Threads Needles Stacks Heaps - Java edition
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The thread dump identifies the application and JVM threads present in the JVM at the time of the dump. It provides information on each thread's state, stack trace and timing details. It also includes a summary of JVM heap utilization broken down by generation. This information can help identify potential blocking issues, performance bottlenecks or memory leaks in the application.
![-XX are not stable and are subject to change without notice
!
Boolean
-XX:+<option> or -XX:-<option>
!
Numeric
-XX:<option>=<number>[unit]
Unit:‘k’,‘K’,‘m’,‘M’,‘g’,‘G’ - 32768 or 32k
!
String
-XX:<option>=<string>
Flags](https://image.slidesharecdn.com/threadsneedlesstacksheaps-140316111049-phpapp02/85/Threads-Needles-Stacks-Heaps-Java-edition-31-320.jpg)
![Thread Dump
"main" prio=5 tid=0x0000000101028800 nid=0x507 runnable [0x00007fff5fbfd000]
java.lang.Thread.State: RUNNABLE
at org.eclipse.swt.internal.cocoa.OS.objc_msgSend_bool(Native Method)
at org.eclipse.swt.internal.cocoa.NSRunLoop.runMode(NSRunLoop.java:42)
at org.eclipse.swt.widgets.Display.sleep(Display.java:4565)
at org.eclipse.ui.application.WorkbenchAdvisor.eventLoopIdle(WorkbenchAdvisor.java:364)
at org.eclipse.ui.internal.ide.application.IDEWorkbenchAdvisor.eventLoopIdle(IDEWorkbenchAdvisor.java:917)
at org.eclipse.ui.internal.Workbench$3.eventLoopIdle(Workbench.java:459)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$9.run(PartRenderingEngine.java:1026)
at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:916)
at org.eclipse.e4.ui.internal.workbench.E4Workbench.createAndRunUI(E4Workbench.java:86)
at org.eclipse.ui.internal.Workbench$5.run(Workbench.java:585)
at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:540)
at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:149)
at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:124)
at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:196)
at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:110)
at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:79)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:353)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:180)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:629)
at org.eclipse.equinox.launcher.Main.basicRun(Main.java:584)
at org.eclipse.equinox.launcher.Main.run(Main.java:1438)](https://image.slidesharecdn.com/threadsneedlesstacksheaps-140316111049-phpapp02/85/Threads-Needles-Stacks-Heaps-Java-edition-48-320.jpg)
![Thread Dump
"C2 CompilerThread1" daemon prio=5 tid=0x0033 nid=0x6703 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
!
"C2 CompilerThread0" daemon prio=5 tid=0x0011 nid=0x6503 waiting on condition [0x0000000000]
java.lang.Thread.State: RUNNABLE
!
"Signal Dispatcher" daemon prio=5 tid=0x0022 nid=0x6303 runnable [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
!
"Finalizer" daemon prio=5 tid=0x0044 nid=0x5f03 in Object.wait() [0x000000010b88b000]
java.lang.Thread.State:WAITING (on object monitor)
!
"Reference Handler" daemon prio=5 tid=0x0055 nid=0x5d03 in Object.wait() [0x000000010b788000]
java.lang.Thread.State:WAITING (on object monitor)
!
"VM Thread" prio=5 tid=0x0066 nid=0x5b03 runnable
!
"GC task thread#0 (ParallelGC)" prio=5 tid=0x000000010102d000 nid=0x5303 runnable
!
"GC task thread#1 (ParallelGC)" prio=5 tid=0x0000000101038800 nid=0x5503 runnable
!
"GC task thread#2 (ParallelGC)" prio=5 tid=0x0000000101039000 nid=0x5703 runnable
!
"GC task thread#3 (ParallelGC)" prio=5 tid=0x0000000101039800 nid=0x5903 runnable
!
