线程死锁

原创转载请注明出处：https://agilestyle.iteye.com/blog/2440433

 

死锁：一组互相竞争资源的线程因互相等待，导致“永久”阻塞的现象。 

解决死锁，要么重启，要么规避

那如何避免死锁呢？要避免死锁就需要分析死锁发生的条件，只有以下这四个条件都发生时才会出现死锁：

 

1.互斥，共享资源 X 和 Y 只能被一个线程占用；

2.占有且等待，线程 T1 已经取得共享资源 X，在等待共享资源 Y 的时候，不释放共享资源 X；

3.不可抢占，其他线程不能强行抢占线程 T1 占有的资源；

4.循环等待，线程 T1 等待线程 T2 占有的资源，线程 T2 等待线程 T1 占有的资源，就是循环等待。

 

反过来分析，也就是说只要破坏其中一个，就可以成功避免死锁的发生。 

 

模拟一个死锁的程序

DeadLockTest.java

package org.fool.test;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class DeadLockTest {
    private static Lock lockA = new ReentrantLock();
    private static Lock lockB = new ReentrantLock();

    public static void main(String args[]) {
        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    lockA.lock();
                    System.out.println("=====Thread A outer invoked...=====");
                    TimeUnit.SECONDS.sleep(3);
                    try {
                        lockB.lock();
                        System.out.println("=====Thread A inner invoked...=====");
                    } finally {
                        lockB.unlock();
                    }
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } finally {
                    lockA.unlock();
                }
            }
        }, "Thread-A").start();

        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    lockB.lock();
                    System.out.println("=====Thread B outer invoked...=====");
                    TimeUnit.SECONDS.sleep(3);
                    try {
                        lockA.lock();
                        System.out.println("=====Thread B inner invoked...=====");
                    } finally {
                        lockA.unlock();
                    }
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } finally {
                    lockB.unlock();
                }
            }
        }, "Thread-B").start();
    }
}

 

打包成可执行jar包后，运行java -jar hello-deadlock-1.0-SNAPSHOT.jar

 

ps -ef | grep java 找出对应的pid，使用jstack打出堆栈信息

2019-04-25 15:49:30
Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.121-b13 mixed mode):

"Attach Listener" #13 daemon prio=9 os_prio=31 tid=0x00007fb881058800 nid=0x1407 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"DestroyJavaVM" #12 prio=5 os_prio=31 tid=0x00007fb882802000 nid=0x1c03 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"Thread-B" #11 prio=5 os_prio=31 tid=0x00007fb883807000 nid=0x5903 waiting on condition [0x0000700002f89000]
   java.lang.Thread.State: WAITING (parking)
	at sun.misc.Unsafe.park(Native Method)
	- parking to wait for  <0x000000076abdaa00> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)
	at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
	at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:836)
	at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(AbstractQueuedSynchronizer.java:870)
	at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:1199)
	at java.util.concurrent.locks.ReentrantLock$NonfairSync.lock(ReentrantLock.java:209)
	at java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:285)
	at org.fool.test.DeadLockTest$2.run(DeadLockTest.java:41)
	at java.lang.Thread.run(Thread.java:745)

"Thread-A" #10 prio=5 os_prio=31 tid=0x00007fb8800a7800 nid=0x5703 waiting on condition [0x0000700002e86000]
   java.lang.Thread.State: WAITING (parking)
	at sun.misc.Unsafe.park(Native Method)
	- parking to wait for  <0x000000076abdaa30> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)
	at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
	at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:836)
	at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(AbstractQueuedSynchronizer.java:870)
	at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:1199)
	at java.util.concurrent.locks.ReentrantLock$NonfairSync.lock(ReentrantLock.java:209)
	at java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:285)
	at org.fool.test.DeadLockTest$1.run(DeadLockTest.java:20)
	at java.lang.Thread.run(Thread.java:745)

