1、我們先驗證下wait可以用notify和notifyAll來喚醒
如下測試代碼：
public class WaitSleepDemo {
public static void main(String[] args) {
final Object lock = new Object();
new Thread(new Runnable() {
@Override
public void run() {
System.out.println("thread A is waiting to get lock");
synchronized (lock){
try {
System.out.println("thread A get lock");
Thread.sleep(20);
System.out.println("thread A do wait method");
//無限期的等待
lock.wait();
//Thread.sleep(1000);
System.out.println("thread A is done");
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}).start();
//為了讓Thread A 先於Thread B執行
try {
Thread.sleep(10);
} catch (InterruptedException e) {
e.printStackTrace();
}
new Thread(new Runnable() {
@Override
public void run() {
System.out.println("thread B is waiting to get lock");
synchronized (lock){
try {
System.out.println("thread B get lock");
System.out.println("thread B is sleeping 10 ms");
Thread.sleep(10);
// lock.wait(10);
System.out.println("thread B is done");
//這句注釋掉，thread A is done就不會被打印
lock.notify(); // lock.notifyAll();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}).start();
}
}
執行結果：
thread A is waiting to get lock thread A get lock thread B is waiting to get lock thread A do wait method thread B get lock thread B is sleeping 10 ms thread B is done thread A is done
2、notify和notifAll的區別
兩個概念
鎖池EntryList
等待池 WaitSet
鎖池：
假設線程A已經擁有了某個對象（不是類）的鎖，而其它線程B,C想要調用這個對象的某個某個synchronized方法(或者塊)之前必須獲得該對象鎖的擁有權，而恰巧該對象的鎖目前正被A所占有，此時B， C線程就會被阻塞，進入一個地方去等待鎖的釋放，這個地方便是該對象的鎖池。
等待池
假設線程A調用了某個對象的wait方法，線程A就會釋放該對象的鎖，同時線程A就進入到了該對象的等待池中，進入等待池中的線程不會去競爭該對象的鎖。
notify和notifAll的區別
notifyAll： 會讓所有處於等待池的線程全部進入鎖池去競爭獲取鎖的機會
notify： 只會隨機選取一個處於等待池中的線程進入鎖池去競爭獲取鎖的機會。
如下的測試代碼
public class NotificationDemo {
private volatile boolean go = false;
private synchronized void shouldGo() throws InterruptedException {
while (go != true){
System.out.println(Thread.currentThread() + " is going to wait on this object");
wait();
System.out.println(Thread.currentThread() + " is woken up");
}
go = false; //reseting condition
}
private synchronized void go() throws InterruptedException {
while (go == false){
System.out.println(Thread.currentThread() + " is going to notify all or one ");
go = true;
notify();
}
}
public static void main(String[] args) throws InterruptedException {
NotificationDemo test = new NotificationDemo();
Runnable waitTak = new Runnable() {
@Override
public void run() {
try {
test.shouldGo();
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName() + " finish execution");
}
};
Runnable notifyTask = new Runnable() {
@Override
public void run() {
try {
test.go();
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName() + " finish execution");
}
};
Thread t1 = new Thread(waitTak, "WT1");
Thread t2 = new Thread(waitTak, "WT2");
Thread t3 = new Thread(waitTak, "WT3");
t1.start();
t2.start();
t3.start();
Thread t4 = new Thread(notifyTask, "NT1");
Thread.sleep(200);
t4.start();
}
}
打印結果：
Thread[WT1,5,main] is going to wait on this object Thread[WT2,5,main] is going to wait on this object Thread[WT3,5,main] is going to wait on this object Thread[NT1,5,main] is going to notify all or one Thread[WT1,5,main] is woken up NT1 finish execution WT1 finish execution
多執行幾次，可以發現notify調用后，被喚醒的線程是隨機的。
將notify改成notifyAll
打印結果如下：
Thread[WT1,5,main] is going to wait on this object Thread[WT3,5,main] is going to wait on this object Thread[WT2,5,main] is going to wait on this object Thread[NT1,5,main] is going to notify all or one Thread[WT2,5,main] is woken up Thread[WT3,5,main] is woken up Thread[WT3,5,main] is going to wait on this object NT1 finish execution Thread[WT1,5,main] is woken up Thread[WT1,5,main] is going to wait on this object WT2 finish execution
說明三個線程都被喚醒了