"VM Periodic Task Thread" prio=5 tid=0x0000000101058000 nid=0x6b03 waiting on condition
In general theVM thread is in one of three states: waiting to execute aVM operation, synchronizing all threads in preparation for aVM
operation, or executing aVM operation. If you suspect that a hang is a HotSpotVM bug rather than an application or class library
deadlock, then pay special attention to theVM thread.](https://image.slidesharecdn.com/threadsneedlesstacksheaps-140316111049-phpapp02/85/Threads-Needles-Stacks-Heaps-Java-edition-50-320.jpg)
![Thread Dump
“Thread I" prio=5 tid=0x0100 nid=0x1ef runnable [0x01acff]
java.lang.Thread.State: RUNNABLE
!
“Thread 3" prio=5 tid=0x0300 nid=0x3dd in Object.wait() [0x0366]
java.lang.Thread.State:TIMED_WAITING (on object monitor)
!
“Thread 4" prio=5 tid=0x0400 nid=0x4ab in Object.wait() [0x0477]
java.lang.Thread.State:WAITING (on object monitor)
!
“Thread 5" prio=5 tid=0x0500 nid=0x5bd waiting for monitor entry [0x0523]
java.lang.Thread.State: BLOCKED (on object monitor)
!
“Thread 2" prio=5 tid=0x0200 nid=0x2ef waiting on condition [0x02b8]
java.lang.Thread.State:TIMED_WAITING (sleeping)
!
“Thread 6" prio=5 tid=0x0600 nid=0x6ef waiting on condition [0x06b8]
java.lang.Thread.State: TIMED_WAITING (sleeping)](https://image.slidesharecdn.com/threadsneedlesstacksheaps-140316111049-phpapp02/85/Threads-Needles-Stacks-Heaps-Java-edition-54-320.jpg)
Threads Needles Stacks Heaps - Java edition
- 1. ! ! ! Threads, Needles, Stacks, Heaps DevNexus, 2014 Ovidiu Dimulescu ! @odimulescu www.odimulescu.com
- 2. The opinions and views expressed in this talk are my own, and do not necessarily reflect the opinions or views of my employer.
- 3. • Landscape • Flags • Threads • OOME • Questions? Agenda
- 4. • Oracle HotSpot • OpenJDK HotSpot • Oracle JRockit * • IBM JVM • Azul Systems Zing JVM * • Waratek CloudVM * Landscape - JVMs
- 5. • Why is the application slow? • Why does the application have hiccups? • Why is CPU pegged? • Why are we running out of memory? • … • Why _______ ? Landscape - Pain points
- 7. App Servers Message Queues Caches Schedulers Workers Data Stores Clients
- 8. #### Assumption is the mother of all F***UPS! - Travis Dane
- 9. #### Measure Anything, Measure Everything ! “ If Engineering at Etsy has a religion, it’s the Church of Graphs. If it moves, we track it …” http://codeascraft.com/2011/02/15/measure-anything-measure-everything/
- 10. * Images Credit: Wikimedia Commons
- 11. • Complex apps architecture and environments • Insufficient historical data • Weak inter-systems correlation • Platforms disparity • No one size fits all • Folklore, outdated information • High barrier to entry for effective diagnostics Landscape - Challenges
- 12. The JVM
- 13. JPDA - Platform Debugger Architecture * http://docs.oracle.com/javase/6/docs/technotes/guides/jpda/architecture.html
- 14. JPDA - Platform Debugger Architecture * http://docs.oracle.com/javase/6/docs/technotes/guides/jpda/architecture.html
- 15. • Profiling, debugging, monitoring, thread analysis, coverage analysis, etc. JVM TI - JVM Tool Interface
- 16. • Profiling, debugging, monitoring, thread analysis, coverage analysis, etc. ! • Native Agents - Full » -agentlib:<agent-lib-name>=<options> » -agentpath:<path-to-agent>=<options> » hprof, jdwp agents included JVM TI - JVM Tool Interface
- 17. • Profiling, debugging, monitoring, thread analysis, coverage analysis, etc. ! • Native Agents - Full » -agentlib:<agent-lib-name>=<options> » -agentpath:<path-to-agent>=<options> » hprof, jdwp agents included ! • Java Agents - Instrumentation only (java.lang.instrument.*) » -javaagent:agent-name.jar » multiple supported, management-agent.jar provided JVM TI - JVM Tool Interface
- 18. JVM TI - JVM Tool Interface TI Agent I JVM TI Agent II event action event action TI Client Attach API load agent
