线程间的通信

题目一：

实现一个线程对一个变量进行加一，另一个线程对一个变量减一。交替10轮 初始值为0。

class AirConditioner {
    private int number = 0;

    public synchronized void increment() throws InterruptedException {
        if (number != 0) {
            this.wait();
        }
        number++;
        System.out.println(Thread.currentThread().getName() + "\t" + number);
        this.notifyAll();

    }

    public synchronized void decrement() throws InterruptedException {
        if (number == 0) {
            this.wait();
        }
        number--;
        System.out.println(Thread.currentThread().getName() + "\t" + number);
        this.notifyAll();
    }


}

public class ThreadWaitNotifyDemo {
    public static void main(String[] args) {
        AirConditioner airConditioner = new AirConditioner();
        new Thread(() -> {
            try {
                for (int i = 0; i < 10; i++) {
                    airConditioner.increment();
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }, "A").start();

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

该版本有虚假唤醒问题，当有四个线程的时候，就会出错。

多线程中的判断只能使用 while 不能使用 if

class AirConditioner {
    private int number = 0;

    public synchronized void increment() throws InterruptedException {
        while (number != 0) {
            this.wait();
        }
        number++;
        System.out.println(Thread.currentThread().getName() + "\t" + number);
        this.notifyAll();

    }

    public synchronized void decrement() throws InterruptedException {
        while (number == 0) {
            this.wait();
        }
        number--;
        System.out.println(Thread.currentThread().getName() + "\t" + number);
        this.notifyAll();
    }
}

使用lock锁

class AirConditioner {
    private final ReentrantLock lock = new ReentrantLock();
    private final Condition condition = lock.newCondition();


    private int number = 0;

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

    }

    public void decrement() throws InterruptedException {
        lock.lock();
        try {
            while (number == 0) {
                condition.await();
            }
            number--;
            System.out.println(Thread.currentThread().getName() + "\t" + number);
            condition.signalAll();
        } finally {
            lock.unlock();
        }

    }


}

public class ThreadWaitNotifyDemo {
    public static void main(String[] args) {
       ...
       ...
}

题目二：

多线程之间按顺序调用，A打印5次，B打印10次，C打印15次，按顺序来10轮。

class ShareResource {
    ReentrantLock lock = new ReentrantLock();
    Condition condition1 = lock.newCondition();
    Condition condition2 = lock.newCondition();
    Condition condition3 = lock.newCondition();

    private int number = 1;

    public void print(int count) {
        if (count == 5) {
            lock.lock();
            try {
                while (number != 1) {
                    condition1.await();
                }
                for (int i = 0; i < count; i++) {
                    System.out.println(Thread.currentThread().getName() + "\t" + i);
                }
                number = 2;
                condition2.signal();
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                lock.unlock();
            }
        } else if (count == 10) {
            lock.lock();
            try {
                while (number != 2) {
                    condition2.await();
                }
                for (int i = 0; i < count; i++) {
                    System.out.println(Thread.currentThread().getName() + "\t" + i);
                }
                number = 3;
                condition3.signal();
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                lock.unlock();
            }
        } else if (count == 15) {
            lock.lock();
            try {
                while (number != 3) {
                    condition3.await();
                }
                for (int i = 0; i < count; i++) {
                    System.out.println(Thread.currentThread().getName() + "\t" + i);
                }
                number = 1;
                condition1.signal();
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                lock.unlock();
            }
        }

    }
}

public class ThreadOrderAccess {
    public static void main(String[] args) {
        ShareResource shareResource = new ShareResource();

        new Thread(() -> {
            for (int i = 0; i < 10; i++) {
                shareResource.print(5);
            }
        }, "A").start();
        new Thread(() -> {
            for (int i = 0; i < 10; i++) {
                shareResource.print(10);
            }
        }, "B").start();
        new Thread(() -> {
            for (int i = 0; i < 10; i++) {
                shareResource.print(15);
            }
        }, "C").start();
    }
}