国土资源集约化网站群建设通知,网站内容运营是什么,微信开放平台官网登录,外链工具xg下载目录一、产生死锁的原因二、如何避免死锁一、产生死锁的原因
发生死锁的情况#xff1a; 多个线程需要同时占用多个共享资源而发生需要互相死循环等待的情况#xff0c;就是#xff0c;两个线程互相等待着对象释放锁#xff0c;一直这样僵持下去#xff0c;所以导致了死锁…
目录一、产生死锁的原因二、如何避免死锁一、产生死锁的原因
发生死锁的情况 多个线程需要同时占用多个共享资源而发生需要互相死循环等待的情况就是两个线程互相等待着对象释放锁一直这样僵持下去所以导致了死锁的产生。
产生死锁代码
package com.javaagent.thread;public class DieThread implements Runnable {public static Object obj1new Object();public static Object obj2new Object();private boolean flag;public DieThread(boolean bl){flag bl;}Overridepublic void run() {if(flag) {while(true) {synchronized(obj1) {try {Thread.sleep(1000);}catch (InterruptedException e){e.printStackTrace();}System.out.println(线程 Thread.currentThread().getName() 获取obj1锁对象等待获取obj2锁对象...);synchronized(obj2) {System.out.println(Thread.currentThread().getName() ---- obj2.);}}}}else {while(true){synchronized(obj2) {System.out.println(线程 Thread.currentThread().getName() 获取obj2锁对象等待获取obj1锁对象...);synchronized(obj1) {System.out.println(Thread.currentThread().getName() ---- obj1.);}}}}}
}public class Main {public static void main(String[] args){DieThread d1new DieThread(true);DieThread d2new DieThread(false);final Thread t1 new Thread(d1);final Thread t2 new Thread(d2);t1.setName(DieThread_1);t2.setName(DieThread_2);t1.start();t2.start();}
}输出结果
线程DieThread_2获取obj2锁对象等待获取obj1锁对象...
线程DieThread_1获取obj1锁对象等待获取obj2锁对象...采用 visualVM工具 来进行诊断结果如下图所示 从该图中我们可以看出Main的 进程ID为84114 红框1中提示 检测到死锁 然后我们点击红框3来查看 线程Dump 数据如下图 详细信息
2020-03-04 15:02:44
Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.121-b13 mixed mode):RMI TCP Connection(idle) #19 daemon prio9 os_prio31 tid0x00007ff1db108800 nid0x5f03 waiting on condition [0x0000700001961000]java.lang.Thread.State: TIMED_WAITING (parking)at sun.misc.Unsafe.park(Native Method)- parking to wait for 0x0000000796082e28 (a java.util.concurrent.SynchronousQueue$TransferStack)at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:215)at java.util.concurrent.SynchronousQueue$TransferStack.awaitFulfill(SynchronousQueue.java:460)at java.util.concurrent.SynchronousQueue$TransferStack.transfer(SynchronousQueue.java:362)at java.util.concurrent.SynchronousQueue.poll(SynchronousQueue.java:941)at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1066)at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1127)at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)at java.lang.Thread.run(Thread.java:745)Locked ownable synchronizers:- NoneJMX server connection timeout 18 #18 daemon prio9 os_prio31 tid0x00007ff1da87c800 nid0x5d03 in Object.wait() [0x000070000185e000]java.lang.Thread.State: TIMED_WAITING (on object monitor)at java.lang.Object.wait(Native Method)at com.sun.jmx.remote.internal.ServerCommunicatorAdmin$Timeout.run(ServerCommunicatorAdmin.java:168)- locked 0x00000007964a9dc8 (a [I)at java.lang.Thread.run(Thread.java:745)Locked ownable synchronizers:- NoneRMI Scheduler(0) #17 daemon prio9 os_prio31 tid0x00007ff1da895800 nid0x5b03 waiting on condition [0x000070000175b000]java.lang.Thread.State: TIMED_WAITING (parking)at sun.misc.Unsafe.park(Native Method)- parking to wait for 0x00000007960ab5d8 (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:215)at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:2078)at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1093)at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:809)at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1067)at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1127)at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)at java.lang.Thread.run(Thread.java:745)Locked ownable synchronizers:- NoneRMI TCP Connection(1)-10.0.5.39 #16 daemon prio9 os_prio31 tid0x00007ff1d99ed800 nid0x5903 runnable [0x0000700001657000]java.lang.Thread.State: RUNNABLEat java.net.SocketInputStream.socketRead0(Native Method)at java.net.SocketInputStream.socketRead(SocketInputStream.java:116)at java.net.SocketInputStream.read(SocketInputStream.java:171)at java.net.SocketInputStream.read(SocketInputStream.java:141)at