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JDK Power Tools

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Presented at GeekOut 2013. …

Presented at GeekOut 2013.
Original available at: https://github.com/thobe/presentations/tree/master/GeekOut2013

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  • 1. JDK Power Tools an overview of fun and useful tools the JDK already provides you with Tobias Lindaaker Software Developer @ Neo Technology twitter:! @thobe / @neo4j / #neo4j email:! tobias@neotechnology.com web:! http://neo4j.org/ web:! http://thobe.org/
  • 2. The Tools ๏java.lang.instrument ๏Java agents ๏Java Debugging Interface ๏JVMTI heap introspection ๏JVMTI frame introspection 2
  • 3. java.lang.instrument 3
  • 4. java.lang.instrument.Instrumentation ๏The “missing” sizeof() operation: •long getObjectSize( Object ) ๏Inspecting loaded classes: •Class[] getAllLoadedClasses() •Class[] getInitiatedClasses( ClassLoader ) ๏Transforming classes: •redefineClasses( ClassDefinition(Class, byte[])... ) •addTransformer( ClassFileTransformer ) ‣byte[] transform( ClassLoader, name, Class, byte[] ) •retransformClasses(Class...) •setNativeMethodPrefix( ClassFileTransformer, String ) 4
  • 5. public static void premain( String agentArgs, Instrumentation inst) 5 ๏java ... -javaagent:<jarfile>[=options] ๏Instrumentation parameter is optional in the signature ๏META-INF/MANIFEST.MF: •Premain-Class [required; qualified classname of premain class] •Boot-Class-Path [optional; class path] •Can-Redefine-Classes [optional; true/false - request capability] •Can-Retransform-Classes [optional; true/false - request capability] •Can-Set-Native-Method-Prefix [optional; true/false - request capability]
  • 6. Java agents 6
  • 7. public static void agentmain( String agentArgs, Instrumentation inst) 7 ๏Executed when the agent attaches to an already running JVM ๏Instrumentation parameter is optional in the signature ๏META-INF/MANIFEST.MF: •Agentmain-Class +the same optional parameters as for premain(): +Boot-Class-Path +Can-Redefine-Classes +Can-Retransform-Classes +Can-Set-Native-Method-Prefix ๏Requires support for loading agents in the JVM ๏Allows to add code to the JVM after-the-fact
  • 8. The Use Case: add code live ๏Provide statically accessible entry point into your app ๏From here extend the app with the code loaded by the agent ๏Used by the JDK, when attaching with jconsole through PID 8
  • 9. com.sun.tools.attach ๏com.sun.tools.attach.VirtualMachine •Represents a JVM process •static methods providing entry points for: ‣attaching to a JVM by process id ‣listing all running JVM processes (like jps) ๏Example (from the docs, simplified from jconsole source code): // attach to target VM VirtualMachine vm = VirtualMachine.attach( "1337" ); // get system properties in target VM Properties props = vm.getSystemProperties(); // construct path to management agent String agent = props.getProperty( "java.home" ) + File.separator + "lib" + File.separator + "management-agent.jar"; // load agent into target VM, spcifying parameters for the agent vm.loadAgent( agent, "com.sun.management.jmxremote.port=5000" ); // done - detach vm.detach(); 9
  • 10. Tricks: Registry-less RMI ๏RMI Registry just provides serialized objects specifying: •Implemented Remote interfaces •How to reach the actual object (host+port+id) ๏You can serialize the object yourself and pass it as the string parameter to an agent ๏Now your agent has a talkback channel to the process that spawned it 10
  • 11. code.sample(); 11 http://github.com/thobe/java-agent
  • 12. Java Debugging Interface 12 Building an interactive debugger is HARD, but that isn’t the only thing you can do with the JDI. A Scriptable debugger is much easier to build.
