一.問題當主線程調用子線程的join方法時，其實還是調用子線程的wait方法來阻塞主線程，那么有兩個問題：a.如果我在另一個子線程中獲得當前子線程對象，并調用線程的notify方法，是不是可以解除子線程的阻塞，經(jīng)測試會報監(jiān)視器狀態(tài)異常。b.子線程是個單獨的對象，為啥會阻塞主線程呢？又不存在共享資源競爭，尤其是Thread中join方法是個普通的synchronized方法二、代碼public class JoinTest {public static void main(String[] args) throws InterruptedException { MyThread3 thread=new MyThread3(); NotifyThread nt=new NotifyThread(thread); thread.start(); nt.start(); thread.join(); for(int i=0;i<3;i++){ System.out.println(Thread.currentThread().getName() + "線程第" + i + "次執(zhí)行！"); }}}class NotifyThread extends Thread{Thread myThread ;public NotifyThread(Thread myThread){ this.myThread=myThread;}public void run(){ try { System.out.println("休眠開始"); Thread.sleep(3000); System.out.println("休眠結束"); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } myThread.notify(); System.out.println("已喚醒，讓Join失效");}}class MyThread3 extends Thread {@Overridepublic void run() { for (int i = 0; i < 10; i++) { try { System.out.println(this.getName() + "線程第" + i + "次執(zhí)行！"); Thread.sleep(1000); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } }}三、異常Thread-0線程第0次執(zhí)行！休眠開始Thread-0線程第1次執(zhí)行！Thread-0線程第2次執(zhí)行！休眠結束Exception in thread "Thread-1" java.lang.IllegalMonitorStateExceptionat java.lang.Object.notify(Native Method)at thread.com.simple.NotifyThread.run(JoinTest.java:29)Thread-0線程第3次執(zhí)行！Thread-0線程第4次執(zhí)行！Thread-0線程第5次執(zhí)行！Thread-0線程第6次執(zhí)行！Thread-0線程第7次執(zhí)行！Thread-0線程第8次執(zhí)行！Thread-0線程第9次執(zhí)行！main線程第0次執(zhí)行！main線程第1次執(zhí)行！main線程第2次執(zhí)行！
1 回答
湖上湖
TA貢獻2003條經(jīng)驗 獲得超2個贊
先談為什么“喚醒”不了，notify不會“喚醒”MyThread3，因為阻塞不就是join方法的使命么？再說MyThread3也沒有休眠，不是一直在執(zhí)行么，何來“喚醒”之說！
最后來看看join方法的實現(xiàn)，或許對你理解有幫助：
public final synchronized void join(long millis) throws InterruptedException {
long base = System.currentTimeMillis();
long now = 0;
if (millis < 0) {
throw new IllegalArgumentException("timeout value is negative");
}
if (millis == 0) {
while (isAlive()) {
wait(0);
}
} else {
while (isAlive()) {
long delay = millis - now;
if (delay <= 0) {
break;
}
wait(delay);
now = System.currentTimeMillis() - base;
}
}
}
再來談為什么有異常，其實已經(jīng)比較明確了，看注釋：
/**
* Thrown to indicate that a thread has attempted to wait on an
* object's monitor or to notify other threads waiting on an object's
* monitor without owning the specified monitor.
*/
當前線程不是該對象monitor所有者時，試圖調用其wait或者notify方法就會報這個錯，解決異常只要拿到所有者就好了，常見方法：
public class NotifyThread extends Thread{
Thread myThread ;
public NotifyThread(Thread myThread){
this.myThread=myThread;
}
public void run(){
try {
System.out.println("休眠開始");
Thread.sleep(3000);
System.out.println("休眠結束");
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
synchronized(myThread){
myThread.notify();
}
System.out.println("已喚醒，讓Join失效");
}
}
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