java.io.BufferedInputStream.fill(BufferedInputStream.java:246)at java.io.BufferedInputStream.read(BufferedInputStream.java:265)- locked 0x00000007963eced8 (a java.io.BufferedInputStream)at java.io.FilterInputStream.read(FilterInputStream.java:83)at sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:550)at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTransport.java:826)at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.lambda$run$0(TCPTransport.java:683)at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler$$Lambda$3/657644190.run(Unknown Source)at java.security.AccessController.doPrivileged(Native Method)at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:682)at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)at java.lang.Thread.run(Thread.java:745)Locked ownable synchronizers:- 0x0000000796299c10 (a java.util.concurrent.ThreadPoolExecutor$Worker)RMI TCP Accept-0 #15 daemon prio9 os_prio31 tid0x00007ff1d9941800 nid0x570f runnable [0x0000700001555000]java.lang.Thread.State: RUNNABLEat java.net.PlainSocketImpl.socketAccept(Native Method)at java.net.AbstractPlainSocketImpl.accept(AbstractPlainSocketImpl.java:409)at java.net.ServerSocket.implAccept(ServerSocket.java:545)at java.net.ServerSocket.accept(ServerSocket.java:513)at sun.management.jmxremote.LocalRMIServerSocketFactory$1.accept(LocalRMIServerSocketFactory.java:52)at sun.rmi.transport.tcp.TCPTransport$AcceptLoop.executeAcceptLoop(TCPTransport.java:400)at sun.rmi.transport.tcp.TCPTransport$AcceptLoop.run(TCPTransport.java:372)at java.lang.Thread.run(Thread.java:745)Locked ownable synchronizers:- NoneAttach Listener #13 daemon prio9 os_prio31 tid0x00007ff1db028800 nid0x5303 waiting on condition [0x0000000000000000]java.lang.Thread.State: RUNNABLELocked ownable synchronizers:- NoneDestroyJavaVM #12 prio5 os_prio31 tid0x00007ff1da1ac000 nid0x1403 waiting on condition [0x0000000000000000]java.lang.Thread.State: RUNNABLELocked ownable synchronizers:- NoneDieThread_2 #11 prio5 os_prio31 tid0x00007ff1d9839800 nid0x5103 waiting for monitor entry [0x000070000134f000]java.lang.Thread.State: BLOCKED (on object monitor)at com.javaagent.thread.DieThread.run(DieThread.java:37)- waiting to lock 0x000000079585bee0 (a java.lang.Object)- locked 0x000000079585bef0 (a java.lang.Object)at java.lang.Thread.run(Thread.java:745)Locked ownable synchronizers:- NoneDieThread_1 #10 prio5 os_prio31 tid0x00007ff1d9835800 nid0x4f03 waiting for monitor entry [0x000070000124c000]java.lang.Thread.State: BLOCKED (on object monitor)at com.javaagent.thread.DieThread.run(DieThread.java:26)- waiting to lock 0x000000079585bef0 (a java.lang.Object)- locked 0x000000079585bee0 (a java.lang.Object)at java.lang.Thread.run(Thread.java:745)Locked ownable synchronizers:- NoneService Thread #9 daemon prio9 os_prio31 tid0x00007ff1d9835000 nid0x4b03 runnable [0x0000000000000000]java.lang.Thread.State: RUNNABLELocked ownable synchronizers:- NoneC1 CompilerThread2 #8 daemon prio9 os_prio31 tid0x00007ff1da87f800 nid0x4903 waiting on condition [0x0000000000000000]java.lang.Thread.State: RUNNABLELocked ownable synchronizers:- NoneC2 CompilerThread1 #7 daemon prio9 os_prio31 tid0x00007ff1d98c5800 nid0x4703 waiting on condition [0x0000000000000000]java.lang.Thread.State: RUNNABLELocked ownable synchronizers:- NoneC2 CompilerThread0 #6 daemon prio9 os_prio31 tid0x00007ff1da886000 nid0x4503 waiting on condition [0x0000000000000000]java.lang.Thread.State: RUNNABLELocked ownable synchronizers:- NoneMonitor Ctrl-Break #5 daemon prio5 os_prio31 tid0x00007ff1da884800 nid0x4303 runnable [0x0000700000c3a000]java.lang.Thread.State: RUNNABLEat java.net.SocketInputStream.socketRead0(Native Method)at java.net.SocketInputStream.socketRead(SocketInputStream.java:116)at java.net.SocketInputStream.read(SocketInputStream.java:171)at java.net.SocketInputStream.read(SocketInputStream.java:141)at sun.nio.cs.StreamDecoder.readBytes(StreamDecoder.java:284)at