Java IO 输入流在读取外部 C 程序的标准输出和标准错误时阻塞

Question

我几天前在这里发布了同样的问题(Java reading standard output from an external program using inputstream)，我发现了一些在阅读时处理阻塞的极好的建议(while(is.read()) != -1)) , 但我仍然无法解决问题。

看完这个类似问题的答案后，

Java InputStream blocking read (特别是 Guss 发布的答案)，

我开始相信，如果程序是交互式的，那么使用 is.read() != -1 条件循环输入流是行不通的(也就是说，它需要来自用户的多个输入，并在后续输入时呈现额外的输出，并且只有在给出明确的退出命令时程序才会退出)。我承认我对多线程知之甚少，但我认为我需要的是一种机制，可以在需要用户输入时立即暂停输入流线程(stdout、stderr 各一个)，并在输入完成后恢复提供以防止阻塞。以下是我当前的代码，它在指示的行上遇到了一个 block :

EGMProcess egm = new EGMProcess(new String[]{directory + "/egm", "-o",
                "CasinoA", "-v", "VendorA", "-s", "localhost:8080/gls/MessageRobot.action ",
                "-E", "glss_env_cert.pem", "-S", "glss_sig_cert.pem", "-C", "glsc_sig_cert.pem",
                "-d", "config", "-L", "config/log.txt", "-H", "GLSA-SampleHost"}, new String[]{"PATH=${PATH}"}, directory);


    egm.execute();

    BufferedReader stdout = new BufferedReader(new InputStreamReader(egm.getInputStream()));
    BufferedReader stderr = new BufferedReader(new InputStreamReader(egm.getErrorStream()));

    EGMStreamGobbler stdoutprocessor = new EGMStreamGobbler(stdout, egm);
    EGMStreamGobbler stderrprocessor = new EGMStreamGobbler(stderr, egm);

    BufferedWriter stdin = new BufferedWriter(new OutputStreamWriter(egm.getOutputStream()));


    stderrprocessor.run(); //<-- the block occurs here!
    stdoutprocessor.run();


    //EGM/Agent test cases


        //check bootstrap menu
        if(!checkSimpleResult("******** EGM Bootstrap Menu **********", egm))
        {
            String stdoutdump = egm.getStdOut();
            egm.cleanup();
            throw new Exception("can't find '******** EGM Bootstrap Menu **********'" +
                "in the stdout" + "\nStandard Output Dump:\n" + stdoutdump);
        }

        //select bootstrap
        stdin.write("1".toCharArray());
        stdin.flush();

        if(!checkSimpleResult("Enter port to receive msgs pushed from server ('0' for no push support)", egm)){
            String stdoutdump = egm.getStdOut();
            egm.cleanup();
            throw new Exception("can't find 'Enter port to receive msgs pushed from server ('0' for no push support)'" +
                    "in the stdout" + "\nStandard Output Dump:\n" + stdoutdump);
        }


...
  
 

<p>
public class EGMStreamGobbler implements Runnable{</p>

private BufferedReader instream;
private EGMProcess egm;

public EGMStreamGobbler(BufferedReader isr, EGMProcess aEGM)
{
    instream = isr;
    egm = aEGM;
}

public void run() 
{
    try{
        int c;
        while((c = instream.read()) != 1)
        {
            egm.processStdOutStream((char)c);
        }

    }
    catch(IOException e)
    {
        e.printStackTrace();
    }
}
 

}

对于代码的长度，我深表歉意，但我的问题是，

1) 有什么方法可以在不使用 read() 的情况下控制接收输入流(stdout、stderr)的过程？还是我只是执行得很糟糕？

2) 多线程是否是开发接收输入流和写入输出过程的正确策略？

PS:如果有人能提供类似问题的解决方案，那将对我有很大帮助!

Answer 1

代替

stderrprocessor.run(); //<-- the block occurs here!
stdoutprocessor.run();

您需要启动线程:

Thread errThread = new Thread(stderrprocessor);
errThread.setDaemon( true );
errThread.start();

Thread outThread = new Thread(stdoutprocessor);
outThread.setDaemon( true );
outThread.start();

run()只是Runnable中指定的一个方法。 Thread.start() 在新的 Thread 中调用 Runnable 上的 run()。