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题目：实现一个容器，包含 add 和 size 两个方法。写两个线程，线程 1 添加 10 个元素到容器中，线程 2 监控元素的个数，当元素个数达到 5 时，线程 2 给出提示。
下面给出 4 种解法
等待通知机制
synchronized
public class WithWaitAndNotify<E> {
List<E> list = new ArrayList();
public void add(E e) {
list.add(e);
}
public int size() {
return list.size();
}
public static void main(String[] args) {
WithWaitAndNotify<Integer> c = new WithWaitAndNotify();
final Object lock = new Object();
new Thread(() -> {
System.out.println("t2启动");
synchronized (lock) {
if (c.size() != 5) {
try {
lock.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
System.out.println("t2结束");
// 唤醒t1
lock.notify();
}
}, "t2").start();
new Thread(() -> {
System.out.println("t1启动");
synchronized (lock) {
for (int i = 0; i < 10; i++) {
c.add(i);
System.out.println("add " + i);
if (c.size() == 5) {
// 唤醒t2
lock.notify();
try {
// 提前释放锁，让t2执行，否则需要等到t1的所有代码执行完才会释放锁
lock.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
}, "t1").start();
}
}
Condition
public class WithCondition<E> {
List<E> list = new ArrayList();
public void add(E e) {
list.add(e);
}
public int size() {
return list.size();
}
public static void main(String[] args) {
WithCondition<Integer> c = new WithCondition();
ReentrantLock lock = new ReentrantLock();
Condition condition = lock.newCondition();
new Thread(() -> {
System.out.println("t2启动");
lock.lock();
try {
if (c.size() != 5) {
try {
condition.await();
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("t2结束");
// 唤醒t1
condition.signal();
}
} finally {
lock.unlock();
}
}, "t2").start();
new Thread(() -> {
System.out.println("t1启动");
lock.lock();
try {
for (int i = 0; i < 10; i++) {
c.add(i);
System.out.println("add " + i);
if (c.size() == 5) {
// 唤醒t2
condition.signal();
try {
// 提前释放锁，让t2执行，否则需要等到t1的所有代码执行完才会释放锁
condition.await();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
} finally {
lock.unlock();
}
}, "t1").start();
}
}
CountDownLatch
public class WithCountDownLatch<E> {
List<E> list = new ArrayList();
public void add(E e) {
list.add(e);
}
public int size() {
return list.size();
}
public static void main(String[] args) {
WithCountDownLatch<Object> c = new WithCountDownLatch<>();
CountDownLatch latch1 = new CountDownLatch(1);
CountDownLatch latch2 = new CountDownLatch(1);
new Thread(() -> {
System.out.println("t2启动");
// 一开始就先拴住t2
try {
latch2.await();
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("t2结束");
// t2结束以后唤醒t1
latch1.countDown();
}, "t2").start();
new Thread(() -> {
System.out.println("t1启动");
for (int i = 0; i < 10; i++) {
c.add(i);
System.out.println("add " + i);
if (c.size() == 5) {
try {
// 先唤醒t2
latch2.countDown();
// 然后拴住t1自己
latch1.await();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}, "t1").start();
}
}
LockSupport
public class WithLockSupport<E> {
List<E> list = new ArrayList();
public void add(E e) {
list.add(e);
}
public int size() {
return list.size();
}
static Thread t1 = null, t2 = null;
public static void main(String[] args) {
WithLockSupport<Integer> c = new WithLockSupport<>();
t1 = new Thread(() -> {
System.out.println("t1启动");
for (int i = 0; i < 10; i++) {
c.add(i);
System.out.println("add " + i);
if (c.size() == 5) {
// 先唤醒t2
LockSupport.unpark(t2);
// 然后阻塞t1自己
LockSupport.park();
}
}
}, "t1");
t2 = new Thread(() -> {
System.out.println("t2启动");
// 阻塞t2自己
LockSupport.park();
System.out.println("t2结束");
// t2结束以后唤醒t1
LockSupport.unpark(t1);
}, "t2");
t2.start();
t1.start();
}
}
本文使用 mdnice 排版
