标签：current dex thread red and new clear ace net
wait(), notify()和notifyAll()方法用于在线程间建立关联. 在对象上调用wait()将使线程进入WAITTING状态, 直到其他线程对同一个对象调用notify()或notifyAll(). 在任何线程上, 对一个对象调用wait(), notify()和notifyAll(), 都需要先获得这个对象的锁, 就是说, 这些方法必须在synchronized方法或代码块中调用.
调用notify()时, 在所有WAITING状态的线程中只会有一个线程被通知, 这个选择是随机的, 被通知的线程并不会立即得到对象的锁, 而是一直等到调用notify()的线程释放锁, 在这之前线程都是BLOCKED状态. 当获得锁后, 就会从BLOCKED状态变为RUNNING状态. 例子
class Shared {
synchronized void waitMethod() {
Thread t = Thread.currentThread();
System.out.println(t.getName() + " is releasing the lock and going to wait");
try {
wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(t.getName() + " has been notified and acquired the lock back");
}
synchronized void notifyOneThread() {
Thread t = Thread.currentThread();
notify();
System.out.println(t.getName() + " has notified one thread waiting for this object lock");
}
}
public class MainClass {
public static void main(String[] args) {
final Shared s = new Shared();
//Thread t1 will be waiting for lock of object ‘s‘
Thread t1 = new Thread() {
@Override
public void run() {
s.waitMethod();
}
};
t1.start();
//Thread t2 will be waiting for lock of object ‘s‘
Thread t2 = new Thread() {
@Override
public void run() {
s.waitMethod();
}
};
t2.start();
//Thread t3 will be waiting for lock of object ‘s‘
Thread t3 = new Thread() {
@Override
public void run() {
s.waitMethod();
}
};
t3.start();
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
//Thread t4 will notify only one thread which is waiting for lock of object ‘s‘
Thread t4 = new Thread() {
@Override
public void run() {
s.notifyOneThread();
}
};
t4.start();
}
}
.
当线程在对象上调用notifyAll()时, 所有WAITING状态的线程都会被通知, 所有的线程都会从WAITING状态变成BLOCKED状态, 然后争抢对象的锁. 得到对象锁的线程, 将变成RUNNING状态, 而其他线程则继续保持BLOCKED状态继续等待获取对象锁. 例子
class Shared {
synchronized void waitMethod() {
Thread t = Thread.currentThread();
System.out.println(t.getName() + " is releasing the lock and going to wait");
try {
wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(t.getName() + " has been notified and acquired the lock back");
}
synchronized void notifyAllThread() {
Thread t = Thread.currentThread();
notifyAll();
System.out.println(t.getName() + " has notified all threads waiting for this object lock");
}
}
public class MainClass {
public static void main(String[] args) {
final Shared s = new Shared();
//Thread t1 will be waiting for lock of object ‘s‘
Thread t1 = new Thread() {
@Override
public void run() {
s.waitMethod();
}
};
t1.start();
//Thread t2 will be waiting for lock of object ‘s‘
Thread t2 = new Thread() {
@Override
public void run() {
s.waitMethod();
}
};
t2.start();
//Thread t3 will be waiting for lock of object ‘s‘
Thread t3 = new Thread() {
@Override
public void run() {
s.waitMethod();
}
};
t3.start();
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
//Thread t4 will notify all threads which are waiting for lock of object ‘s‘
Thread t4 = new Thread() {
@Override
public void run() {
s.notifyAllThread();
}
};
t4.start();
}
}
.
一个生产者和消费者的例子
注意, 在1个生产1个消费的情况下, 是能确保生产和消费的互相通知的, 但是在2个生产1个消费的情况下, 有可能要多次notify后消费线程才能拿到queue的锁.
public class DemoThreadWait1 {
Queue<Integer> queue = new LinkedList<>();
public void consume() {
synchronized (queue) {
while (queue.isEmpty()) {
try {
System.out.println("consume wait");
queue.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("remove all");
queue.clear();
queue.notify();
}
}
}
public void produce(int i) {
synchronized (queue) {
if (queue.size() < 5) {
System.out.println("add " + i);
queue.add(i);
}
if (queue.size() >= 5) {
queue.notify();
try {
System.out.println("produce wait");
queue.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
public static void main(String[] args) {
DemoThreadWait1 demo = new DemoThreadWait1();
new Thread(()->{
while(true) {
demo.consume();
}
}).start();
new Thread(()->{
while(true) {
demo.produce((int) (Math.random() * 1000));
}
}).start();
new Thread(()->{
while(true) {
demo.produce((int) (Math.random() * 1000));
}
}).start();
}
}
Java线程的wait(), notify()和notifyAll()
标签：current dex thread red and new clear ace net
原文地址：https://www.cnblogs.com/milton/p/10884427.html
