JVM监控及诊断工具-命令之jcmd
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1、简介
在JDK1.7以后，新增了一个命令行工具jcmd它是一个多功能的工具，可以用来实现前面除jsat之外所有命令的功能。比如：用它来导出堆、内存使用、查看]ava进程、导出线程信
息、执行GC、JVM运行时间等。jcmd拥有jmap的大部分功能，并且在Oracle的官方网站上也推荐使
用jcmd命令代jmap命令
2、命令：jcmd -l
可以查看当前正在运行的所有JVM进程，和jps有点类似
3、命令：jcmd pid PerfCounter.print
这样我们就能看到12735这个进程的性能计数器。
4、jcmd <pid> help
获得指定进程可用的命令列表
例如：
C:\\Users\\86136>jps 10192 Jps 3136 Launcher 14628 JstackSyncTest 7000 9592 RemoteMavenServer C:\\Users\\86136>jcmd 14628 help 14628: The following commands are available: JFR.stop JFR.start JFR.dump JFR.check VM.native_memory VM.check_commercial_features VM.unlock_commercial_features ManagementAgent.stop ManagementAgent.start_local ManagementAgent.start GC.rotate_log Thread.print GC.class_stats GC.class_histogram GC.heap_dump GC.run_finalization GC.run VM.uptime VM.flags VM.system_properties VM.command_line VM.version help For more information about a specific command use 'help <command>'. C:\\Users\\86136>由上可以发现所有可以执行的命令
5、jcmd pid GC.heap_dump -all 文件路径
- 作用：生成Java堆Dump文件（HPROF格式）
- 影响：高（取决于Java堆大小和内容。除非指定了-all选项，否则会导致Full GC
- 所需权限：java.lang.management.ManagementPermission(monitor)
- options：选项，必须使用key或者key=value的语法指定，可用的options如下：
- -all：（可选）转储所有对象，包括不可达对象（BOOLEAN，false）
- arguments：参数，可用的参数如下：
- filename：Dump文件的名称（STRING，无默认值）
示例：
windows生成的文件会自动保存到pid进程项目的目录下：
6、jcmd pid Thread.print -l
- 作用：打印所有带有堆栈跟踪的线程
- 影响：中（取决于线程数）
- 所需权限：java.lang.management.ManagementPermission(monitor)
- options：选项，必须使用key或者key=value的语法指定，可用的options如下
- -l：（可选）打印java.util.concurrent锁（BOLEAN，false）
示例：
可以看到下面的效果和jstack pid的效果一样
C:\\Users\\86136>jcmd -l 3808 sun.tools.jcmd.JCmd -l 4104 org.jetbrains.jps.cmdline.Launcher D:/JetBrains/idea20190303/lib/netty-codec-4.1.41.Final.jar;D:/JetBrains/idea20190303/plugins/java/lib/maven-repository-metadata-3.3.9.jar;D:/JetBrains/idea20190303/plugins/java/lib/aether-impl-1.1.0.jar;D:/JetBrains/idea20190303/lib/jdom.jar;D:/JetBrains/idea20190303/plugins/java/lib/commons-lang3-3.4.jar;D:/JetBrains/idea20190303/plugins/java/lib/maven-model-3.3.9.jar;D:/JetBrains/idea20190303/plugins/java/lib/jps-builders-6.jar;D:/JetBrains/idea20190303/plugins/java/lib/plexus-component-annotations-1.6.jar;D:/JetBrains/idea20190303/plugins/java/lib/aether-transport-file-1.1.0.jar;D:/JetBrains/idea20190303/lib/httpcore-4.4.12.jar;D:/JetBrains/idea20190303/lib/commons-logging-1.2.jar;D:/JetBrains/idea20190303/plugins/java/lib/aether-dependency-resolver.jar;D:/JetBrains/idea20190303/plugins/java/lib/plexus-utils-3.0.22.jar;D:/JetBrains/idea20190303/lib/jna.jar;D:/JetBrains/idea20190303/lib/platform-api.jar;D:/JetBrains/idea20190303/plugins/java/lib/maven-aether-provider-3.3.9 7000 9592 org.jetbrains.idea.maven.server.RemoteMavenServer 14796 com.kgf.kgfjavalearning2021.jvm.JstackLockTest C:\\Users\\86136>jcmd 14796 Thread.print -l 14796: 2021-12-01 21:26:30 Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.51-b03 mixed mode): "DestroyJavaVM" #14 prio=5 os_prio=0 tid=0x0000000002ed4000 nid=0x2044 waiting on condition [0x0000000000000000] java.lang.Thread.State: RUNNABLE Locked ownable synchronizers: - None "Thread-1" #13 prio=5 os_prio=0 tid=0x000000001f929800 nid=0xc2c waiting for monitor entry [0x00000000208ff000] java.lang.Thread.State: BLOCKED (on object monitor) at com.kgf.kgfjavalearning2021.jvm.JstackLockTest$2.run(JstackLockTest.java:50) - waiting to lock <0x000000076b92cbf8> (a java.lang.StringBuilder) - locked <0x000000076b92cc40> (a java.lang.StringBuilder) at java.lang.Thread.run(Thread.java:745) Locked ownable synchronizers: - None "Thread-0" #12 prio=5 os_prio=0 tid=0x000000001f8de800 nid=0x21d0 waiting for monitor entry [0x00000000207ff000] java.lang.Thread.State: BLOCKED (on object monitor) at com.kgf.kgfjavalearning2021.jvm.JstackLockTest$1.run(JstackLockTest.java:26) - waiting to lock <0x000000076b92cc40> (a java.lang.StringBuilder) - locked <0x000000076b92cbf8> (a java.lang.StringBuilder) at java.lang.Thread.run(Thread.java:745) Locked ownable synchronizers: - None "Service Thread" #11 daemon prio=9 os_prio=0 tid=0x000000001e5c9000 nid=0x3b70 runnable [0x0000000000000000] java.lang.Thread.State: RUNNABLE Locked ownable synchronizers: - None "C1 CompilerThread3" #10 daemon prio=9 os_prio=2 tid=0x000000001e5c1000 nid=0x38b4 waiting on condition [0x0000000000000000] java.lang.Thread.State: