线程等待新线程终止

3 个答案: