关于Deadlock的例子

发生Deadlock的情况&＃xff1a;

public class TestDeadlockExample1 { public static void main(String[] args) { final String resource1 &＃61; "ratan jaiswal"; final String resource2 &＃61; "vimal jaiswal"; // t1 tries to lock resource1 then resource2 Thread t1 &＃61; new Thread() { public void run() { synchronized (resource1) { System.out.println("Thread 1: locked resource 1"); try { Thread.sleep(100);} catch (Exception e) {} synchronized (resource2) { System.out.println("Thread 1: locked resource 2"); } } } }; // t2 tries to lock resource2 then resource1 Thread t2 &＃61; new Thread() { public void run() { synchronized (resource2) { System.out.println("Thread 2: locked resource 2"); try { Thread.sleep(100);} catch (Exception e) {} synchronized (resource1) { System.out.println("Thread 2: locked resource 1"); } } } }; t1.start(); t2.start(); }
}

输出结果&＃xff1a;

Thread 1: locked resource 1
Thread 2: locked resource 2

叙述&＃xff1a;发生了死锁。Thread1先获得resource1的lock&＃xff0c;Thread2先获得resource2的lock。在Thread1还没有将resource1的lock交出时&＃xff0c;又等着去获得resource2的lock&＃xff08;因为关于resource2的语句嵌套在关于resource1的语句中&＃xff09;&＃xff1b;同样&＃xff0c;在Thread2还没有将resource2的lock交出时&＃xff0c;又等着去获得resource1的lock&＃xff08;因为关于resource1的语句嵌套在关于resource2的语句中&＃xff09;。因此陷入了Deadlock

如果这样做&＃xff0c;就不会发生Deadlock了&＃xff1a;
&＃xff08;此代码并不是预防死锁的代码&＃xff0c;只是上面的一个例子的对照&＃xff09;

public class TestDeadLockExample1 { public static void main(String[] args) { final String resource1 &＃61; "ratan jaiswal"; final String resource2 &＃61; "vimal jaiswal"; // t1 tries to lock resource1 then resource2 Thread t1 &＃61; new Thread() { public void run() { synchronized (resource1) { System.out.println("Thread 1: locked resource 1"); try { Thread.sleep(100);} catch (Exception e) {} }synchronized (resource2) { System.out.println("Thread 1: locked resource 2"); } } }; // t2 tries to lock resource2 then resource1 Thread t2 &＃61; new Thread() { public void run() { synchronized (resource2) { System.out.println("Thread 2: locked resource 2"); try { Thread.sleep(100);} catch (Exception e) {} }synchronized (resource1) { System.out.println("Thread 2: locked resource 1"); } } }; t1.start(); t2.start(); } }


输出结果&＃xff1a;

Thread 1: locked resource 1
Thread 2: locked resource 2
Thread 2: locked resource 1
Thread 1: locked resource 2

此时&＃xff0c;获得lock1的前提并不是获得lock2了。