1、死锁例子

代码例子

  1. public class Main {
  2.     public static String obj1 = "obj1";
  3.     public static String obj2 = "obj2";
  4.     public static void main(String[] args) {
  5.         LockA la = new LockA();
  6.         Thread threadA = new Thread(la);
  7.         threadA.start();
  9.         LockB lb = new LockB();
  10.         Thread threadB = new Thread(lb);
  11.         threadB.start();
  13.         try {
  14.             Thread.sleep(5000);
  15.         } catch (InterruptedException e) {
  16.             e.printStackTrace();
  17.         }
  19.         // 此时两个线程都出BLOCKED状态
  20.         // BLOCKED
  21.         System.out.println(threadA.getState());
  22.         // BLOCKED
  23.         System.out.println(threadB.getState());
  24.     }
  25. }
  26. class LockA implements Runnable{
  27.     public void run() {
  28.         try {
  29.             System.out.println(System.currentTimeMillis() + " LockA 开始执行");
  30.             while(true){
  31.                 synchronized (Main.obj1) {
  32.                     System.out.println(System.currentTimeMillis() + " LockA 锁住 obj1");
  33.                     Thread.sleep(3000); // 此处等待是给B能锁住机会
  34.                     synchronized (Main.obj2) {
  35.                         System.out.println(System.currentTimeMillis() + " LockA 锁住 obj2");
  36.                         Thread.sleep(60 * 1000); // 为测试，占用了就不放
  37.                     }
  38.                 }
  39.             }
  40.         } catch (Exception e) {
  41.             e.printStackTrace();
  42.         }
  43.     }
  44. }
  45. class LockB implements Runnable{
  46.     public void run() {
  47.         try {
  48.             System.out.println(System.currentTimeMillis() + " LockB 开始执行");
  49.             while(true){
  50.                 System.out.println(System.currentTimeMillis() + " LockB 锁住 obj2");
  51.                 synchronized (Main.obj2) {
  52.                     System.out.println(System.currentTimeMillis() + " LockB 锁住 obj2");
  53.                     Thread.sleep(3000); // 此处等待是给A能锁住机会
  54.                     synchronized (Main.obj1) {
  55.                         System.out.println(System.currentTimeMillis() + " LockB 锁住 obj1");
  56.                         Thread.sleep(60 * 1000); // 为测试，占用了就不放
  57.                     }
  58.                 }
  59.             }
  60.         } catch (Exception e) {
  61.             e.printStackTrace();
  62.         }
  63.     }
  64. }

堆栈排查死锁

  • IDEA左边有个相机的图标，可以打印堆栈信息

image.png

  • 日志分析结果，deadlock死锁关键字
    • Thread-1：持有一个String锁d0，等待获取另一个String锁a0
    • Thread-0：持有一个String锁a0，等待获取另一个String锁d0
    • 两个线程持有一个锁，再去尝试获取对方持有的锁

      Found one Java-level deadlock:

      “Thread-1”:

waiting to lock monitor 0x00000206d33fef48 (object 0x000000076b4100a0, a java.lang.String),

which is held by “Thread-0”

“Thread-0”:

waiting to lock monitor 0x00000206d33fede8 (object 0x000000076b4100d0, a java.lang.String),

which is held by “Thread-1”

Java stack information for the threads listed above:

===================================================

“Thread-1”:

  1. at com.wangchun.LockB.run(Main.java:56)
  3. - waiting to lock <0x000000076b4100a0> (a java.lang.String)
  5. - locked <0x000000076b4100d0> (a java.lang.String)
  7. at java.lang.Thread.run(Thread.java:748)

“Thread-0”:

  1. at com.wangchun.LockA.run(Main.java:37)
  3. - waiting to lock <0x000000076b4100d0> (a java.lang.String)
  5. - locked <0x000000076b4100a0> (a java.lang.String)
  7. at java.lang.Thread.run(Thread.java:748)

Found 1 deadlock.

