public class NumberPrint implements Runnable {
private int state = 1;
private int n = 1;
// 使用lock做锁
private ReentrantLock lock = new ReentrantLock();
// 获得lock锁的3个分支条件
private Condition c1 = lock.newCondition();
private Condition c2 = lock.newCondition();
private Condition c3 = lock.newCondition();
@Override
public void run() {
new Thread(new Runnable() {
public void run() {
for (int i = 0; i < 5; i++) {
try {
// 线程1获得lock锁后, 其他线程将无法进入需要lock锁的代码块.
// 在lock.lock()和lock.unlock()之间的代码相当于使用了synchronized(lock){}
lock.lock();
while (state != 1)
try {
// 线程1竞争到了lock, 但是发现state不为1, 说明此时还未轮到线程1打印.
// 因此线程1将在c1上wait
// 与解法一不同的是, 三个线程并非在同一个对象上wait, 也不由同一个对象唤醒
c1.await();
} catch (InterruptedException e) {
e.printStackTrace();
}
// 如果线程1竞争到了lock, 也通过了state判定, 将执行打印任务
for (int j = 0; j < 5; j++) {
System.out.println(Thread.currentThread().getName()
+ ": " + n++);
}
System.out.println();
// 打印完成后将state赋值为2, 表示下一次的打印任务将由线程2执行
state = 2;
// 唤醒在c2分支上wait的线程2
c2.signal();
} finally {
// 打印任务执行完成后需要确保锁被释放, 因此将释放锁的代码放在finally中
lock.unlock();
}
}
}
}, "线程1").start();
new Thread(new Runnable() {
public void run() {
for (int i = 0; i < 5; i++) {
try {
lock.lock();
while (state != 2)
try {
c2.await();
} catch (InterruptedException e) {
e.printStackTrace();
}
for (int j = 0; j < 5; j++) {
System.out.println(Thread.currentThread().getName()
+ ": " + n++);
}
System.out.println();
state = 3;
c3.signal();
} finally {
lock.unlock();
}
}
}
}, "线程2").start();
new Thread(new Runnable() {
public void run() {
for (int i = 0; i < 5; i++) {
try {
lock.lock();
while (state != 3)
try {
c3.await();
} catch (InterruptedException e) {
e.printStackTrace();
}
for (int j = 0; j < 5; j++) {
System.out.println(Thread.currentThread().getName()
+ ": " + n++);
}
System.out.println();
state = 1;
c1.signal();
} finally {
lock.unlock();
}
}
}
}, "线程3").start();
}
public static void main(String[] args) {
new NumberPrint().run();
}
}
