我是多线程的新手,我遇到了这个例子：

public class TestThread {

public static Object Lock1 = new Object();

public static Object Lock2 = new Object();

public static void main(String args[]) {

ThreadDemo1 T1 = new ThreadDemo1();

ThreadDemo2 T2 = new ThreadDemo2();

T1.start();

T2.start();

}

private static class ThreadDemo1 extends Thread {

public void run() {

synchronized (Lock1) {

System.out.println("Thread 1: Holding lock 1...");

try { Thread.sleep(10); }

catch (InterruptedException e) {}

System.out.println("Thread 1: Waiting for lock 2...");

synchronized (Lock2) {

System.out.println("Thread 1: Holding lock 1 & 2...");

}

}

}

}

private static class ThreadDemo2 extends Thread {

public void run() {

synchronized (Lock2) {

System.out.println("Thread 2: Holding lock 2...");

try { Thread.sleep(10); }

catch (InterruptedException e) {}

System.out.println("Thread 2: Waiting for lock 1...");

synchronized (Lock1) {

System.out.println("Thread 2: Holding lock 1 & 2...");

}

}

}

}

}

这会导致以下示例输出：

Thread 1: Holding lock 1...

Thread 2: Holding lock 2...

Thread 1: Waiting for lock 2...

Thread 2: Waiting for lock 1...

即,存在僵局.但是,如果我们改变在第二个线程中获得的锁的顺序,那么它现在看起来像这样：

public class TestThread {

public static Object Lock1 = new Object();

public static Object Lock2 = new Object();

public static void main(String args[]) {

ThreadDemo1 T1 = new ThreadDemo1();

ThreadDemo2 T2 = new ThreadDemo2();

T1.start();

T2.start();

}

private static class ThreadDemo1 extends Thread {

public void run() {

synchronized (Lock1) {

System.out.println("Thread 1: Holding lock 1...");

try { Thread.sleep(10); }

catch (InterruptedException e) {}

System.out.println("Thread 1: Waiting for lock 2...");

synchronized (Lock2) {

System.out.println("Thread 1: Holding lock 1 & 2...");

}

}

}

}

private static class ThreadDemo2 extends Thread {

public void run() {

synchronized (Lock1) {

System.out.println("Thread 2: Holding lock 1...");

try { Thread.sleep(10); }

catch (InterruptedException e) {}

System.out.println("Thread 2: Waiting for lock 2...");

synchronized (Lock2) {

System.out.println("Thread 2: Holding lock 1 & 2...");

}

}

}

}

}

它按预期工作,示例输出如下所示：

Thread 1: Holding lock 1...

Thread 1: Waiting for lock 2...

Thread 1: Holding lock 1 & 2...

Thread 2: Holding lock 1...

Thread 2: Waiting for lock 2...

Thread 2: Holding lock 1 & 2...

有人可以向我解释第一个导致死锁的情况,以及为什么第二个代码的更改会修复它？