运行外部进程的非阻塞线程

Question

我创建了一个 Java GUI 应用程序，它充当许多低级外部进程的包装器。该实用程序按原样运行，但迫切需要一项重大改进。

我希望我的外部进程以非阻塞方式运行，这将允许我并行处理其他请求。简而言之，我希望能够在生成数据时处理来自外部进程的数据。但似乎我检查外部进程是否仍在运行的基本尝试正在阻塞。

以下是我的 ExternalProcess 课程的摘录。有关线程和阻塞的特定 Java 功能问题，请参阅内联 cmets。

public void Execute()
{
    System.out.println("Starting thread ...\n");
    Runner = new Thread(this, "ExternalProcessTest");
    Runner.run();
    System.out.println("Ending thread ...\n");
}

public void run() 
{
    System.out.println("In run method ...\n");  // Debug purposes only. 
        // Show that we are in the run loop.
    try
    {
        // Execute string command SomeCommand as background process ...
        Process = Runtime.getRuntime().exec(SomeCommand);
        while(IsRunning())
        {
            // External process generates file IO.  I want to process these
            // files inside this loop.  For the purpose of this demo I have
            // removed all file processing to eliminate it as the cause
            // of blocking.  THIS ROUTINE STILL BLOCKS!
            Thread.sleep(1000);
        }
    }
    catch(Exception e)
    {
        System.out.println(e);
    }
    System.out.println("Exiting run method ...\n");  // Debug purposes only.
        // Show that we are exiting the run loop.
}

// Process (instantiated from Runtime.getRuntime().execute doesn't supports
// either fire-and-forget backgrounding (non-blocking) or you can wait for 
// the process to finish using the waitFor() method (blocking).  I want to
// be able to execute a non-blocking external process that I monitor via
// threading allowing me to process the external process file IO as it is
// created.  To facilitate this goal, I have created an isRunning() method
// that uses the exitValue() method.  If the process is still running, a 
// call to exitValue() will throw an IllegalThreadStateException exception.
// So I simply catch this execption to test if the background process is
// finished -- at which point I can stop processing file IO from the 
// process.  Is this the source of the blocking?  If so, is there another
// way to do this?
public boolean IsRunning()
{
    boolean isRunning = false;
    try
    {
        int exitVal = Process.exitValue();
    }
    catch(IllegalThreadStateException e)
    {
        isRunning = true;
    }
    return isRunning;
}

Answer 1

Thread 上的 run() 方法实际上并没有启动新线程，请尝试使用 Thread.start() 代替。

Answer 2

Runner = new Thread(this, "ExternalProcessTest");
Runner.run();

run() 方法具有欺骗性的名称。因为Thread 实现了Runnable 接口，所以run() 方法是公开的，但是不是当你想启动一个新线程时调用的正确方法。调用run() 会导致线程代码在当前线程中运行。

您必须调用start() 来实例化一个新线程：

Runner = new Thread(this, "ExternalProcessTest");
Runner.start();