Java併發編程入門（十五）CyclicBarrier應用場景

時間 2019-11-07

標籤 java 併發編程入門十五 cyclicbarrier 應用場景欄目 Java 简体版

原文原文鏈接

Java極客 | 做者 / 鏗然一葉這是Java極客的第 43 篇原創文章

1、應用場景

現實生活作中有不少這樣的場景：作F前須要等待A,B,C,D,E完成，A,B,C,D,E能夠併發完成，沒有特定順序，而且F作完後又從新開始，例如：組裝汽車前須要先生產輪胎，車門，車身等等。這個場景的特徵爲：java

1.組裝汽車前有N件事情要作，每件事情都作完後才能組裝汽車。編程

2.每件事情能夠並行處理，沒有前後順序，於是提升了效率。緩存

3.組裝好一輛汽車後繼續生產和組裝下一輛。(固然如今全部零件都是批量生產，不是一個個來的，咱們假設是人工造的限量版賓利，一量量來的。）安全

圍繞造車，整個過程以下：bash

在應用程序中處理並行操做時也跟上述場景相似，碰到這種場景時能夠經過java併發工具CyclicBarrier來實現。

2、Show me code

代碼類結構以下：併發

I、MakeCarBody.java

public class MakeCarBody implements Runnable {

    private CyclicBarrier cyclicBarrier;

    public MakeCarBody(CyclicBarrier cyclicBarrier) {
        this.cyclicBarrier = cyclicBarrier;
    }

    public void run() {
        exec();
    }

    /** * 模擬模擬造車身 */
    private void exec() {
        //造完後繼續造下一個
        while(true) {
            try {
                System.out.println("Start making car body...");

                long millis = ((int) (1 + Math.random() * (5 - 1 + 1))) * 1000;
                TimeUnit.MILLISECONDS.sleep(millis);
                System.out.println("Making car body is finished.");

                //等待其餘部件造完
                this.cyclicBarrier.await();

            } catch (InterruptedException e) {
                e.printStackTrace();
            } catch (BrokenBarrierException e) {
                e.printStackTrace();
            }
        }
    }
}
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II、MakeCarDoor.java

public class MakeCarDoor implements Runnable {

    private CyclicBarrier cyclicBarrier;

    public MakeCarDoor(CyclicBarrier cyclicBarrier) {
        this.cyclicBarrier = cyclicBarrier;
    }

    public void run() {
        exec();
    }

    /** * 模擬造車門 */
    private void exec() {
        //造完後繼續造下一個
        while(true) {
            try {
                System.out.println("Start making car door...");

                long millis = ((int) (1 + Math.random() * (5 - 1 + 1))) * 1000;
                TimeUnit.MILLISECONDS.sleep(millis);
                System.out.println("Making car door is finished.");

                //等待其餘部件造完
                this.cyclicBarrier.await();

            } catch (InterruptedException e) {
                e.printStackTrace();
            } catch (BrokenBarrierException e) {
                e.printStackTrace();
            }
        }
    }
}
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III、MakeTire.java

public class MakeTire implements Runnable {

    private CyclicBarrier cyclicBarrier;

    public MakeTire(CyclicBarrier cyclicBarrier) {
        this.cyclicBarrier = cyclicBarrier;
    }

    public void run() {
        exec();
    }

    /** * 模擬造輪胎 */
    private void exec() {
        //造完後繼續造下一個
        while(true) {
            try {
                System.out.println("Start making tire...");

                long millis = ((int) (1 + Math.random() * (5 - 1 + 1))) * 1000;
                TimeUnit.MILLISECONDS.sleep(millis);
                System.out.println("Making tire is finished.");

                //等待其餘部件造完
                this.cyclicBarrier.await();

            } catch (InterruptedException e) {
                e.printStackTrace();
            } catch (BrokenBarrierException e) {
                e.printStackTrace();
            }
        }
    }
}
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IV、AssembleCar.java

public class AssembleCar implements Runnable {

    public void run() {
        try {
            System.out.println("Start assemble car...");

            //模擬組裝汽車
            long millis = ((int)(1+Math.random()*(5-1+1))) * 1000;
            TimeUnit.MILLISECONDS.sleep(millis);
            System.out.println("Making assemble care is finished.");
        }
        catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}
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V、CyclicBarrierTest.java

public class CyclicBarrierTest {
    public static void main(String[] args) {
        //有3個部件要造，造完後組裝汽車
        CyclicBarrier cyclicBarrier = new CyclicBarrier(3, new AssembleCar());

        Thread makeCarBody = new Thread(new MakeCarBody(cyclicBarrier));
        Thread makeCarDoor = new Thread(new MakeCarDoor(cyclicBarrier));
        Thread makeTire = new Thread(new MakeTire(cyclicBarrier));

        makeCarBody.start();
        makeCarDoor.start();
        makeTire.start();
    }
}
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輸出日誌：dom

Start making car door...
Start making tire...
Start making car body...
Making tire is finished.
Making car door is finished.
Making car body is finished.
Start assemble car...
Making assemble care is finished.
Start making car body...
Start making tire...
Start making car door...
Making car body is finished.
Making tire is finished.
Making car door is finished.
Start assemble car...
Making assemble care is finished.
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能夠看到CyclicBarrier的使用方式以下：函數

1.CyclicBarrier的構造函數有2個參數，第1個參數是聲明有幾個部件須要製造（有幾件事能夠並行），第2個參數是一個Runnable，此參數表明並行完以後要作的最後一件事情。工具

2.每一個部件造完後調用CyclicBarrier的await()方法等待啓動下一輪。post

3.當最後一個部件造完後則會自動調用CyclicBarrier構造函數中傳入的Runnable的實現類。

4.Runnable實現類實現完成後從新開始下一輪。