- 19. JMX - Java Management Extensions MBeanServer Standard MBeans Dynamic MBeans MXBeans Connector Connector Adaptor Adaptor Probes Agent Clients Remote Management JMX Console Custom Console RMI HTTP Browser HTTP SNMP SNMP J V M
- 20. JMX - Java Management Extensions MBeanServer Standard MBeans Dynamic MBeans MXBeans Connector Connector Adaptor Adaptor Probes Agent Clients Remote Management JMX Console Custom Console RMI HTTP Browser HTTP SNMP SNMP J V M
- 21. JMX - Java Management Extensions http://docs.oracle.com/javase/7/docs/api/java/lang/management/package-summary.html
- 22. JMX - Java Management Extensions Explicit ! -Dcom.sun.management.jmxremote -Dcom.sun.management.jmxremote.authenticate=false -Dcom.sun.management.jmxremote.port=1234 -Dcom.sun.management.jmxremote.ssl=false -Dcom.sun.management.jmxremote.password.file=/path/to/pw/file -Dcom.sun.management.jmxremote.access.file=/path/to/access/file -Djava.rmi.server.hostname=<resolvable_from_clients> ! Attach API ! Unless -XX:+DisableAttachMechanism
- 23. JMX - Java Management Extensions • De facto standard • Wide support • RMI not firewall friendly, dynamic ports • RMI connector heavy, Observer effect • MBeans need to behave
- 24. • jcmd (JDK 7+) • jinfo • jhat • jmap • jps • jstat / jstatd • jstack HotSpot - Command Line Tools http://docs.oracle.com/javase/7/docs/webnotes/tsg/TSG-VM/html/tooldescr.html
- 25. • jhat • JConsole • VisualVM • MissionControl (JDK >= 7u40) HotSpot - Graphical Tools
- 26. Vendor Tools - Sample set
- 27. Heap Analysers ! » MAT » Heapster » HeapAudit Open Source Tools GC Visualization ! » VisualVM » GCViewer » GCHisto » gcviz JMX Clients ! » MC5J » VisualVM » jmxterm » CRaSH Code Libraries * ! » Coda Hale Metrics » Javalution » Trove » FastUtil
- 28. * Image Credit: Wikimedia Commons
- 30. -X are non-standard, not guaranteed to be supported on all VM implementations, and are subject to change without notice in subsequent releases of the JDK. ! $ java -X … -Xloggc:<file> log GC status to a file with time stamps -Xms<size> set initial Java heap size -Xmx<size> set maximum Java heap size -Xss<size> set java thread stack size -Xprof output cpu profiling data … Flags
- 31. -XX are not stable and are subject to change without notice ! Boolean -XX:+<option> or -XX:-<option> ! Numeric -XX:<option>=<number>[unit] Unit:‘k’,‘K’,‘m’,‘M’,‘g’,‘G’ - 32768 or 32k ! String -XX:<option>=<string> Flags
- 32. $ java -XX:+PrintFlagsInitial -version $ java -XX:+PrintFlagsFinal -version $ java -XX:+PrintCommandLineFlags -version ! • product - An officially supported, internal JVM option • rw - Dynamically writable • C1 - Client JIT Compiler • C2 - Server JIT Compiler • pd - Platform Dependent • lp64 - 64bitVM only • manageable - Externally defined and dynamically writable • diagnostic -VM debugging • experimental - Not officially supported ! -XX:+UnlockExperimentalVMOptions -XX:+UnlockDiagnosticVMOptions Flags
- 33. • ms • mx • PermSize • MaxPermSize • NewSize • MaxNewSize • NewRatio • UseCompressedOps • HeapDumpOnOutOfMemoryError • HeapDumpPath Flags - Memory
- 34. Flags - GC Logging • verbose:gc • loggc • PrintGCDetails • PrintGCTimeStamps • PrintGCDateStamps • UseGCLogFileRotation • NumberOfGCLogFiles=10 • GCLogFileSize=50M • PrintTenuringDistribution • PrintGCApplicationStoppedTime
- 35. Flags - GC • verbose:class • TraceClassLoading • TraceClassUnloading • TraceClassResolution • UseParallelGC • UseParallelOldGC • UseParNewGC • UseConcMarkSweepGC • GCTimeLimit • GCHeapFreeLimit
- 37. Flags - Demo
- 38. * Image Credit: Wikimedia Commons
- 42. Threads Type Regular Daemon Name Automatic Custom * Parent Group Not Null* Priority MIN - NORM - MAX
- 43. Threads Type Regular Daemon Name Automatic Custom * Parent Group Not Null* Priority MIN - NORM - MAX State Thread.State
- 45. Thread Dump $ jstack <pid> $ jcmd <pid> Thread.print (JDK 7+) ! Output to terminal ! $ kill -3 <pid> or kill -SIGQUIT <pid> ! Outputs to JVM’s stdout ! JMX ! VisualVM, JConsole, etc.
