示例：
public class DeadLock {
public static void main(String[] args) {
A a = new A();
B b = new B();
new Thread(new Runnable() {
@Override
public void run() {
synchronized (b) {
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
synchronized (a) {
System.out.println("b lock before a");
}
}
}
}).start();
new Thread(new Runnable() {
@Override
public void run() {
synchronized (a) {
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
synchronized (b) {
}
}
}
}).start();
}
static class A{
}
static class B{
}
}
运行后通过java visualvm 看到检测到死锁：
Found one Java-level deadlock:
=============================
"Thread-1":
waiting to lock monitor 0x0000000002a4e728 (object 0x00000007809cb220, a com.thread.threadlocal.DeadLock$B),
which is held by "Thread-0"
"Thread-0":
waiting to lock monitor 0x0000000002a4d288 (object 0x00000007809c9eb0, a com.thread.threadlocal.DeadLock$A),
which is held by "Thread-1"
Java stack information for the threads listed above:
===================================================
"Thread-1":
at com.thread.threadlocal.DeadLock$2.run(DeadLock.java:36)
- waiting to lock <0x00000007809cb220> (a com.thread.threadlocal.DeadLock$B)
- locked <0x00000007809c9eb0> (a com.thread.threadlocal.DeadLock$A)
at java.lang.Thread.run(Thread.java:748)
"Thread-0":
at com.thread.threadlocal.DeadLock$1.run(DeadLock.java:20)
- waiting to lock <0x00000007809c9eb0> (a com.thread.threadlocal.DeadLock$A)
- locked <0x00000007809cb220> (a com.thread.threadlocal.DeadLock$B)
at java.lang.Thread.run(Thread.java:748)
Found 1 deadlock.
线程死锁出现的四个条件：
上面示例就是其中一种互相等待对方释放锁的情况，下述博文详细介绍了死锁产生的原因以及避免死锁发生：
https://blog.csdn.net/jyy305/article/details/70077042
https://blog.csdn.net/ls5718/article/details/51896159