RUNNABLE Locked ownable synchronizers: - None "C2 CompilerThread2" #9 daemon prio=9 os_prio=2 tid=0x000000001e5c0000 nid=0xac0 waiting on condition [0x0000000000000000] java.lang.Thread.State: RUNNABLE Locked ownable synchronizers: - None "C2 CompilerThread1" #8 daemon prio=9 os_prio=2 tid=0x000000001e5bf800 nid=0x2930 waiting on condition [0x0000000000000000] java.lang.Thread.State: RUNNABLE Locked ownable synchronizers: - None "C2 CompilerThread0" #7 daemon prio=9 os_prio=2 tid=0x000000001e5be800 nid=0x3724 waiting on condition [0x0000000000000000] java.lang.Thread.State: RUNNABLE Locked ownable synchronizers: - None "Monitor Ctrl-Break" #6 daemon prio=5 os_prio=0 tid=0x000000001f822800 nid=0x39c4 runnable [0x00000000200ff000] 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 <0x000000076b98f038> (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 <0x000000076b98f038> (a java.io.InputStreamReader) at java.io.BufferedReader.readLine(BufferedReader.java:389) at com.intellij.rt.execution.application.AppMainV2$1.run(AppMainV2.java:64) Locked ownable synchronizers: - None "Attach Listener" #5 daemon prio=5 os_prio=2 tid=0x000000001e312000 nid=0x2d70 waiting on condition [0x0000000000000000] java.lang.Thread.State: RUNNABLE Locked ownable synchronizers: - None "Signal Dispatcher" #4 daemon prio=9 os_prio=2 tid=0x000000001e311800 nid=0x350c runnable [0x0000000000000000] java.lang.Thread.State: RUNNABLE Locked ownable synchronizers: - None "Finalizer" #3 daemon prio=8 os_prio=1 tid=0x000000001cbbd000 nid=0x2fc0 in Object.wait() [0x000000001f5ff000] java.lang.Thread.State: WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x000000076b586f58> (a java.lang.ref.ReferenceQueue$Lock) at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:143) - locked <0x000000076b586f58> (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: - None "Reference Handler" #2 daemon prio=10 os_prio=2 tid=0x000000001cbbb800 nid=0x3abc in Object.wait() [0x000000001f4fe000] java.lang.Thread.State: WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x000000076b586998> (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 <0x000000076b586998> (a java.lang.ref.Reference$Lock) Locked ownable synchronizers: - None "VM Thread" os_prio=2 tid=0x000000001e282800 nid=0x10c0 runnable "GC task thread#0 (ParallelGC)" os_prio=0 tid=0x0000000002ee9800 nid=0xbd4 runnable "GC task thread#1 (ParallelGC)" os_prio=0 tid=0x0000000002eeb000 nid=0xdd4 runnable "GC task thread#2 (ParallelGC)" os_prio=0 tid=0x0000000002eed000 nid=0x35e0 runnable "GC task thread#3 (ParallelGC)" os_prio=0 tid=0x0000000002eee800 nid=0x2de8 runnable "GC task thread#4 (ParallelGC)" os_prio=0 tid=0x0000000002ef0800 nid=0x2888 runnable "GC task thread#5 (ParallelGC)" os_prio=0 tid=0x0000000002ef2000 nid=0x36c8 runnable "GC task thread#6 (ParallelGC)" os_prio=0 tid=0x0000000002ef6000 nid=0x1350 runnable "GC task thread#7 (ParallelGC)" os_prio=0 tid=0x0000000002ef7000 nid=0xec4 runnable "GC task thread#8 (ParallelGC)" os_prio=0 tid=0x0000000002ef8800 nid=0x13d8 runnable "GC task thread#9 (ParallelGC)" os_prio=0 tid=0x0000000002ef9800 nid=0x31e8 runnable "VM Periodic Task Thread" os_prio=2 tid=0x000000001e5c9800 nid=0x249c waiting on condition JNI global references: 33 Found one Java-level deadlock: ============================= "Thread-1": waiting to lock monitor 0x0000000002fce708 (object 0x000000076b92cbf8, a java.lang.StringBuilder), which is held by "Thread-0" "Thread-0": waiting to lock monitor 0x0000000002fcd268 (object 0x000000076b92cc40, a java.lang.StringBuilder), which is held by "Thread-1" Java stack information for the threads listed above: =================================================== "Thread-1": at com.kgf.kgfjavalearning2021.jvm.JstackLockTest$2.run(JstackLockTest.java:50) - waiting to lock <0x000000076b92cbf8> (a java.lang.StringBuilder) - locked <0x000000076b92cc40> (a java.lang.StringBuilder) at java.lang.Thread.run(Thread.java:745) "Thread-0": at com.kgf.kgfjavalearning2021.jvm.JstackLockTest$1.run(JstackLockTest.java:26) - waiting to lock <0x000000076b92cc40> (a java.lang.StringBuilder) - locked <0x000000076b92cbf8> (a java.lang.StringBuilder) at java.lang.Thread.run(Thread.java:745) Found 1 deadlock. C:\\Users\\86136>
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