父进程和子进程之间的通信

Question

我有一个充当父进程的类。 在运行期间，它将创建许多子进程并同时运行它们。 每个子进程基本上都是一个HTTP客户端，该客户端连接到服务并从中获取数据。

当前，如果子进程之一由于任何原因停止工作，则父进程将通过重新启动同一子进程来重新建立连接。

子进程的断开连接可能是由多种原因引起的。 我想将从子进程断开连接的原因传达给父进程，并让父进程根据断开原因（套接字读取失败，找不到404，未授权401等）采取相应的措施。

可能吗？ 最短/最好的方法是什么？ 这是我的家长班：

public class Parent {
public static void main(String[] args){
    List<Process> PRlist = new ArrayList<Process>();
    List<String[]> commandsList = new ArrayList<String[]>();
    DateTimeFormatter frmt = DateTimeFormatter.ofPattern("hh:mm:ss");

    if (args.length == 2 && args[0].matches("-f")){
        String dir = System.getProperty("user.dir");
        String path = dir + "/" + args[1];
        try {
            FileReader fr = new FileReader(path);
            BufferedReader bf = new BufferedReader(fr);

            String line = "";
            while ((line = bf.readLine()) != null){
                String[] tk = line.split(" ");
                String[] cmd = {"java", "-jar", "Child.jar", "-a", tk[0], "-p", tk[1],
                        "-u", tk[2], "-pw", tk[3], "-m", tk[4], "-s", tk[5]};
                Process pr = new ProcessBuilder().inheritIO().command(cmd).redirectInput(Redirect.INHERIT).start();
                PRlist.add(pr); commandsList.add(cmd);
            }
        } 
        catch (FileNotFoundException ex) {ex.printStackTrace();} 
        catch (IOException ex) {ex.printStackTrace();}

        int streamnum = PRlist.size();

        while (true){
            for (int i = 0; i < streamnum; i++){
                if (!PRlist.get(i).isAlive()){
                    PRlist.get(i).destroy();
                    PRlist.remove(i);
                    try {
                        Process PR = new ProcessBuilder().inheritIO().command(commandsList.get(i)).redirectInput(Redirect.INHERIT).start();
                        System.out.println(commandsList.get(i)[12] + " stream re-established at " + LocalDateTime.now().format(frmt));
                        PRlist.add(i,PR);
                    } catch (IOException ex) {ex.printStackTrace();}
                }
            }

            try {
                Thread.sleep(5000);
            } catch (InterruptedException ex) {ex.printStackTrace();}
        }
    } else {
        System.out.println("No stream file was specified.");
    }
}}

任何帮助，将不胜感激。

Answer 1

也许您可以使用这些方法

**public ProcessBuilder.Redirect redirectError()**
Returns this process builder's standard error destination. Subprocesses   subsequently started by this object's start() method redirect their standard error to this destination. The initial value is Redirect.PIPE.
Returns:
this process builder's standard error destination

要么

public abstract int exitValue()
Returns the exit value for the subprocess.
Returns:
the exit value of the subprocess represented by this Process object. By convention, the value 0 indicates normal termination.
Throws:
IllegalThreadStateException - if the subprocess represented by this Process object has not yet terminated

Answer 2

举个例子

有点像

if (!PRlist.get(i).isAlive()){
    int exitCode=PRlist.get(i).exitValue();
    //Do something with exitValue

    PRlist.get(i).destroy();
    PRlist.get(i).destroy();
    PRlist.remove(i);
    try {
        Process PR = new ProcessBuilder().inheritIO().command(commandsList.get(i)).redirectInput(Redirect.INHERIT).start();
        System.out.println(commandsList.get(i)[12] + " stream re-established at " + LocalDateTime.now().format(frmt));
         PRlist.add(i,PR);
         } catch (IOException ex) {ex.printStackTrace();}
         }

使用errorStream的示例可能更复杂，但是其思想是通过文本处理查看在errorStream中发布的异常。

Answer 3

好的，使用Java线程，您可以这样做：

class MyThreadedApp {

    // main() here

    /**
     * Starting a new thread
     */
    private void start() {
        new Thread(() -> {
            try {
                new Worker().run();
            } catch (Exception ex) {
                threadEnded(ex);
            }
        }).start();
    }

    /**
     * Handle errors
     * 
     * @param ex Error
     */
    private void threadEnded(Exception ex) {
        System.out.println(ex.getMessage());
    }
}

/**
 * My worker thread
 */
class Worker {

    void run() throws IOException {
        // Do my stuff here
    }
}

这是一个基本示例，仅用于演示数据流。 实际上，您可以使用提到的@lscoughlin技术。