sun.nio.cs.StreamDecoder.implRead(StreamDecoder.java:326)at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:178)- locked 0x00000007958fc840 (a java.io.InputStreamReader)at java.io.InputStreamReader.read(InputStreamReader.java:184)at java.io.BufferedReader.fill(BufferedReader.java:161)at java.io.BufferedReader.readLine(BufferedReader.java:324)- locked 0x00000007958fc840 (a java.io.InputStreamReader)at java.io.BufferedReader.readLine(BufferedReader.java:389)at com.intellij.rt.execution.application.AppMainV2$1.run(AppMainV2.java:64)Locked ownable synchronizers:- NoneSignal Dispatcher #4 daemon prio9 os_prio31 tid0x00007ff1db029800 nid0x360f runnable [0x0000000000000000]java.lang.Thread.State: RUNNABLELocked ownable synchronizers:- NoneFinalizer #3 daemon prio8 os_prio31 tid0x00007ff1d9820800 nid0x3003 in Object.wait() [0x000070000092e000]java.lang.Thread.State: WAITING (on object monitor)at java.lang.Object.wait(Native Method)- waiting on 0x0000000795588ec8 (a java.lang.ref.ReferenceQueue$Lock)at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:143)- locked 0x0000000795588ec8 (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)Locked ownable synchronizers:- NoneReference Handler #2 daemon prio10 os_prio31 tid0x00007ff1d9810800 nid0x2e03 in Object.wait() [0x000070000082b000]java.lang.Thread.State: WAITING (on object monitor)at java.lang.Object.wait(Native Method)- waiting on 0x0000000795586b68 (a java.lang.ref.Reference$Lock)at java.lang.Object.wait(Object.java:502)at java.lang.ref.Reference.tryHandlePending(Reference.java:191)- locked 0x0000000795586b68 (a java.lang.ref.Reference$Lock)at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:153)Locked ownable synchronizers:- NoneVM Thread os_prio31 tid0x00007ff1da026800 nid0x2c03 runnable GC task thread#0 (ParallelGC) os_prio31 tid0x00007ff1d9810000 nid0x2403 runnable GC task thread#1 (ParallelGC) os_prio31 tid0x00007ff1da00d000 nid0x2603 runnable GC task thread#2 (ParallelGC) os_prio31 tid0x00007ff1da00d800 nid0x2803 runnable GC task thread#3 (ParallelGC) os_prio31 tid0x00007ff1da00e000 nid0x2a03 runnable VM Periodic Task Thread os_prio31 tid0x00007ff1da80d000 nid0x4d03 waiting on condition JNI global references: 354Found one Java-level deadlock:DieThread_2:waiting to lock monitor 0x00007ff1da80ad58 (object 0x000000079585bee0, a java.lang.Object),which is held by DieThread_1
DieThread_1:waiting to lock monitor 0x00007ff1da808418 (object 0x000000079585bef0, a java.lang.Object),which is held by DieThread_2Java stack information for the threads listed above:DieThread_2:at com.javaagent.thread.DieThread.run(DieThread.java:37)- waiting to lock 0x000000079585bee0 (a java.lang.Object)- locked 0x000000079585bef0 (a java.lang.Object)at java.lang.Thread.run(Thread.java:745)
DieThread_1:at com.javaagent.thread.DieThread.run(DieThread.java:26)- waiting to lock 0x000000079585bef0 (a java.lang.Object)- locked 0x000000079585bee0 (a java.lang.Object)at java.lang.Thread.run(Thread.java:745)Found 1 deadlock.通过上面的线程Dump文件信息我们可以看出来发生了死锁下面也列出了java级别的锁问题和栈信息
Found one Java-level deadlock:DieThread_2:waiting to lock monitor 0x00007ff1da80ad58 (object 0x000000079585bee0, a java.lang.Object),which is held by DieThread_1
DieThread_1:waiting to lock monitor 0x00007ff1da808418 (object 0x000000079585bef0, a java.lang.Object),which is held by DieThread_2Java stack information for the threads listed above:DieThread_2:at com.javaagent.thread.DieThread.run(DieThread.java:37)- waiting to lock 0x000000079585bee0 (a java.lang.Object)- locked 0x000000079585bef0 (a java.lang.Object)at java.lang.Thread.run(Thread.java:745)
DieThread_1:at com.javaagent.thread.DieThread.run(DieThread.java:26)- waiting to lock 0x000000079585bef0 (a java.lang.Object)- locked 0x000000079585bee0 (a java.lang.Object)at java.lang.Thread.run(Thread.java:745)Found 1 deadlock.并且栈信息中可以定位到死锁发生的地方。
如果解决死锁那是因为代码的逻辑存在问题可以调整代码的逻辑或者业务来避免死锁。
二、如何避免死锁 避免一个线程同时获取多个锁 避免一个线程在锁内同时占用多个资源尽量保证每个锁只占用一个资源 尝试使用定时锁使用 lock.tryLock(timeout) 来替代使用内部锁机制。 对于数据库锁加锁和解锁必须在一个数据库连接里否则会出现解锁失败的情况。
