java-level deadlock
如下代碼可以模擬java死鎖，注意：當出現死鎖時，應用程式是無回應的，錯誤資訊：
Found one Java-level deadlock:
=============================
"Thread-1":
waiting to lock monitor 0x000000001c773158 (object 0x000000076bbc06b8, a java.util.concurrent.Concurren
tHashMap),
which is held by "Thread-0"
"Thread-0":
waiting to lock monitor 0x000000001c774548 (object 0x000000076bbc06f8, a java.lang.Object),
which is held by "Thread-1"
deadlock demo及deadlock資訊
上代碼：
import java.util.concurrent.ConcurrentHashMap; import static java.util.concurrent.TimeUnit.SECONDS; public class TestDeadlockMain { private static final ConcurrentHashMap<String, String> concurrentHashMap1 = new ConcurrentHashMap<>(128); private static final Object concurrentHashMap2 = new Object(); public static void main(String[] args) { new Thread(() -> { synchronized (concurrentHashMap1) { // 模擬邏輯執行 try { SECONDS.sleep(1L); } catch (InterruptedException e) { e.printStackTrace(); } synchronized (concurrentHashMap2) { // 模擬邏輯執行 System.out.println("test deadlock"); } } }).start(); new Thread(() -> { synchronized (concurrentHashMap2) { synchronized (concurrentHashMap1) { // 模擬邏輯執行 try { SECONDS.sleep(1L); } catch (InterruptedException e) { e.printStackTrace(); } } } }).start(); new Thread(()->{ while (true){ System.out.println(System.currentTimeMillis()); try { SECONDS.sleep(1); } catch (InterruptedException e) { e.printStackTrace(); } } }).start(); } }
運行程式，通過控制臺日志是無法看到死鎖資訊的，只能看到第三個執行緒在間隔1s不停的打日志，卻無法看到另外兩個執行緒在干啥，
如果是所呼叫的程式有用戶界面的話，就會看到長時間無回應或超時的現象，
至于這個demo呢，我們可以借助IDEA的Terminal視窗，執行jps -l 命令，找到當前執行的java程式的行程pid， 接下來執行 jstack pid 命令，查看JVM里的執行緒快照資訊，
如下貼出來Terminal視窗的內容：
D:\SourceProject\account\target\test-classes\com\emaxcard\jvm>jps -l 24912 21556 org.jetbrains.jps.cmdline.Launcher 28840 com.emaxcard.jvm.TestDeadlockMain 30328 sun.tools.jps.Jps 13644 org.jetbrains.idea.maven.server.RemoteMavenServer D:\SourceProject\account\target\test-classes\com\emaxcard\jvm>jstack 28840 2022-08-24 20:56:11 Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.40-b25 mixed mode): "DestroyJavaVM" #14 prio=5 os_prio=0 tid=0x0000000002a58800 nid=0x6bf4 waiting on condition [0x0000000000 000000] java.lang.Thread.State: RUNNABLE "Thread-1" #13 prio=5 os_prio=0 tid=0x000000001fdba800 nid=0x4f88 waiting for monitor entry [0x0000000020 e1f000] java.lang.Thread.State: BLOCKED (on object monitor) at com.emaxcard.jvm.TestDeadlockMain.lambda$main$1(TestDeadlockMain.java:41) - waiting to lock <0x000000076bbc06b8> (a java.util.concurrent.ConcurrentHashMap) - locked <0x000000076bbc06f8> (a java.lang.Object) at com.emaxcard.jvm.TestDeadlockMain$$Lambda$2/654845766.run(Unknown Source) at java.lang.Thread.run(Thread.java:745) "Thread-0" #12 prio=5 os_prio=0 tid=0x000000001fcf8000 nid=0x6ecc waiting for monitor entry [0x0000000020 d1e000] java.lang.Thread.State: BLOCKED (on object monitor) at com.emaxcard.jvm.TestDeadlockMain.lambda$main$0(TestDeadlockMain.java:33) - waiting to lock <0x000000076bbc06f8> (a java.lang.Object) - locked <0x000000076bbc06b8> (a java.util.concurrent.ConcurrentHashMap) at com.emaxcard.jvm.TestDeadlockMain$$Lambda$1/2101842856.run(Unknown Source) at java.lang.Thread.run(Thread.java:745) "Service Thread" #11 daemon prio=9 os_prio=0 tid=0x000000001f53d800 nid=0x72d0 runnable [0x00000000000000 00] java.lang.Thread.State: RUNNABLE "C1 CompilerThread3" #10 daemon prio=9 os_prio=2 tid=0x000000001f4ea800 nid=0x948 waiting on condition [0 x0000000000000000] java.lang.Thread.State: RUNNABLE "C2 CompilerThread2" #9 daemon prio=9 os_prio=2 tid=0x000000001f4e8000 nid=0x5ed0 waiting on condition [0 x0000000000000000] java.lang.Thread.State: RUNNABLE "C2 CompilerThread1" #8 daemon prio=9 os_prio=2 tid=0x000000001f4e3000 nid=0x6130 waiting on condition [0 x0000000000000000] java.lang.Thread.State: RUNNABLE "C2 CompilerThread0" #7 daemon prio=9 os_prio=2 tid=0x000000001f4e0800 nid=0x6804 waiting on condition [0 x0000000000000000] java.lang.Thread.State: RUNNABLE "Monitor Ctrl-Break" #6 daemon prio=5 os_prio=0 tid=0x000000001f4a8000 nid=0x52bc