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建筑人才网官网首页,青岛seo公司,重庆网站建设seo优化,网站设计流程的步骤包括死锁是两个或者两个以上的线程在执行过程中,因争夺资源而造成的一种互斥等待现象,若没有外界干涉那么它们将无法推进下去。如果系统资源不足,进程的资源请求都得到满足,死锁出现的可能性就很低,否则就会因为争夺有限的…

死锁是两个或者两个以上的线程在执行过程中,因争夺资源而造成的一种互斥等待现象,若没有外界干涉那么它们将无法推进下去。如果系统资源不足,进程的资源请求都得到满足,死锁出现的可能性就很低,否则就会因为争夺有限的资源而陷入死锁。

死锁案例

 public static void main(String[] args) {final Object a = new Object();final Object b = new Object();new Thread(() -> {synchronized (a) {try {System.out.println(Thread.currentThread().getName() + ",持有a锁希望获得b锁");TimeUnit.SECONDS.sleep(2);} catch (InterruptedException e) {e.printStackTrace();}synchronized (b) {System.out.println(Thread.currentThread() + ",成功获得b锁");}}}, "t1").start();new Thread(() -> {synchronized (b) {try {System.out.println(Thread.currentThread().getName() + ",持有b锁希望获得a锁");TimeUnit.SECONDS.sleep(2);} catch (InterruptedException e) {e.printStackTrace();}synchronized (a) {System.out.println(Thread.currentThread() + ",成功获得a锁");}}}, "t2").start();}

        打印结果:

t1,持有a锁希望获得b锁
t2,持有b锁希望获得a锁

        可以看到案例中,t1持有a锁,希望获得b锁。而t2持有b锁,希望获得a锁。t1和t2就僵持在这里,程序得不到终止。

排除死锁

        通过jdk自带的工具、命令我们可以查看当前进程,以及进程中是否存在死锁情况。

jps -l

        通过jps -l 我们可以看到当前系统中正在运行的java进程:

$ jps -l
18064 com.tlh.comf._死锁及排查
3568
10644 org.jetbrains.jps.cmdline.Launcher
16676 sun.tools.jps.Jps
19544 org.jetbrains.idea.maven.server.RemoteMavenServer

        我们看到我们的死锁案例的进程id为:18064

jstack #{进程id}

        通过jstack #{进程id},我们可以查看当前进程中线程的情况和否存在死锁。比如,我们的死锁案例进程id为:18064。我们通过jstack 18064查看到的信息:

$ jstack 18064
2023-07-28 23:57:25
Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.91-b15 mixed mode):"DestroyJavaVM" #14 prio=5 os_prio=0 tid=0x0000000002ff3800 nid=0x50cc waiting on condition [0x0000000000000000]java.lang.Thread.State: RUNNABLE"t2" #13 prio=5 os_prio=0 tid=0x000000002980d800 nid=0x4c94 waiting for monitor entry [0x000000002a05e000]java.lang.Thread.State: BLOCKED (on object monitor)at com.tlh.comf._死锁及排查.lambda$main$1(_死锁及排查.java:42)- waiting to lock <0x00000007161d8520> (a java.lang.Object)- locked <0x00000007161d8530> (a java.lang.Object)at com.tlh.comf._死锁及排查$$Lambda$2/824909230.run(Unknown Source)at java.lang.Thread.run(Thread.java:745)"t1" #12 prio=5 os_prio=0 tid=0x000000002980b000 nid=0x4a84 waiting for monitor entry [0x0000000029f5f000]java.lang.Thread.State: BLOCKED (on object monitor)at com.tlh.comf._死???及排查.lambda$main$0(_死锁及排查.java:28)- waiting to lock <0x00000007161d8530> (a java.lang.Object)- locked <0x00000007161d8520> (a java.lang.Object)at com.tlh.comf._死锁及排查$$Lambda$1/1534030866.run(Unknown Source)at java.lang.Thread.run(Thread.java:745)"Service Thread" #11 daemon prio=9 os_prio=0 tid=0x0000000027c77000 nid=0x50a4 runnable [0x0000000000000000]java.lang.Thread.State: RUNNABLE"C1 CompilerThread3" #10 daemon prio=9 os_prio=2 tid=0x0000000027b8a800 nid=0x1dc8 waiting on condition [0x0000000000000000]java.lang.Thread.State: RUNNABLE"C2 CompilerThread2" #9 daemon prio=9 os_prio=2 tid=0x0000000027b84000 nid=0x2d4 waiting on condition [0x0000000000000000]java.lang.Thread.State: RUNNABLE"C2 CompilerThread1" #8 daemon prio=9 os_prio=2 tid=0x0000000027b81000 nid=0xa8 waiting on condition [0x0000000000000000]java.lang.Thread.State: RUNNABLE"C2 CompilerThread0" #7 daemon prio=9 os_prio=2 tid=0x0000000027b7e800 nid=0x39d8 waiting on condition [0x0000000000000000]java.lang.Thread.State: RUNNABLE"Monitor Ctrl-Break" #6 daemon prio=5 os_prio=0 tid=0x0000000027b64000 nid=0x48fc runnable [0x000000002905e000]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:170)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 <0x00000007162cf3f0> (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 <0x00000007162cf3f0> (a java.io.InputStreamReader)at java.io.BufferedReader.readLine(BufferedReader.java:389)at com.intellij.rt.execution.application.AppMainV2$1.run(AppMainV2.java:64)"Attach Listener" #5 daemon prio=5 os_prio=2 tid=0x0000000027a11800 nid=0x5384 waiting on condition [0x0000000000000000]java.lang.Thread.State: RUNNABLE"Signal Dispatcher" #4 daemon prio=9 os_prio=2 tid=0x00000000279be000 nid=0x4fc8 runnable [0x0000000000000000]java.lang.Thread.State: RUNNABLE"Finalizer" #3 daemon prio=8 os_prio=1 tid=0x00000000262d3800 nid=0x1204 in Object.wait() [0x0000000028cfe000]java.lang.Thread.State: WAITING (on object monitor)at java.lang.Object.wait(Native Method)- waiting on <0x0000000716008ee0> (a java.lang.ref.ReferenceQueue$Lock)at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:143)- locked <0x0000000716008ee0> (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=2 tid=0x00000000262cc800 nid=0x4de4 in Object.wait() [0x0000000028bff000]java.lang.Thread.State: WAITING (on object monitor)at java.lang.Object.wait(Native Method)- waiting on <0x0000000716006b50> (a java.lang.ref.Reference$Lock)at java.lang.Object.wait(Object.java:502)at java.lang.ref.Reference.tryHandlePending(Reference.java:191)- locked <0x0000000716006b50> (a java.lang.ref.Reference$Lock)at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:153)"VM Thread" os_prio=2 tid=0x0000000027982800 nid=0x5298 runnable"GC task thread#0 (ParallelGC)" os_prio=0 tid=0x0000000003009000 nid=0x4cbc runnable"GC task thread#1 (ParallelGC)" os_prio=0 tid=0x000000000300a800 nid=0x3a54 runnable"GC task thread#2 (ParallelGC)" os_prio=0 tid=0x000000000300c000 nid=0x4098 runnable"GC task thread#3 (ParallelGC)" os_prio=0 tid=0x000000000300d800 nid=0x2e78 runnable"GC task thread#4 (ParallelGC)" os_prio=0 tid=0x000000000300f800 nid=0x3f98 runnable"GC task thread#5 (ParallelGC)" os_prio=0 tid=0x0000000003012000 nid=0xd60 runnable"GC task thread#6 (ParallelGC)" os_prio=0 tid=0x0000000003015000 nid=0x3414 runnable"GC task thread#7 (ParallelGC)" os_prio=0 tid=0x0000000003016000 nid=0x2204 runnable"GC task thread#8 (ParallelGC)" os_prio=0 tid=0x0000000003017800 nid=0x4fbc runnable"GC task thread#9 (ParallelGC)" os_prio=0 tid=0x0000000003018800 nid=0x49e8 runnable"VM Periodic Task Thread" os_prio=2 tid=0x0000000027ced000 nid=0x4f44 waiting on conditionJNI global references: 335Found one Java-level deadlock:
=============================
"t2":waiting to lock monitor 0x00000000262d0678 (object 0x00000007161d8520, a java.lang.Object),which is held by "t1"
"t1":waiting to lock monitor 0x00000000262d2e58 (object 0x00000007161d8530, a java.lang.Object),which is held by "t2"Java stack information for the threads listed above:
===================================================
"t2":at com.tlh.comf._死锁及排查.lambda$main$1(_死锁及排查.java:42)- waiting to lock <0x00000007161d8520> (a java.lang.Object)- locked <0x00000007161d8530> (a java.lang.Object)at com.tlh.comf._死锁及排查$$Lambda$2/824909230.run(Unknown Source)at java.lang.Thread.run(Thread.java:745)
"t1":at com.tlh.comf._死锁及排查.lambda$main$0(_死锁及排查.java:28)- waiting to lock <0x00000007161d8530> (a java.lang.Object)- locked <0x00000007161d8520> (a java.lang.Object)at com.tlh.comf._死锁及排查$$Lambda$1/1534030866.run(Unknown Source)at java.lang.Thread.run(Thread.java:745)Found 1 deadlock.

        打印的信息中,最上部分我们可以看到t1和t2的状态均为:BLOCKED(阻塞)状态。打印信息的最下部分,我们可以看到:Found one Java-level deadlock,提示信息说,t2在等待 lock monitor 0x00000000262d0678,但是被t1持有。t1在等待lock monitor 0x00000000262d2e58,但是被t2持有。

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