  • 13. SubprocessTestRunner 13 ๏Runs a JUnit test case in a sub process ๏Host process connects to the sub process with JDI ๏Define breakpoints for the code under test ๏Useful for triggering certain ordering between threads •Triggering race conditions ๏Used at Neo Technology for Concurrency Regression Tests •Prefer refactoring to allow testing concurrency, but that isn’t always the appropriate short term solution
  • 14. Simple example @RunWith(SubprocessTestRunner.class) public class SampleTest { @Debugger.Using(BreakPoints.class) @Test public void shouldHandleRaceCondition() { new Sample().entryPoint(); } static class BreakPoints extends Debugger { List<Integer> loopVariables = new ArrayList<Integer>(); { enable( "handle_someMethod" ); } @Handler(on=ENTRY,type=Sample.class,method="someMethod") void handle_someMethod() { enable( "handle_loopBody" ); } @Handler(on=ENTRY,type=Sample.class,method="loopBody") void handle_loopBody(){ loopVariables.add( frame( 1 ).getInt( "i" ) ); } @Override protected void finish() { assertEquals( asList( 1, 2, 3, 4 ), loopVariables ); } } } 14
  • 15. Simple example @RunWith(SubprocessTestRunner.class) public class SampleTest { @Debugger.Using(BreakPoints.class) @Test public void shouldHandleRaceCondition() { new Sample().entryPoint(); } static class BreakPoints extends Debugger { List<Integer> loopVariables = new ArrayList<Integer>(); { enable( "handle_someMethod" ); } @Handler(on=ENTRY,type=Sample.class,method="someMethod") void handle_someMethod() { enable( "handle_loopBody" ); } @Handler(on=ENTRY,type=Sample.class,method="loopBody") void handle_loopBody(){ loopVariables.add( frame( 1 ).getInt( "i" ) ); } @Override protected void finish() { assertEquals( asList( 1, 2, 3, 4 ), loopVariables ); } } } 14 public class Sample { public void entryPoint() { for ( int i = 0; i < 5; i++ ) { loopBody(); someMethod(); } } private void someMethod() { /* do nothing */ } private void loopBody() { /* do nothing */ } }
  • 16. Simple example @RunWith(SubprocessTestRunner.class) public class SampleTest { @Debugger.Using(BreakPoints.class) @Test public void shouldHandleRaceCondition() { new Sample().entryPoint(); } static class BreakPoints extends Debugger { List<Integer> loopVariables = new ArrayList<Integer>(); { enable( "handle_someMethod" ); } @Handler(on=ENTRY,type=Sample.class,method="someMethod") void handle_someMethod() { enable( "handle_loopBody" ); } @Handler(on=ENTRY,type=Sample.class,method="loopBody") void handle_loopBody(){ loopVariables.add( frame( 1 ).getInt( "i" ) ); } @Override protected void finish() { assertEquals( asList( 1, 2, 3, 4 ), loopVariables ); } } } 14 { enable( "handle_someMethod" ); }
  • 17. Simple example @RunWith(SubprocessTestRunner.class) public class SampleTest { @Debugger.Using(BreakPoints.class) @Test public void shouldHandleRaceCondition() { new Sample().entryPoint(); } static class BreakPoints extends Debugger { List<Integer> loopVariables = new ArrayList<Integer>(); { enable( "handle_someMethod" ); } @Handler(on=ENTRY,type=Sample.class,method="someMethod") void handle_someMethod() { enable( "handle_loopBody" ); } @Handler(on=ENTRY,type=Sample.class,method="loopBody") void handle_loopBody(){ loopVariables.add( frame( 1 ).getInt( "i" ) ); } @Override protected void finish() { assertEquals( asList( 1, 2, 3, 4 ), loopVariables ); } } } 14 @Handler(on=ENTRY,type=Sample.class,method="someMethod") void handle_someMethod() { enable( "handle_loopBody" ); }