runnable [0x000000001f6 4e000] java.lang.Thread.State: RUNNABLE at 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 <0x000000076bce5ac8> (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 <0x000000076bce5ac8> (a java.io.InputStreamReader) at java.io.BufferedReader.readLine(BufferedReader.java:389) at com.intellij.rt.execution.application.AppMainV2$1.run(AppMainV2.java:61) "Attach Listener" #5 daemon prio=5 os_prio=2 tid=0x000000001e7d2000 nid=0x6478 waiting on condition [0x00 00000000000000] java.lang.Thread.State: RUNNABLE "Signal Dispatcher" #4 daemon prio=9 os_prio=2 tid=0x000000001e7d1800 nid=0x5e4c runnable [0x000000000000 0000] java.lang.Thread.State: RUNNABLE "Finalizer" #3 daemon prio=8 os_prio=1 tid=0x000000001c774800 nid=0x5df0 in Object.wait() [0x000000001e73 e000] java.lang.Thread.State: WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x000000076b306f58> (a java.lang.ref.ReferenceQueue$Lock) at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:143) - locked <0x000000076b306f58> (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=0x000000001c76e000 nid=0x6828 in Object.wait() [0x000 000001e63f000] java.lang.Thread.State: WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x000000076b306998> (a java.lang.ref.Reference$Lock) at java.lang.Object.wait(Object.java:502) at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:157) - locked <0x000000076b306998> (a java.lang.ref.Reference$Lock) "VM Thread" os_prio=2 tid=0x000000001c76a000 nid=0x3384 runnable "GC task thread#0 (ParallelGC)" os_prio=0 tid=0x0000000002a72000 nid=0x6d44 runnable "GC task thread#1 (ParallelGC)" os_prio=0 tid=0x0000000002a73800 nid=0x61c8 runnable "GC task thread#2 (ParallelGC)" os_prio=0 tid=0x0000000002a75000 nid=0x6a00 runnable "GC task thread#3 (ParallelGC)" os_prio=0 tid=0x0000000002a77800 nid=0x5e6c runnable "GC task thread#4 (ParallelGC)" os_prio=0 tid=0x0000000002a7a000 nid=0x480c runnable "GC task thread#5 (ParallelGC)" os_prio=0 tid=0x0000000002a7b000 nid=0x497c runnable "GC task thread#6 (ParallelGC)" os_prio=0 tid=0x0000000002a7e000 nid=0x13f8 runnable "GC task thread#7 (ParallelGC)" os_prio=0 tid=0x0000000002a7f800 nid=0x40b4 runnable "VM Periodic Task Thread" os_prio=2 tid=0x000000001f53e800 nid=0x7314 waiting on condition JNI global references: 330 Found one Java-level deadlock: ============================= "Thread-1": waiting to lock monitor 0x000000001c773158 (object 0x000000076bbc06b8, a java.util.concurrent.Concurren tHashMap), which is held by "Thread-0" "Thread-0": waiting to lock monitor 0x000000001c774548 (object 0x000000076bbc06f8, a java.lang.Object), which is held by "Thread-1" Java stack information for the threads listed above: =================================================== "Thread-1": at com.emaxcard.jvm.TestDeadlockMain.lambda$main$1(TestDeadlockMain.java:41) - waiting to lock <0x000000076bbc06b8> (a java.util.concurrent.ConcurrentHashMap) - locked <0x000000076bbc06f8> (a java.lang.Object) at com.emaxcard.jvm.TestDeadlockMain$$Lambda$2/654845766.run(Unknown Source) at java.lang.Thread.run(Thread.java:745) "Thread-0": at com.emaxcard.jvm.TestDeadlockMain.lambda$main$0(TestDeadlockMain.java:33) - waiting to lock <0x000000076bbc06f8> (a java.lang.Object) - locked <0x000000076bbc06b8> (a java.util.concurrent.ConcurrentHashMap) at com.emaxcard.jvm.TestDeadlockMain$$Lambda$1/2101842856.run(Unknown Source) at java.lang.Thread.run(Thread.java:745) Found 1 deadlock.
jstack簡介
- jstack命令用于列印指定Java行程、核心檔案或遠程除錯服務器的Java執行緒的Java堆疊跟蹤資訊[1]，
- jstack命令可以生成JVM當前時刻的執行緒快照，執行緒快照是當前JVM內每一條執行緒正在執行的方法堆疊的集合，生成執行緒快照的主要目的是定位執行緒出現長時間停頓的原因，如執行緒間死鎖、死回圈、請求外部資源導致的長時間等待等，
- 如果java程式崩潰生成core檔案，jstack工具可以用來獲得core檔案的java stack和native stack的資訊，從而可以輕松地知道java程式是如何崩潰和在程式何處發生問題，
- 當指定的行程在64位Java虛擬機上運行時，可能需要指定-J-d64選項，例如:jstack -J-d64 -m pid，
- 該命令可能在未來的版本中不可用！！！
語法
jstack [ options ] pid
當看到一些不好的代碼時，會發現我還算優秀；當看到優秀的代碼時，也才意識到持續學習的重要！--buguge
本文來自博客園，轉載請注明原文鏈接：https://www.cnblogs.com/buguge/p/16622318.html
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