JavaThread多线程开发中Object类详细讲解
方法概览
Thread
wait notify notifyAll方法详解
作用
阻塞阶段
使用了wait方法之后，线程就会进入阻塞阶段，只有发生以下四种情况中的其中一个，线程才会被唤醒
- 另一个线程调用了这个线程的notify方法，刚好唤醒的是本线程
- 另一个线程调用了这个对象的notifyAll方法
- 过了wait规定的超时时间
- 线程调用了interrupt
唤醒阶段
notify会唤醒单个处于阻塞状态的线程，唤醒的线程是随机的
notify和wait都需要写在synchronized代码块里，不然会抛出异常
notifyAll会唤醒所有等待的线程
遇到中断
执行wait方法之后，被中断，会抛出InterruptedException这个异常
代码展示
- 展示wait和notify的基本用法
- 该代码执行wait方法之后会释放锁，然后thread2执行notify方法
- notify方法执行完毕之后，并没有立即释放锁，而是接着执行之后的代码,也就是打印“Thread2调用notify”这句话
- thread2执行完毕之后，会进行释放锁，thread1才会继续执行
- 在此期间，thread1虽然被唤醒，但是一直在等待thread2同步代码块里面的代码执行完毕
public class Wait {
public static void main(String[] args) throws InterruptedException {
Thread1 thread1 = new Thread1();
Thread2 thread2 = new Thread2();
thread1.start();
Thread.sleep(200);
thread2.start();
}
public static Object object = new Object();
static class Thread1 extends Thread {
@Override
public void run() {
synchronized (object) {
System.out.println("Thread1执行");
try {
object.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("Thread1获取锁");
}
}
}
static class Thread2 extends Thread {
@Override
public void run() {
synchronized (object) {
object.notify();
System.out.println("Thread2调用notify");
}
}
}
}
- notify和notifyAll的展示
- 第一个输出：threadc调用notifyAll
- 第二个输出：threadc调用notify
- 调用notify的时候，程序并没有结束，threadb陷入等待
public class notifyOrAll implements Runnable{
private static final Object a = new Object();
public static void main(String[] args) throws InterruptedException {
Runnable r = new notifyOrAll();
Thread threada = new Thread(r);
Thread threadb = new Thread(r);
Thread threadc = new Thread(new Runnable() {
@Override
public void run() {
synchronized (a) {
// a.notifyAll();
a.notify();
System.out.println(Thread.currentThread().getName() + "notify");
}
}
});
threada.start();
Thread.sleep(200);
threadb.start();
Thread.sleep(200);
threadc.start();
}
@Override
public void run() {
synchronized (a) {
System.out.println(Thread.currentThread().getName() + "得到锁");
try {
System.out.println(Thread.currentThread().getName() + "wait");
a.wait();
System.out.println(Thread.currentThread().getName() + "wait结束");
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
- 只释放当前monitor
- 证明wait只释放当前的那把锁
public class OwnMonitor {
private static volatile Object a = new Object();
private static volatile Object b = new Object();
public static void main(String[] args) throws InterruptedException {
Thread threadA = new Thread(new Runnable() {
@Override
public void run() {
synchronized (a) {
System.out.println("threadA得到a");
synchronized (b) {
System.out.println("threadA得到锁b");
try {
System.out.println("threadA释放a");
a.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
});
Thread threadB = new Thread(new Runnable() {
@Override
public void run() {
synchronized (a) {
System.out.println("threadB得到a");
System.out.println("threadB要获取b");
synchronized (b) {
System.out.println("threadB得到b");
}
}
}
});
threadA.start();
Thread.sleep(1000);
threadB.start();
}
}
特点
- 执行这些方法必须先获取锁
- notify只能换取一个，而且是随机的
- 都属于Object。任何对象都可以调用
- 都是native final修饰的
当线程从wait状态刚被唤醒时，通常不能直接得到锁，那就会从waiting状态转换到blocked状态，抢到锁之后状态转变为runnable
如果发生异常，则直接跳到Terminated状态
通过wait notify方法实现生产者和消费者
- 将storge当作生产者和消费者进行工作的仓库
- 如果storge中没有数据，生产者就开始wait
- 如果storge中数据满了，消费者就开始wait
- 生产者和消费者每进行一次生产和消费，就执行notify
public class ProducerConsumer {
public static void main(String[] args) {
Storge storge = new Storge();
Producer producer = new Producer(storge);
Consumer consumer = new Consumer(storge);
new Thread(producer).start();
new Thread(consumer).start();
}
}
class Producer implements Runnable {
private Storge storge;
public Producer(Storge storge) {
this.storge = storge;
}
@Override
public void run() {
for (int i = 0; i < 100; i++) {
storge.put();
}
}
}
class Consumer implements Runnable {
private Storge storge;
public Consumer(Storge storge) {
this.storge = storge;
}
@Override
public void run() {
for (int i = 0; i < 100; i++) {
storge.take();
}
}
}
class Storge {
private int maxSize;
private LinkedList<Date> storge;
public Storge() {
maxSize = 10;
storge = new LinkedList<>();
}
public synchronized void put() {
while (storge.size() == maxSize) {
try {
wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
storge.add(new Date());
System.out.println("已经有了" + storge.size());
notify();
}
public synchronized void take() {
while (storge.size() == 0) {
try {
wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
System.out.println("拿到了" + storge.poll() + "还剩" + storge.size());
notify();
}
}
sleep方法详解
作用：让线程在预期的时间执行，其他时间不占用CPU资源
特点：和wait不一样，sleep不释放锁
sleep不会释放锁
证明sleep不会释放 synchronized锁
public class SleepSyn implements Runnable{
public static void main(String[] args) {
SleepSyn sleepSyn = new SleepSyn();
new Thread(sleepSyn).start();
new Thread(sleepSyn).start();
}
@Override
public void run() {
syn();
}
private synchronized void syn() {
System.out.println(Thread.currentThread().getName() + "获取锁");
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName() + "释放锁");
}
}
证明sleep不释放Lock锁
public class sleepLock implements Runnable{
private static final Lock LOCK = new ReentrantLock();
@Override
public void run() {
LOCK.lock();
System.out.println(Thread.currentThread().getName() + "获取锁");
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
LOCK.unlock();
}
System.out.println(Thread.currentThread().getName() + "释放锁");
}
public static void main(String[] args) {
sleepLock sleepLock = new sleepLock();
new Thread(sleepLock).start();
new Thread(sleepLock).start();
}
}
sleep响应中断
- 抛出InterruptedException
- 会清除中断状态
- 中断之后，抛出异常继续执行
public class sleepInterrupted implements Runnable{
public static void main(String[] args) throws InterruptedException {
Thread thread = new Thread(new sleepInterrupted());
thread.start();
Thread.sleep(2000);
thread.interrupt();
}
@Override
public void run() {
for (int i = 0; i < 10; i++) {
System.out.println(new Date());
try {
TimeUnit.SECONDS.sleep(1);
} catch (InterruptedException e) {
System.out.println("中断");
e.printStackTrace();
}
}
}
}
总结
sleep方法可以让线程进入waiting状态，不占用CPU资源，但是不释放锁，规定时间之后再运行
休眠期间如果被打断，会抛出异常并清除中断状态
join方法详解
新线程加入，主线程等子线程执行完毕
代码展示
- 前一个结果是使用join
- 后一个结果是没使用join
- 可知使用join之后，主线程会等join的线程执行完毕再继续执行
public class join {
public static void main(String[] args) throws InterruptedException {
Thread thread1 = new Thread(new Runnable() {
@Override
public void run() {
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName() + "执行完毕");
}
});
Thread thread2 = new Thread(new Runnable() {
@Override
public void run() {
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName() + "执行完毕");
}
});
thread1.start();
thread2.start();
System.out.println("开始等待子线程运行");
// thread1.join();
// thread2.join();
System.out.println("所有线程执行完毕");
}
}
- 遇到中断
- 第一个的运行结果是主线程没中断的打印结果
- 第二个的运行结果是join期间进行中断的打印结果，可知在打印了“子线程运行完毕”之后，依然打印了“启动”两个字，可知会造成运行混乱
- 可以在捕获异常的代码块中，将join的线程也中断，可以解决上面的问题
public class joinInterrupt {
public static void main(String[] args) {
Thread main1 = Thread.currentThread();
Thread thread1 = new Thread(new Runnable() {
@Override
public void run() {
try {
main1.interrupt();
Thread.sleep(2000);
System.out.println("启动");
} catch (InterruptedException e) {
e.printStackTrace();
}
}
});
thread1.start();
System.out.println("join");
try {
thread1.join();
} catch (InterruptedException e) {
System.out.println(Thread.currentThread().getName() + "中断");
// thread1.interrupt();
e.printStackTrace();
}
System.out.println("子线程运行完毕");
}
}
join期间，线程处于WAITING状态
public class joinStates {
public static void main(String[] args) throws InterruptedException {
Thread main1 = Thread.currentThread();
Thread thread = new Thread(new Runnable() {
@Override
public void run() {
try {
Thread.sleep(3000);
System.out.println(main1.getState());
System.out.println("子线程运行结束");
} catch (InterruptedException e) {
e.printStackTrace();
}
}
});
thread.start();
System.out.println("join");
thread.join();
System.out.println("运行完毕");
}
}
yield方法
用来释放CPU时间片，但是不一定能达到预期的效果，因为有时CPU资源不紧张，无需yield
和sleep的区别是：sleep期间不会被再次调度但是yield会立刻处于竞争状态，还会随时再次被调度
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