"Service Thread" #9 daemon prio=9 os_prio=31 tid=0x00007fb882051000 nid=0x5303 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"C1 CompilerThread3" #8 daemon prio=9 os_prio=31 tid=0x00007fb880009800 nid=0x5103 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"C2 CompilerThread2" #7 daemon prio=9 os_prio=31 tid=0x00007fb881044000 nid=0x4f03 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"C2 CompilerThread1" #6 daemon prio=9 os_prio=31 tid=0x00007fb881043000 nid=0x4d03 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"C2 CompilerThread0" #5 daemon prio=9 os_prio=31 tid=0x00007fb882025800 nid=0x4b03 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"Signal Dispatcher" #4 daemon prio=9 os_prio=31 tid=0x00007fb88200c800 nid=0x4903 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"Finalizer" #3 daemon prio=8 os_prio=31 tid=0x00007fb880858000 nid=0x3903 in Object.wait() [0x000070000266e000]
   java.lang.Thread.State: WAITING (on object monitor)
	at java.lang.Object.wait(Native Method)
	- waiting on <0x000000076ab08ec8> (a java.lang.ref.ReferenceQueue$Lock)
	at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:143)
	- locked <0x000000076ab08ec8> (a java.lang.ref.ReferenceQueue$Lock)
	at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:164)
	at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:209)

"Reference Handler" #2 daemon prio=10 os_prio=31 tid=0x00007fb880855800 nid=0x3703 in Object.wait() [0x000070000256b000]
   java.lang.Thread.State: WAITING (on object monitor)
	at java.lang.Object.wait(Native Method)
	- waiting on <0x000000076ab06b68> (a java.lang.ref.Reference$Lock)
	at java.lang.Object.wait(Object.java:502)
	at java.lang.ref.Reference.tryHandlePending(Reference.java:191)
	- locked <0x000000076ab06b68> (a java.lang.ref.Reference$Lock)
	at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:153)

"VM Thread" os_prio=31 tid=0x00007fb881002800 nid=0x3503 runnable

"GC task thread#0 (ParallelGC)" os_prio=31 tid=0x00007fb880014800 nid=0x2503 runnable

"GC task thread#1 (ParallelGC)" os_prio=31 tid=0x00007fb880015800 nid=0x2703 runnable

"GC task thread#2 (ParallelGC)" os_prio=31 tid=0x00007fb880016000 nid=0x2903 runnable

"GC task thread#3 (ParallelGC)" os_prio=31 tid=0x00007fb880016800 nid=0x2b03 runnable

"GC task thread#4 (ParallelGC)" os_prio=31 tid=0x00007fb881001000 nid=0x2d03 runnable

"GC task thread#5 (ParallelGC)" os_prio=31 tid=0x00007fb881002000 nid=0x2f03 runnable

"GC task thread#6 (ParallelGC)" os_prio=31 tid=0x00007fb880800800 nid=0x3103 runnable

"GC task thread#7 (ParallelGC)" os_prio=31 tid=0x00007fb880801000 nid=0x3303 runnable

"VM Periodic Task Thread" os_prio=31 tid=0x00007fb880828800 nid=0x5503 waiting on condition

JNI global references: 6


Found one Java-level deadlock:
=============================
"Thread-B":
  waiting for ownable synchronizer 0x000000076abdaa00, (a java.util.concurrent.locks.ReentrantLock$NonfairSync),
  which is held by "Thread-A"
"Thread-A":
  waiting for ownable synchronizer 0x000000076abdaa30, (a java.util.concurrent.locks.ReentrantLock$NonfairSync),
  which is held by "Thread-B"

Java stack information for the threads listed above:
===================================================
"Thread-B":
	at sun.misc.Unsafe.park(Native Method)
	- parking to wait for  <0x000000076abdaa00> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)
	at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
	at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:836)
	at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(AbstractQueuedSynchronizer.java:870)
	at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:1199)
	at java.util.concurrent.locks.ReentrantLock$NonfairSync.lock(ReentrantLock.java:209)
	at java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:285)
	at org.fool.test.DeadLockTest$2.run(DeadLockTest.java:41)
	at java.lang.Thread.run(Thread.java:745)
"Thread-A":
	at sun.misc.Unsafe.park(Native Method)
	- parking to wait for  <0x000000076abdaa30> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)
	at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
	at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:836)
	at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(AbstractQueuedSynchronizer.java:870)
	at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:1199)
	at java.util.concurrent.locks.ReentrantLock$NonfairSync.lock(ReentrantLock.java:209)
	at java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:285)
	at org.fool.test.DeadLockTest$1.run(DeadLockTest.java:20)
	at java.lang.Thread.run(Thread.java:745)

Found 1 deadlock.

Note:

tid: java线程ID 

nid: native线程ID