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Java jstack 命令详解
Java 中 jstack 命令可以用来查看运行的 Java 进程下，多线程的运行情况，我们用一个死锁的例子来看：
比如下面这段死锁的代码：
public class DeadLock {
private static Object objA = new Object);
private static Object objB = new Object);
public static void mainString[] args) {
Thread thread1 = new Threadnew Thread1));
Thread thread2 = new Threadnew Thread2));
thread1.start);
thread2.start);
}
private static class Thread1 implements Runnable{
@Override
public void run) {
synchronized objA) {
System.out.println"线程1得到A对象的锁");
try {
Thread.sleep3000);
} catch InterruptedException e) {
e.printStackTrace);
}
synchronized objB) {
System.out.println"线程1得到B对象的锁");
}
}
}
}
private static class Thread2 implements Runnable{
@Override
public void run) {
synchronized objB) {
System.out.println"线程2得到B对象的锁");
try {
Thread.sleep3000);
} catch InterruptedException e) {
e.printStackTrace);
}
synchronized objA) {
System.out.println"线程2得到A对象的锁");
}
}
}
}
}
当然，运行结果只能看到两个线程只拿到了一个锁，在一直等待对方的锁。
线程1得到A对象的锁 线程2得到B对象的锁
我们可以使用 jps 来查看对应的 PID ，然后使用 jstack 来查看其线程情况：
[root@admin ~]# jps 42576 Jps 43616 DeadLock
[root@admin ~]# jstack 43616
Full thread dump Java HotSpotTM) 64-Bit Server VM 24.45-b08 mixed mode):
"DestroyJavaVM" prio=6 tid=0x00000000047c1000 nid=0x9878 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"Thread-1" prio=6 tid=0x0000000010aa3000 nid=0xafa0 waiting for monitor entry [0x000000001105f000]
java.lang.Thread.State: BLOCKED on object monitor)
at com.zaimeibian.Test$Thread2.runTest.java:46)
- waiting to lock <0x00000007c099cc20> a java.lang.Object)
- locked <0x00000007c099cc30> a java.lang.Object)
at java.lang.Thread.runThread.java:744)
"Thread-0" prio=6 tid=0x0000000010aa2800 nid=0xae74 waiting for monitor entry [0x0000000010f5f000]
java.lang.Thread.State: BLOCKED on object monitor)
at com.zaimeibian.Test$Thread1.runTest.java:27)
- waiting to lock <0x00000007c099cc30> a java.lang.Object)
- locked <0x00000007c099cc20> a java.lang.Object)
at java.lang.Thread.runThread.java:744)
"Service Thread" daemon prio=6 tid=0x000000000f10a000 nid=0x9a8c runnable [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"C2 CompilerThread1" daemon prio=10 tid=0x000000000f109800 nid=0xaf28 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"C2 CompilerThread0" daemon prio=10 tid=0x000000000f105800 nid=0x85dc waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"Attach Listener" daemon prio=10 tid=0x000000000f104800 nid=0xac04 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"Signal Dispatcher" daemon prio=10 tid=0x000000000f102000 nid=0xa678 runnable [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"Finalizer" daemon prio=8 tid=0x000000000f0bd000 nid=0xaed8 in Object.wait) [0x000000001045f000]
java.lang.Thread.State: WAITING on object monitor)
at java.lang.Object.waitNative Method)
- waiting on <0x00000007c0905568> a java.lang.ref.ReferenceQueue$Lock)
at java.lang.ref.ReferenceQueue.removeReferenceQueue.java:135)
- locked <0x00000007c0905568> a java.lang.ref.ReferenceQueue$Lock)
at java.lang.ref.ReferenceQueue.removeReferenceQueue.java:151)
at java.lang.ref.Finalizer$FinalizerThread.runFinalizer.java:189)
"Reference Handler" daemon prio=10 tid=0x000000000f0b2000 nid=0xaedc in Object.wait) [0x000000001035f000]
java.lang.Thread.State: WAITING on object monitor)
at java.lang.Object.waitNative Method)
- waiting on <0x00000007c09050f0> a java.lang.ref.Reference$Lock)
at java.lang.Object.waitObject.java:503)
at java.lang.ref.Reference$ReferenceHandler.runReference.java:133)
- locked <0x00000007c09050f0> a java.lang.ref.Reference$Lock)
"VM Thread" prio=10 tid=0x000000000f0b0000 nid=0xaef0 runnable
"GC task thread#0 ParallelGC)" prio=6 tid=0x00000000047d6000 nid=0xacb0 runnable
"GC task thread#1 ParallelGC)" prio=6 tid=0x00000000047d8000 nid=0xaee0 runnable
"GC task thread#2 ParallelGC)" prio=6 tid=0x00000000047d9800 nid=0xaed4 runnable
"GC task thread#3 ParallelGC)" prio=6 tid=0x00000000047db000 nid=0xac54 runnable
"VM Periodic Task Thread" prio=10 tid=0x000000000f132000 nid=0xaff0 waiting on condition
JNI global references: 105
Found one Java-level deadlock:
=============================
"Thread-1":
waiting to lock monitor 0x000000000f0ba488 object 0x00000007c099cc20, a java.lang.Object),
which is held by "Thread-0"
"Thread-0":
waiting to lock monitor 0x000000000f0bcf28 object 0x00000007c099cc30, a java.lang.Object),
which is held by "Thread-1"
Java stack information for the threads listed above:
===================================================
"Thread-1":
at com.zaimeibian.Test$Thread2.runTest.java:46)
- waiting to lock <0x00000007c099cc20> a java.lang.Object)
- locked <0x00000007c099cc30> a java.lang.Object)
at java.lang.Thread.runThread.java:744)
"Thread-0":
at com.zaimeibian.Test$Thread1.runTest.java:27)
- waiting to lock <0x00000007c099cc30> a java.lang.Object)
- locked <0x00000007c099cc20> a java.lang.Object)
at java.lang.Thread.runThread.java:744)
Found 1 deadlock.
我们可以看到 jstack 打印出了线程的状态，而且发现一个死锁。
另外，线程状态有以下几种：
– RUNNABLE 线程运行中或 I/O 等待
– BLOCKED 线程在等待 monitor 锁 synchronized 关键字)
– TIMED_WAITING 线程在等待唤醒，但设置了时限
– WAITING 线程在无限等待唤醒
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