- 46. Thread Dump » Dump identifier ! 2014-02-15 15:05:42 Full thread dump Java HotSpot(TM) 64-Bit Server VM (24.45-b08 mixed mode)
- 47. Thread Dump » Dump identifier ! » Application Threads !
- 48. Thread Dump "main" prio=5 tid=0x0000000101028800 nid=0x507 runnable [0x00007fff5fbfd000] java.lang.Thread.State: RUNNABLE at org.eclipse.swt.internal.cocoa.OS.objc_msgSend_bool(Native Method) at org.eclipse.swt.internal.cocoa.NSRunLoop.runMode(NSRunLoop.java:42) at org.eclipse.swt.widgets.Display.sleep(Display.java:4565) at org.eclipse.ui.application.WorkbenchAdvisor.eventLoopIdle(WorkbenchAdvisor.java:364) at org.eclipse.ui.internal.ide.application.IDEWorkbenchAdvisor.eventLoopIdle(IDEWorkbenchAdvisor.java:917) at org.eclipse.ui.internal.Workbench$3.eventLoopIdle(Workbench.java:459) at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$9.run(PartRenderingEngine.java:1026) at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332) at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:916) at org.eclipse.e4.ui.internal.workbench.E4Workbench.createAndRunUI(E4Workbench.java:86) at org.eclipse.ui.internal.Workbench$5.run(Workbench.java:585) at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332) at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:540) at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:149) at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:124) at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:196) at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:110) at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:79) at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:353) at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:180) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:606) at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:629) at org.eclipse.equinox.launcher.Main.basicRun(Main.java:584) at org.eclipse.equinox.launcher.Main.run(Main.java:1438)
- 49. Thread Dump » Dump identifier ! » Application Threads ! » VM Threads
- 50. Thread Dump "C2 CompilerThread1" daemon prio=5 tid=0x0033 nid=0x6703 waiting on condition [0x0000000000000000] java.lang.Thread.State: RUNNABLE ! "C2 CompilerThread0" daemon prio=5 tid=0x0011 nid=0x6503 waiting on condition [0x0000000000] java.lang.Thread.State: RUNNABLE ! "Signal Dispatcher" daemon prio=5 tid=0x0022 nid=0x6303 runnable [0x0000000000000000] java.lang.Thread.State: RUNNABLE ! "Finalizer" daemon prio=5 tid=0x0044 nid=0x5f03 in Object.wait() [0x000000010b88b000] java.lang.Thread.State:WAITING (on object monitor) ! "Reference Handler" daemon prio=5 tid=0x0055 nid=0x5d03 in Object.wait() [0x000000010b788000] java.lang.Thread.State:WAITING (on object monitor) ! "VM Thread" prio=5 tid=0x0066 nid=0x5b03 runnable ! "GC task thread#0 (ParallelGC)" prio=5 tid=0x000000010102d000 nid=0x5303 runnable ! "GC task thread#1 (ParallelGC)" prio=5 tid=0x0000000101038800 nid=0x5503 runnable ! "GC task thread#2 (ParallelGC)" prio=5 tid=0x0000000101039000 nid=0x5703 runnable ! "GC task thread#3 (ParallelGC)" prio=5 tid=0x0000000101039800 nid=0x5903 runnable ! "VM Periodic Task Thread" prio=5 tid=0x0000000101058000 nid=0x6b03 waiting on condition In general theVM thread is in one of three states: waiting to execute aVM operation, synchronizing all threads in preparation for aVM operation, or executing aVM operation. If you suspect that a hang is a HotSpotVM bug rather than an application or class library deadlock, then pay special attention to theVM thread.