  • 18. Simple example @RunWith(SubprocessTestRunner.class) public class SampleTest { @Debugger.Using(BreakPoints.class) @Test public void shouldHandleRaceCondition() { new Sample().entryPoint(); } static class BreakPoints extends Debugger { List<Integer> loopVariables = new ArrayList<Integer>(); { enable( "handle_someMethod" ); } @Handler(on=ENTRY,type=Sample.class,method="someMethod") void handle_someMethod() { enable( "handle_loopBody" ); } @Handler(on=ENTRY,type=Sample.class,method="loopBody") void handle_loopBody(){ loopVariables.add( frame( 1 ).getInt( "i" ) ); } @Override protected void finish() { assertEquals( asList( 1, 2, 3, 4 ), loopVariables ); } } } 14 @Handler(on=ENTRY,type=Sample.class,method="loopBody") void handle_loopBody(){ loopVariables.add( frame( 1 ).getInt( "i" ) ); }
  • 19. Simple example @RunWith(SubprocessTestRunner.class) public class SampleTest { @Debugger.Using(BreakPoints.class) @Test public void shouldHandleRaceCondition() { new Sample().entryPoint(); } static class BreakPoints extends Debugger { List<Integer> loopVariables = new ArrayList<Integer>(); { enable( "handle_someMethod" ); } @Handler(on=ENTRY,type=Sample.class,method="someMethod") void handle_someMethod() { enable( "handle_loopBody" ); } @Handler(on=ENTRY,type=Sample.class,method="loopBody") void handle_loopBody(){ loopVariables.add( frame( 1 ).getInt( "i" ) ); } @Override protected void finish() { assertEquals( asList( 1, 2, 3, 4 ), loopVariables ); } } } 14 @Override protected void finish() { assertEquals( asList( 1, 2, 3, 4 ), loopVariables ); }
  • 20. Simple example @RunWith(SubprocessTestRunner.class) public class SampleTest { @Debugger.Using(BreakPoints.class) @Test public void shouldHandleRaceCondition() { new Sample().entryPoint(); } static class BreakPoints extends Debugger { List<Integer> loopVariables = new ArrayList<Integer>(); { enable( "handle_someMethod" ); } @Handler(on=ENTRY,type=Sample.class,method="someMethod") void handle_someMethod() { enable( "handle_loopBody" ); } @Handler(on=ENTRY,type=Sample.class,method="loopBody") void handle_loopBody(){ loopVariables.add( frame( 1 ).getInt( "i" ) ); } @Override protected void finish() { assertEquals( asList( 1, 2, 3, 4 ), loopVariables ); } } } 14
  • 21. code.samples(); 15 https://github.com/thobe/subprocess-testing
  • 22. JVMTI frame introspection 16
  • 23. Frame introspection ๏Native interface (JVMTI) ๏Abilities: •Get method and instruction offset for each element on stack •Force early return from method •Pop frame and re-run method •Get local variable from call stack •Get notification when frame is popped (method is exited) (Forcing a frame to be popped does not trigger the event) 17
  • 24. Dynamic access to local variables public @Test void sampleOfAccessingLiveCallFrame() { int anInt = 4; // random number - by dice String aString = "some string value"; 18
  • 25. Dynamic access to local variables public @Test void sampleOfAccessingLiveCallFrame() { int anInt = 4; // random number - by dice String aString = "some string value"; // get the tool ToolingInterface tools = ToolingInterface.getToolingInterface(); 18
  • 26. Dynamic access to local variables public @Test void sampleOfAccessingLiveCallFrame() { int anInt = 4; // random number - by dice String aString = "some string value"; // get the tool ToolingInterface tools = ToolingInterface.getToolingInterface(); // get the frame CallFrame myFrame = tools.getCallFrame( 0 ); 18
  • 27. Dynamic access to local variables public @Test void sampleOfAccessingLiveCallFrame() { int anInt = 4; // random number - by dice String aString = "some string value"; // get the tool ToolingInterface tools = ToolingInterface.getToolingInterface(); // get the frame CallFrame myFrame = tools.getCallFrame( 0 ); // get local assertEquals( anInt, frame.getLocal( "anInt" ) ); 18
