确定 Java 程序的确定性线程执行

Question

我编写了一个非常简单的玩具程序，根据用户指定的计时要求完成线程内任务的执行。 代码和示例输出如下。 发生的情况是，每次运行代码时，任务完成时间都会在用户指定的时间的 + 增量范围内。 例如，如果用户想要在 5 秒内完成程序，根据代码运行的 CPU，它可能会在 5093 或 5012 毫秒内完成。 我想添加一些代码，这些代码可以自动确定特定 CPU 为特定版本的 JVM 提供的最低延迟。 基于该检测代码，可以将 delta 值添加到行中，例如： if (( taskRunTime > Patience+delta) && t.isAlive()) 以便系统带来更精确地执行任务计时。 请给一些建议。

代码：

public class ThreadExample 
{


    static void threadMessage(String message) 
    {
        String threadName = Thread.currentThread().getName();
        System.out.format("%s: %s%n", threadName, message);
    }

    private static class MessageLoop implements Runnable 
    {
        public void run() 
        {
            String importantInfo[] = 
            {
                "A new integrated approach to programming",
                "The innovative approach of the system",
                "The input of a tracking system",
                "A simulation system is then used for collision checking"
            };
            try 
                {
                    for (int i = 0; i < importantInfo.length; i++) 
                        {

                            Thread.sleep(4000);
                            threadMessage(importantInfo[i]);
                        }
                } 
                catch (InterruptedException e) 
                    {
                        threadMessage("I wasn't done!");
                    }
        }
    }

    public static void main(String args[]) throws InterruptedException 
    {


        //Delay, in milliseconds before we interrupt MessageLoop
        long patience = 1000 * 60 * 60;

        //If command line argument present, gives patience in seconds.
        if (args.length > 0) 
        {
            try {
                patience = Long.parseLong(args[0]) * 1000;
            } catch (NumberFormatException e) {
                System.err.println("Argument must be an integer.");
                System.exit(1);
            }

        }

        threadMessage("Starting MessageLoop thread");
        long startTime = System.currentTimeMillis(),taskRunTime=0;
        Thread t = new Thread(new MessageLoop());
        t.start();

        threadMessage("Waiting for MessageLoop thread to finish");
        //loop until MessageLoop thread exits
        while (t.isAlive()) 
        {
            threadMessage("Still waiting...");
            //Wait maximum of 1 second for MessageLoop thread to finish.
            t.join(100);
            taskRunTime=System.currentTimeMillis() - startTime;
            if (( taskRunTime > patience) && t.isAlive()) 
            {
                threadMessage("Tired of waiting...task is running longer than the patience you set or the default!");
                t.interrupt();
                t.join();
            }

        }
        threadMessage("Finally out of thread!");
        System.out.println("Time to complete task="+taskRunTime+"ms");

    }
}

Intel Centrino 1.7 Ghz 机器的示例输出（Java HotSpot(TM) 客户端 VM（版本 10.0-b23，混合模式））

java -jar ThreadExample.jar 5
main: Starting MessageLoop thread
main: Waiting for MessageLoop thread to finish
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
Thread-0: A new integrated approach to programming
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Still waiting...
main: Tired of waiting...task is running longer than the patience you set or the default!
Thread-0: I wasn't done!
main: Finally out of thread!

Answer 1

我还写了一些关于 Thread.sleep 行为 和其他内容与线程和 Java 相关的可能有用的东西。

简而言之，您将获得的粒度取决于很多因素，其中一些因素是动态的。 按照您的建议进行检测是前进的一种方法。 您需要考虑的事项包括：

• 给定条件下实际睡眠与请求的行为（请参阅我的文章，了解不同条件下的一些典型行为的说明）
• 给定条件下的线程中断延迟（部分取决于 CPU 负载、调度策略）系统...）

此外，请考虑改进控制循环，以便它本质上（a）休眠所需的时间（在循环中，确保休眠时间），以及（b）在超时后中断线程。

顺便说一句，请始终使用 System.nanoTime() 进行计时。否则，您只会因为某些系统下 System.currentTimeMillis() 的粒度较差而造成混乱。

Answer 2

我建议您查看 Java Real Time： http://en.wikipedia.org/wiki/Real_time_Java
另请查看： http://java.sun .com/j2se/1.5.0/docs/guide/concurrency/overview.html

在 Java 1.5 之后，您不应该编写自己的线程