  1. 2021-08-24 00:13:38
  2. Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.271-b09 mixed mode):
  4. "DestroyJavaVM" #14 prio=5 os_prio=0 tid=0x00000206b86c7000 nid=0x1b68 waiting on condition [0x0000000000000000]
  5.    java.lang.Thread.State: RUNNABLE
  7. "Thread-1" #13 prio=5 os_prio=0 tid=0x00000206d5948000 nid=0x16d8 waiting for monitor entry [0x000000dc6bdfe000]
  8.    java.lang.Thread.State: BLOCKED (on object monitor)
  9.     at com.wangchun.LockB.run(Main.java:56)
  10.     - waiting to lock <0x000000076b4100a0> (a java.lang.String)
  11.     - locked <0x000000076b4100d0> (a java.lang.String)
  12.     at java.lang.Thread.run(Thread.java:748)
  14. "Thread-0" #12 prio=5 os_prio=0 tid=0x00000206d5940000 nid=0x33f4 waiting for monitor entry [0x000000dc6bcfe000]
  15.    java.lang.Thread.State: BLOCKED (on object monitor)
  16.     at com.wangchun.LockA.run(Main.java:37)
  17.     - waiting to lock <0x000000076b4100d0> (a java.lang.String)
  18.     - locked <0x000000076b4100a0> (a java.lang.String)
  19.     at java.lang.Thread.run(Thread.java:748)
  21. "Service Thread" #11 daemon prio=9 os_prio=0 tid=0x00000206d5939800 nid=0x3e04 runnable [0x0000000000000000]
  22.    java.lang.Thread.State: RUNNABLE
  24. "C1 CompilerThread3" #10 daemon prio=9 os_prio=2 tid=0x00000206d586e800 nid=0x3364 waiting on condition [0x0000000000000000]
  25.    java.lang.Thread.State: RUNNABLE
  27. "C2 CompilerThread2" #9 daemon prio=9 os_prio=2 tid=0x00000206d586a800 nid=0x3b4 waiting on condition [0x0000000000000000]
  28.    java.lang.Thread.State: RUNNABLE
  30. "C2 CompilerThread1" #8 daemon prio=9 os_prio=2 tid=0x00000206d586a000 nid=0x270 waiting on condition [0x0000000000000000]
  31.    java.lang.Thread.State: RUNNABLE
  33. "C2 CompilerThread0" #7 daemon prio=9 os_prio=2 tid=0x00000206d5867000 nid=0x1d10 waiting on condition [0x0000000000000000]
  34.    java.lang.Thread.State: RUNNABLE
  36. "Monitor Ctrl-Break" #6 daemon prio=5 os_prio=0 tid=0x00000206d5864800 nid=0x2e80 runnable [0x000000dc6b5fe000]
  37.    java.lang.Thread.State: RUNNABLE
  38.     at java.net.SocketInputStream.socketRead0(Native Method)
  39.     at java.net.SocketInputStream.socketRead(SocketInputStream.java:116)
  40.     at java.net.SocketInputStream.read(SocketInputStream.java:171)
  41.     at java.net.SocketInputStream.read(SocketInputStream.java:141)
  42.     at sun.nio.cs.StreamDecoder.readBytes(StreamDecoder.java:284)
  43.     at sun.nio.cs.StreamDecoder.implRead(StreamDecoder.java:326)
  44.     at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:178)
  45.     - locked <0x000000076b3120a8> (a java.io.InputStreamReader)
  46.     at java.io.InputStreamReader.read(InputStreamReader.java:184)
  47.     at java.io.BufferedReader.fill(BufferedReader.java:161)
  48.     at java.io.BufferedReader.readLine(BufferedReader.java:324)
  49.     - locked <0x000000076b3120a8> (a java.io.InputStreamReader)
  50.     at java.io.BufferedReader.readLine(BufferedReader.java:389)
  51.     at com.intellij.rt.execution.application.AppMainV2$1.run(AppMainV2.java:49)
  53. "Attach Listener" #5 daemon prio=5 os_prio=2 tid=0x00000206d3432800 nid=0x1118 runnable [0x0000000000000000]
  54.    java.lang.Thread.State: RUNNABLE
  56. "Signal Dispatcher" #4 daemon prio=9 os_prio=2 tid=0x00000206d342f800 nid=0x3c18 waiting on condition [0x0000000000000000]
  57.    java.lang.Thread.State: RUNNABLE
  59. "Finalizer" #3 daemon prio=8 os_prio=1 tid=0x00000206d33ff800 nid=0x3cfc in Object.wait() [0x000000dc6b2fe000]
  60.    java.lang.Thread.State: WAITING (on object monitor)
  61.     at java.lang.Object.wait(Native Method)
  62.     - waiting on <0x000000076b188ee0> (a java.lang.ref.ReferenceQueue$Lock)
  63.     at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:144)
