【多線程】雙線程交替打印1至100

一、內置鎖

• 同步：synchronized
• 協作：Object # wait/notify/notifyAll

public class PrintNumber {

    /**
     * 打印鎖，同一時刻僅有一個任務可以持有此鎖
     */
    private static Object lock = new Object();

    /**
     * 計數器
     */
    private static int counter = 1;

    /**
     * 計數器最大值
     */
    private static final int MAX_COUNTER = 100;

    public static void main(String args[]) {
        // 奇數打印線程
        Thread oddThread = new Thread() {
            @Override
            public void run() {
                // 請求打印鎖
                synchronized (lock) {
                    while (counter <= MAX_COUNTER) {
                        // counter爲奇數，打印counter並喚醒偶數打印線程
                        if (counter % 2 != 0) {
                            System.out.println("Thread1 : " + counter);
                            counter = counter + 1;
                            lock.notifyAll();
                        }
                        // counter爲偶數，掛起並等待偶數打印線程喚醒
                        else {
                            try {
                                lock.wait();
                            } catch (Exception e) {
                                e.printStackTrace();
                            }
                        }
                    }
                }
            }
        };

        // 偶數打印線程
        Thread evenThread = new Thread() {
            @Override
            public void run() {
                // 請求打印鎖
                synchronized (lock) {
                    while (counter <= MAX_COUNTER) {
                        // counter爲偶數，打印counter並喚醒奇數打印線程
                        if (counter % 2 == 0) {
                            System.out.println("Thread2 : " + counter);
                            counter = counter + 1;
                            lock.notifyAll();
                        }
                        // counter爲奇數，掛起並等待奇數打印線程喚醒
                        else {
                            try {
                                lock.wait();
                            } catch (Exception e) {
                                e.printStackTrace();
                            }
                        }
                    }
                }
            }
        };


        oddThread.start();
        evenThread.start();
    }

}

二、顯式鎖

• 同步：lock/unlock
• 協作：Condition # await/signal/signalAll

public class PrintNumber {

    /**
     * 打印鎖，同一時刻僅有一個任務可以持有此鎖
     */
    private static Lock lock = new ReentrantLock();

    private static Condition oddCondition = lock.newCondition();

    private static Condition evenCondition = lock.newCondition();

    /**
     * 計數器
     */
    private static int counter = 1;

    /**
     * 計數器最大值
     */
    private static final int MAX_COUNTER = 100;

    public static void main(String args[]) {
        // 奇數打印線程
        Thread oddThread = new Thread() {
            @Override
            public void run() {
                try {
                    // 請求打印鎖
                    lock.lock();
                    while (counter <= MAX_COUNTER) {
                        // counter爲奇數，打印counter並喚醒偶數打印線程
                        if (counter % 2 != 0) {
                            System.out.println("Thread1 : " + counter);
                            counter = counter + 1;
                            evenCondition.signalAll();
                        }
                        // counter爲偶數，掛起並等待偶數打印線程喚醒
                        else {
                            try {
                                oddCondition.await();
                            } catch (Exception e) {
                                e.printStackTrace();
                            }
                        }
                    }
                } finally {
                    // 釋放打印鎖
                    lock.unlock();
                }
            }
        };

        // 偶數打印線程
        Thread evenThread = new Thread() {
            @Override
            public void run() {
                try {
                    // 請求打印鎖
                    lock.lock();
                    while (counter <= MAX_COUNTER) {
                        // counter爲偶數，打印counter並喚醒奇數打印線程
                        if (counter % 2 == 0) {
                            System.out.println("Thread2 : " + counter);
                            counter = counter + 1;
                            oddCondition.signalAll();
                        }
                        // counter爲奇數，掛起並等待奇數打印線程喚醒
                        else {
                            try {
                                evenCondition.await();
                            } catch (Exception e) {
                                e.printStackTrace();
                            }
                        }
                    }
                } finally {
                    // 釋放打印鎖
                    lock.unlock();
                }
            }
        };

        oddThread.start();
        evenThread.start();
    }

}