  • 28. Dynamic access to local variables public @Test void sampleOfAccessingLiveCallFrame() { int anInt = 4; // random number - by dice String aString = "some string value"; // get the tool ToolingInterface tools = ToolingInterface.getToolingInterface(); // get the frame CallFrame myFrame = tools.getCallFrame( 0 ); // get local assertEquals( anInt, frame.getLocal( "anInt" ) ); // update local anInt = 17; // most random number - proven! assertEquals( anInt, frame.getLocal( "anInt" ) ); 18
  • 29. Dynamic access to local variables public @Test void sampleOfAccessingLiveCallFrame() { int anInt = 4; // random number - by dice String aString = "some string value"; // get the tool ToolingInterface tools = ToolingInterface.getToolingInterface(); // get the frame CallFrame myFrame = tools.getCallFrame( 0 ); // get local assertEquals( anInt, frame.getLocal( "anInt" ) ); // update local anInt = 17; // most random number - proven! assertEquals( anInt, frame.getLocal( "anInt" ) ); // fancy get assertSame( aString ((CallFrame)myFrame.getLocal( "myFrame" )) .getLocal( "aString" ) ); 18
  • 30. Dynamic access to local variables public @Test void sampleOfAccessingLiveCallFrame() { int anInt = 4; // random number - by dice String aString = "some string value"; // get the tool ToolingInterface tools = ToolingInterface.getToolingInterface(); // get the frame CallFrame myFrame = tools.getCallFrame( 0 ); // get local assertEquals( anInt, frame.getLocal( "anInt" ) ); // update local anInt = 17; // most random number - proven! assertEquals( anInt, frame.getLocal( "anInt" ) ); // fancy get assertSame( aString ((CallFrame)myFrame.getLocal( "myFrame" )) .getLocal( "aString" ) ); // convenient this assertSame( this, frame.getThis() ); } 18
  • 31. code.samples(); 19 http://github.com/thobe/java-tooling
  • 32. JVMTI heap introspection 20
  • 33. Heap introspection ๏Native interface (JVMTI) ๏Abilities: •Following references •Tagging objects and classes •Getting tagged objects •Transitive reachability traversal •Iterating through all reachable objects •Iterating through all objects (reachable and not) •Iterating through all instances of a class •Getting object size •Getting object monitor usage 21
  • 34. code.sample(); 22 http://github.com/thobe/java-tooling
  • 35. Putting it all together: Live introspection 23
  • 36. code.demo(); 24 http://github.com/thobe/introscript
  • 37. Finding out more 25
  • 38. Web resources 26 ๏Java Debug Interface (JDI): http://docs.oracle.com/javase/7/docs/jdk/api/jpda/jdi/ ๏JVM Tooling Interface: http://docs.oracle.com/javase/7/docs/platform/jvmti/jvmti.html ๏JNI - JVMTI is an “extension” of JNI: http://docs.oracle.com/javase/7/docs/technotes/guides/jni/spec/jniTOC.html ๏Overview of JDK tools: http://docs.oracle.com/javase/7/docs/technotes/tools/index.html ๏JVM Attach API: http://docs.oracle.com/javase/7/docs/jdk/api/attach/spec/
  • 39. Code samples ๏http://github.com/thobe/java-tooling, contains: •Library for building tools in java ‣Soon: cross compiled native binaries for Mac OS X,Windows, Linux •Code examples showing how to use these tools ๏https://github.com/thobe/subprocess-testing, contains: •JDI-based JUnit TestRunner ๏http://github.com/thobe/java-agent, contains: •Java agent code injection ๏http://github.com/thobe/introscript, contains: •javax.script.ScriptEngine that attaches to other process and introspects it with above tools 27
  • 40. http://neotechnology.com