- 51. Thread Dump » Dump identifier ! » Application Threads ! » VM Threads ! » JNI References Count ! JNI global references: 759
- 52. Thread Dump » Dump identifier ! » Application Threads ! » VM Threads ! » JNI References Count ! » Heap Utilization Summary *
- 53. Thread Dump PSYoungGen total 75776K, used 69708K [0x07f55, 0x07fb48, 0x08) eden space 75264K, 92% used [0x07f550,0x07f98fb028,0x07f9e8) from space 512K, 18% used [0x07fa18,0x07fa1980,0x07fa20) to space 11264K, 0% used [0x07fa98,0x07fa98,0x07fb48) ! ParOldGen total 59392K, used 46432K [0x07e0, 0x07e3a0, 0x07f550) object space 59392K, 78% used [0x07e0,0x07e2d58270,0x07e3a0) ! PSPermGen total 71680K, used 47149K [0x07d0, 0x07d460, 0x07e0) object space 71680K, 65% used [0x07d0,0x07d2e0b6c8,0x07d460)
- 54. Thread Dump “Thread I" prio=5 tid=0x0100 nid=0x1ef runnable [0x01acff] java.lang.Thread.State: RUNNABLE ! “Thread 3" prio=5 tid=0x0300 nid=0x3dd in Object.wait() [0x0366] java.lang.Thread.State:TIMED_WAITING (on object monitor) ! “Thread 4" prio=5 tid=0x0400 nid=0x4ab in Object.wait() [0x0477] java.lang.Thread.State:WAITING (on object monitor) ! “Thread 5" prio=5 tid=0x0500 nid=0x5bd waiting for monitor entry [0x0523] java.lang.Thread.State: BLOCKED (on object monitor) ! “Thread 2" prio=5 tid=0x0200 nid=0x2ef waiting on condition [0x02b8] java.lang.Thread.State:TIMED_WAITING (sleeping) ! “Thread 6" prio=5 tid=0x0600 nid=0x6ef waiting on condition [0x06b8] java.lang.Thread.State: TIMED_WAITING (sleeping)
- 55. Threads - Demo
- 56. OOEM
- 57. Exception in thread "main" java.lang.OutOfMemoryError: <Reason> OOEM - Flavors
- 58. • Java heap space OOEM - Flavors
- 59. • Java heap space • PermGen space OOEM - Flavors
- 60. • Java heap space • PermGen space • GC overhead limit exceeded OOEM - Flavors
- 61. • Java heap space • PermGen space • GC overhead limit exceeded • unable to create new native thread OOEM - Flavors
- 62. • Java heap space • PermGen space • GC overhead limit exceeded • unable to create new native thread • Requested array size exceedsVM limit • request <size> bytes for <reason>. Out of swap space? • <reason> <stack trace> (Native method) • Direct buffer memory OOEM - Flavors
- 63. Guilty until proven innocent * Image Credit: http://www.sodahead.com/living/which-do-you-think-is-more-important-in-the-running-of-a-society-garbage-collector-or-surgeon/question-3564735/
- 64. • Sizing » Heap Areas (Eden, Old, PermGen, etc.) » Tenuring Threshold » Thread Stack ! • Collectors choice » Type (Parallel, ParallelOld, CMS, G1) » Options (# of threads, etc.) OOEM - JVM Configuration
- 65. • Containers » Classloaders leaks ! • Frameworks » Reflection » Dynamic proxies OOEM - Application Runtime
- 66. • Objects structure overhead ! • Collections waste » Fill ratio consideration » Never shrink » Up to 2 x expansion algorithms ! • Use of Finalizers, 2 x GC cycles OOEM - Application
- 67. Heap Demo
- 68. • JVM Fundamentals • Tools of the trade • Instrument the app • Telemetry • Culture Summary