Java8 Stream 的并发

水深无声 2022-04-18 01:55 155阅读 0赞

转发：[https://blog.csdn.net/nianhua120/article/details/53406583][https_blog.csdn.net_nianhua120_article_details_53406583]

先看一下下面的程序

public class Main  
\{  
  public static void main(String\[\] args)\{  
    long startTime=System.currentTimeMillis();   //获取开始时间  
    LongStream.rangeClosed(1L, 10000L)  
    // .parallel()  
    .forEach(in->\{  
      Thread thread = Thread.currentThread();  
      System.out.println("thread: "+thread.getName()+", value: "+in);  
      try\{  
        Thread.sleep(5);  
      \}catch (Exception ex)\{  
        ex.printStackTrace();  
      \}  
    \});  
    long endTime=System.currentTimeMillis(); //获取结束时间  
    System.out.println("程序运行时间： "+(endTime-startTime)+"ms");

\}  
\}  
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结果

thread: main, value: 1  
thread: main, value: 2  
thread: main, value: 3  
thread: main, value: 4  
thread: main, value: 5  
thread: main, value: 6  
thread: main, value: 7  
thread: main, value: 8  
thread: main, value: 9  
thread: main, value: 10  
thread: main, value: 11  
thread: main, value: 12  
thread: main, value: 13  
thread: main, value: 14  
thread: main, value: 15  
thread: main, value: 16  
thread: main, value: 17  
thread: main, value: 18  
thread: main, value: 19  
thread: main, value: 20  
thread: main, value: 21  
thread: main, value: 22  
thread: main, value: 23  
thread: main, value: 24  
thread: main, value: 25  
...  
程序运行时间： 51166ms  
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可以看出这个和程序串行执行。

然后我们修改一下程序，添加了1个parrallel，如下

public class Main  
\{  
  public static void main(String\[\] args)\{  
    long startTime=System.currentTimeMillis();   //获取开始时间  
    LongStream.rangeClosed(1L, 10000L)  
    .parallel()  
    .forEach(in->\{  
      Thread thread = Thread.currentThread();  
      System.out.println("thread: "+thread.getName()+", value: "+in);  
      try\{  
        Thread.sleep(5);  
      \}catch (Exception ex)\{  
        ex.printStackTrace();  
      \}  
    \});  
    long endTime=System.currentTimeMillis(); //获取结束时间  
    System.out.println("程序运行时间： "+(endTime-startTime)+"ms");

\}  
\}

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运行结果为：

thread: main, value: 17968751  
thread: ForkJoinPool.commonPool-worker-4, value: 28222657  
thread: ForkJoinPool.commonPool-worker-2, value: 37194824  
thread: ForkJoinPool.commonPool-worker-5, value: 9375001  
thread: ForkJoinPool.commonPool-worker-1, value: 6250001  
thread: ForkJoinPool.commonPool-worker-6, value: 1  
thread: ForkJoinPool.commonPool-worker-3, value: 3125001  
thread: ForkJoinPool.commonPool-worker-7, value: 51914786  
thread: main, value: 17968752  
thread: ForkJoinPool.commonPool-worker-2, value: 37194825  
thread: ForkJoinPool.commonPool-worker-4, value: 28222658  
thread: ForkJoinPool.commonPool-worker-1, value: 6250002  
thread: ForkJoinPool.commonPool-worker-7, value: 51914787  
thread: ForkJoinPool.commonPool-worker-5, value: 9375002  
thread: ForkJoinPool.commonPool-worker-6, value: 2  
thread: ForkJoinPool.commonPool-worker-3, value: 3125002  
thread: ForkJoinPool.commonPool-worker-2, value: 37194826  
thread: ForkJoinPool.commonPool-worker-1, value: 6250003  
thread: ForkJoinPool.commonPool-worker-4, value: 28222659  
thread: main, value: 17968753  
thread: ForkJoinPool.commonPool-worker-7, value: 51914788  
thread: ForkJoinPool.commonPool-worker-5, value: 9375003  
thread: ForkJoinPool.commonPool-worker-3, value: 3125003  
thread: ForkJoinPool.commonPool-worker-6, value: 3  
thread: ForkJoinPool.commonPool-worker-2, value: 37194827  
thread: ForkJoinPool.commonPool-worker-1, value: 6250004  
thread: ForkJoinPool.commonPool-worker-4, value: 28222660  
thread: main, value: 17968754  
...  
程序运行时间： 6459ms  
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从时间上来看，并发执行只需要要6s，而串行需要51s。从结果来看，串行能保证输出的顺序性，并行不行。从内存利用率来看，并发内存占用高。如果你都CPU核更多，将会有更多的线程参与运算，进一步加快计算，符合现代的多核计算思想。

有兴趣的同学可以把睡眠的代码去掉，看看cpu使用率，并发情况下cpu使用率比较均匀。  
\---------------------   
作者：nianhua120   
来源：CSDN   
原文：https://blog.csdn.net/nianhua120/article/details/53406583   
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[https_blog.csdn.net_nianhua120_article_details_53406583]: https://blog.csdn.net/nianhua120/article/details/53406583