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，按照用户指定的时序要求，在线程内完成任务的执行。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时间的 + delta 范围内。例如，如果用户想在 5 秒内完成程序，根据代码运行的 CPU，它可能在 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 将为特定版本的 JVM 提供的最低延迟。基于该检测代码，可以将 delta 值添加到如下行：if (( taskRunTime > patience+delta) && t.isAlive())，以便系统为任务执行时间带来更精确的结果。请给点建议。

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");

    }
}

来自 Intel Centrino 1.7 Ghz 机器的示例输出（Java HotSpot(TM) Client VM（build 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 behaviour of Thread.sleep 的内容以及其他可能有用的与线程和 Java 相关的内容。

简短的回答是，您将获得的粒度取决于很多因素，其中一些是动态的。按照您的建议对其进行检测是前进的一种方式。关于检测需要考虑的事项包括：

• 在给定条件下实际睡眠与要求睡眠的行为（有关不同条件下一些典型行为的说明，请参阅我的文章）
• 给定条件下的线程中断延迟（部分取决于 CPU 负载、系统的调度策略...）

另外，考虑改进控制循环，使其本质上 (a) 休眠所需的时间（在循环中，确保时间已休眠），并且 (b) 在超时后中断线程。

顺便说一句，请始终使用 System.nanoTime() 作为您的计时。 否则，由于 System.currentTimeMillis() 在某些系统下的粒度很差，您只会感到困惑。

Answer 2

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

您不应该在 Java 1.5 之后编写自己的线程