java - 如何在多线程应用程序中衡量代码性能？

Question

我目前正在从事一个项目，该项目不使用任何性能评估工具来计算代码执行所花费的时间。

相反，我在代码的开头和结尾使用long <variableName> = System.nanoTime();，并减去它们以获得完成执行所需的时间。

直到我开始在多线程代码中使用它之前，它的运行情况都很好。

public class DataEntry {


    public static void main(String[] args) {

        long l = System.nanoTime();

        /*
        *  Regular Multithreading code to generate 'n' number of threads to
        *  perform a certain task.
        */


        System.out.println("Total Execution Time Is : "+((System.nanoTime()-l)/1000000.0)+" milli seconds");
    }
}

我在这里面临的问题是，在用户创建的线程完成任务之前，我的 main()线程完成了执行。

我的意思是，我得到这样的输出...

Total Execution Time Is : 9.600147 milli seconds
Thread#1 :  Execution Over Bye Bye
Thread#2 :  Execution Over Bye Bye
Thread#3 :  Execution Over Bye Bye
Thread#4 :  Execution Over Bye Bye
Thread#5 :  Execution Over Bye Bye

All the child threads give their corresponding final o/p couple of seconds after main() has finished executing

我了解所有线程都彼此独立运行，并且我们可以使main sleep()直到所有 子线程完成其执行。

我想知道是否有一种方法可以使我防止任何线程等待对方，以便最后一个执行完毕的线程负责返回我的最终执行时间。

以下是代码

DataEntry.java

public class DataEntry {

    public static void main(String[] args) {

        long l = System.nanoTime();

//STRING THAT WILL BE USED TO DOWNLOAD THE MULTIPLE FILES

        String[] strDownload = {"https://unsplash.com/photos/n61ur6rT_F8/download?force=true",
                    "https://unsplash.com/photos/GLS3mY37RPo/download?force=true",
                    "https://unsplash.com/photos/v6asLq_dYzw/download?force=true",
                    "https://unsplash.com/photos/ePB2oGU8mb4/download?force=true",
                    "https://unsplash.com/photos/yEHQfGNKnZ4/download?force=true"};


        //CREATE A FIXED NUMBER OF THREADS BASED ON THE LENGTH OF THE INPUT STRING ARRAY
            for (int i = 0; i < strDownload.length; i++) {
                Thread t = new Thread(new ThreadsGeneration(strDownload[i]));   //PASSING THE i'th ELEMENT OF THE ARRAY AS THE PARAMETER FOR THE CONSTRUCTOR
                t.start();                                                      //CREATE THE THREAD
                System.out.println(t.getName()+"\n");

            }

            System.out.println("Total Execution Time Is : "+((double)(System.nanoTime()-l)/1000000)+" milli seconds");
        }
    }

ThreadGeneration.java

public class ThreadsGeneration implements Runnable{

    private static String string;

    public ThreadsGeneration(String string) {
        ThreadsGeneration.string = string;
    }

    @Override
    public void run() {
        System.out.println("Inside RUN");
        DownloadManager.getData(string);

    }   
}

DownloadManager.java

public class DownloadManager {


    public static void getData(String strDownload) {


        String strDestination = "C:\\Users\\admin\\Desktop\\"+Math.random()+".jpg";

        try {       

            printData(strDownload,strDestination);

        } catch (Exception e) {

            e.printStackTrace();
        }
    }

    private static synchronized void printData(String strDownload, String strDestination) throws Exception {

        URL url = new URL(strDownload);
        ReadableByteChannel rbc = Channels.newChannel(url.openConnection().getInputStream());
        FileOutputStream fos = new FileOutputStream(strDestination);
        fos.getChannel().transferFrom(rbc, 0, Long.MAX_VALUE);
        fos.close();
        rbc.close();
        System.out.println("Everything done");
    }
}

Answer 1

我可以想到两种方式:

通过调用.join()将所有线程与主线程连接起来，然后打印出所有线程连接所需的时间。这样，主线程将轻松地打印花费的时间。
Main在这种情况下不 sleep 。它只是在等待。

在运行代码的末尾，让您的线程打印所花费的时间。这样，您可以看到每个线程的单独时间，并花费一些脑力周期自己计算总体执行时间。