JUC學習筆記（一）https://www.cnblogs.com/lm66/p/15118407.html
JUC學習筆記（二）https://www.cnblogs.com/lm66/p/15118813.html

1、執行緒間通訊

執行緒間通訊的模型有兩種：共享記憶體和訊息傳遞，以下方式都是基本這兩種模型來實現的。我們來基本一道面試常見的題目來分析
場景---兩個執行緒，一個執行緒對當前數值加 1，另一個執行緒對當前數值減 1,要求用執行緒間通訊

1.1、synchronized 方案

public class ThreadDemo1 {

    public static void main(String[] args) {
        Share share = new Share();

        new Thread(() -> {
            for (int i = 0; i < 10; i++) {
                try {
                    share.increment();
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        }, "AA").start();

        new Thread(() -> {
            for (int i = 0; i < 10; i++) {
                try {
                    share.decrement();
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        }, "BB").start();
    }

}

class Share {

    private int num = 0;

    public synchronized void increment() throws Exception {
        while (num != 0) {
            this.wait();
        }
        num++;
        System.out.println(Thread.currentThread().getName() + "::" + num);
        this.notifyAll();

    }

    public synchronized void decrement() throws Exception {
        while (num != 1) {
            this.wait();
        }
        num--;
        System.out.println(Thread.currentThread().getName() + "::" + num);
        this.notifyAll();
    }
}
 

1.2、Lock方案

public class ThreadDemo2 {

    public static void main(String[] args) {
        Share2 share = new Share2();

        new Thread(() -> {
            for (int i = 0; i < 10; i++) {
                try {
                    share.increment();
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        }, "AA").start();

        new Thread(() -> {
            for (int i = 0; i < 10; i++) {
                try {
                    share.decrement();
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        }, "BB").start();
    }

}

class Share2 {

    private Lock lock = new ReentrantLock();
    private Condition condition = lock.newCondition();

    private int num = 0;

    public void increment() throws Exception {
        lock.lock();
        try {
            while (num != 0) {
                condition.await();
            }
            num++;
            System.out.println(Thread.currentThread().getName() + "::" + num);
            condition.signalAll();
        } finally {
            lock.unlock();
        }

    }

    public void decrement() throws Exception {
        lock.lock();
        try {
            while (num != 1) {
                condition.await();
            }
            num--;
            System.out.println(Thread.currentThread().getName() + "::" + num);
            condition.signalAll();
        } finally {
            lock.unlock();
        }
    }
}
 

1.3、執行緒間定製化通訊

1.3.1、案例介紹

問題: A 執行緒列印 5 次 A，B 執行緒列印 10 次 B，C 執行緒列印 15 次 C,按照此順序迴圈 10 輪

1.3.2、實現流程

public class ThreadDemo3 {

    public static void main(String[] args) {
        ShareResource shareResource = new ShareResource();
        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                try {
                    shareResource.print5(i);
                } catch (Exception e) {
                }
            }
        },"AA").start();
        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                try {
                    shareResource.print10(i);
                } catch (Exception e) {
                }
            }
        },"BB").start();
        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                try {
                    shareResource.print15(i);
                } catch (Exception e) {
                }
            }
        },"CC").start();
    }
}

class ShareResource {
    // 定義標誌位
    private int flag = 1;
    // 建立Lock鎖
    private Lock lock = new ReentrantLock();
    private Condition c1 = lock.newCondition();
    private Condition c2 = lock.newCondition();
    private Condition c3 = lock.newCondition();

    public void print5(int loop) throws Exception {
        lock.lock();
        try {
            // 判斷。防止虛假喚醒
            while (flag != 1) {
                // 等待
                c1.await();
            }
            for (int i = 0; i < 5; i++) {
                System.out.println(Thread.currentThread().getName() + "::" + loop);
            }
            // 修改標誌位
            flag = 2;
            // 通知
            c2.signal();
        } finally {
            lock.unlock();
        }
    }

    public void print10(int loop) throws Exception {
        lock.lock();
        try {
            while (flag != 2) {
                c2.await();
            }
            for (int i = 0; i < 10; i++) {
                System.out.println(Thread.currentThread().getName() + "::" + loop);
            }
            flag = 3;
            c3.signal();
        } finally {
            lock.unlock();
        }
    }

    public void print15(int loop) throws Exception {
        lock.lock();
        try {
            while (flag != 3) {
                c3.await();
            }
            for (int i = 0; i < 15; i++) {
                System.out.println(Thread.currentThread().getName() + "::" + loop);
            }
            flag = 1;
            c1.signal();
        } finally {
            lock.unlock();
        }
    }
}