  64.     - locked <0x000000076b188ee0> (a java.lang.ref.ReferenceQueue$Lock)
  65.     at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:165)
  66.     at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:216)
  68. "Reference Handler" #2 daemon prio=10 os_prio=2 tid=0x00000206d33f8800 nid=0x5dc in Object.wait() [0x000000dc6b1ff000]
  69.    java.lang.Thread.State: WAITING (on object monitor)
  70.     at java.lang.Object.wait(Native Method)
  71.     - waiting on <0x000000076b186c00> (a java.lang.ref.Reference$Lock)
  72.     at java.lang.Object.wait(Object.java:502)
  73.     at java.lang.ref.Reference.tryHandlePending(Reference.java:191)
  74.     - locked <0x000000076b186c00> (a java.lang.ref.Reference$Lock)
  75.     at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:153)
  77. "VM Thread" os_prio=2 tid=0x00000206d33cf000 nid=0x2214 runnable 
  79. "GC task thread#0 (ParallelGC)" os_prio=0 tid=0x00000206b86e1000 nid=0x2850 runnable 
  81. "GC task thread#1 (ParallelGC)" os_prio=0 tid=0x00000206b86e2000 nid=0x1614 runnable 
  83. "GC task thread#2 (ParallelGC)" os_prio=0 tid=0x00000206b86e3800 nid=0x2178 runnable 
  85. "GC task thread#3 (ParallelGC)" os_prio=0 tid=0x00000206b86e5800 nid=0x308c runnable 
  87. "GC task thread#4 (ParallelGC)" os_prio=0 tid=0x00000206b86e6800 nid=0x375c runnable 
  89. "GC task thread#5 (ParallelGC)" os_prio=0 tid=0x00000206b86e7800 nid=0x1fe8 runnable 
  91. "GC task thread#6 (ParallelGC)" os_prio=0 tid=0x00000206b86ea800 nid=0x3f74 runnable 
  93. "GC task thread#7 (ParallelGC)" os_prio=0 tid=0x00000206b86eb800 nid=0x288c runnable 
  95. "GC task thread#8 (ParallelGC)" os_prio=0 tid=0x00000206b86ec800 nid=0x2350 runnable 
  97. "GC task thread#9 (ParallelGC)" os_prio=0 tid=0x00000206b86ed800 nid=0x1fb0 runnable 
  99. "VM Periodic Task Thread" os_prio=2 tid=0x00000206d593e000 nid=0x3a34 waiting on condition 
  101. JNI global references: 12
  104. Found one Java-level deadlock:
  105. =============================
  106. "Thread-1":
  107.   waiting to lock monitor 0x00000206d33fef48 (object 0x000000076b4100a0, a java.lang.String),
  108.   which is held by "Thread-0"
  109. "Thread-0":
  110.   waiting to lock monitor 0x00000206d33fede8 (object 0x000000076b4100d0, a java.lang.String),
  111.   which is held by "Thread-1"
  113. Java stack information for the threads listed above:
  114. ===================================================
  115. "Thread-1":
  116.     at com.wangchun.LockB.run(Main.java:56)
  117.     - waiting to lock <0x000000076b4100a0> (a java.lang.String)
  118.     - locked <0x000000076b4100d0> (a java.lang.String)
  119.     at java.lang.Thread.run(Thread.java:748)
  120. "Thread-0":
  121.     at com.wangchun.LockA.run(Main.java:37)
  122.     - waiting to lock <0x000000076b4100d0> (a java.lang.String)
  123.     - locked <0x000000076b4100a0> (a java.lang.String)
  124.     at java.lang.Thread.run(Thread.java:748)
  126. Found 1 deadlock.
  128. Heap
  129.  PSYoungGen      total 76288K, used 10486K [0x000000076b180000, 0x0000000770680000, 0x00000007c0000000)
  130.   eden space 65536K, 16% used [0x000000076b180000,0x000000076bbbd950,0x000000076f180000)
  131.   from space 10752K, 0% used [0x000000076fc00000,0x000000076fc00000,0x0000000770680000)
  132.   to   space 10752K, 0% used [0x000000076f180000,0x000000076f180000,0x000000076fc00000)
  133.  ParOldGen       total 175104K, used 0K [0x00000006c1400000, 0x00000006cbf00000, 0x000000076b180000)
  134.   object space 175104K, 0% used [0x00000006c1400000,0x00000006c1400000,0x00000006cbf00000)
  135.  Metaspace       used 3306K, capacity 4564K, committed 4864K, reserved 1056768K
  136.   class space    used 361K, capacity 388K, committed 512K, reserved 1048576K