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JavaOne 2017 - The hitchhiker’s guide to Java class reloading
The document discusses Java class reloading, emphasizing the time lost during container startup and application deployment. It explores technical solutions such as hotswap, class loaders, and JVM features, along with insights from past works on dynamic code evolution. The content also highlights the challenges and complexities associated with implementing these techniques effectively.
JavaOne 2017 - The hitchhiker’s guide to Java class reloading
- 1. The hitchhiker’s guideto Java class reloading @antonarhipov
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- 6. https://zeroturnaround.com/rebellabs/java-ee-productivity-report-2011/ 10% 20% 30% 0.5 1 23 4 5 6 7 8 10+ minutes
- 7. https://zeroturnaround.com/rebellabs/java-ee-productivity-report-2011/ 10% 20% 30% 0.5 1 23 4 5 6 7 8 10+ The only effective developers?? minutes
- 8. https://zeroturnaround.com/rebellabs/java-ee-productivity-report-2011/ 10% 20% 30% 0.5 1 23 4 5 6 7 8 10+ How about those? minutes
- 9. The problem: where didthe time go?
- 10. The problem: where didthe time go? 1-30 sec Container startup time
- 11. The problem: where didthe time go? 1-30 sec Container startup time ~3 min 30 min1 s Application deployment
- 12. The problem: where didthe time go? 1-30 sec Container startup time ~3 min 30 min1 s Application deployment ~1 min Navigation
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- 16. Technical solutions HotSwap Class loaders Javaagents & instrumentation
- 17. Technical solutions HotSwap Class loaders Javaagents & instrumentation
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- 33. instanceKlass constantPoolOop constants() pool_holder() klassVTable Embedded klassITable Embedded Embedded statics M. Dmitriev.Safe class and data evolution in large and long-lived Java (тм) applications. Technical report, Mountain View. 2001
- 34. instanceKlass constantPoolOop constants() constantPoolCacheOop cache() pool_holder() klassVTable Embedded klassITable Embedded Embedded statics M. Dmitriev.Safe class and data evolution in large and long-lived Java (тм) applications. Technical report, Mountain View. 2001
- 35. instanceKlass constantPoolOop constants() constantPoolCacheOop cache() pool_holder() klassVTable Embedded klassITable Embedded Embedded statics objArrayOop methodOop methods() M. Dmitriev.Safe class and data evolution in large and long-lived Java (тм) applications. Technical report, Mountain View. 2001
- 36. instanceKlass constantPoolOop constants() constantPoolCacheOop cache() pool_holder() klassVTable Embedded klassITable Embedded Embedded statics nmethod code() method() constants() objArrayOop methodOop methods() M. Dmitriev.Safe class and data evolution in large and long-lived Java (тм) applications. Technical report, Mountain View. 2001
- 37. instanceKlass constantPoolOop constants() constantPoolCacheOop cache() pool_holder() klassVTable Embedded klassITable Embedded Embedded statics nmethod code() method() constants() objArrayOop methodOop methods() M. Dmitriev.Safe class and data evolution in large and long-lived Java (тм) applications. Technical report, Mountain View. 2001 Limited to individual statements
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- 39. Dynamic Code Evolutionfor Java T. Würthinger, C. Wimmer, L. Stadler. 2010
- 40. Dynamic Code Evolutionfor Java T. Würthinger, C. Wimmer, L. Stadler. 2010 Statements
- 41. Dynamic Code Evolutionfor Java T. Würthinger, C. Wimmer, L. Stadler. 2010 Statements Methods
- 42. Dynamic Code Evolutionfor Java T. Würthinger, C. Wimmer, L. Stadler. 2010 Statements Methods Fields
- 43. Dynamic Code Evolutionfor Java T. Würthinger, C. Wimmer, L. Stadler. 2010 Statements Methods Fields Hierarchy
- 44. Dynamic Code Evolutionfor Java T. Würthinger, C. Wimmer, L. Stadler. 2010 Statements Methods Fields Hierarchy
- 45. Dynamic Code Evolutionfor Java T. Würthinger, C. Wimmer, L. Stadler. 2010 Statements Methods Fields Hierarchy + + + Binary-compatible
- 46. Dynamic Code Evolutionfor Java T. Würthinger, C. Wimmer, L. Stadler. 2010 Statements Methods Fields Hierarchy + + + x x x Binary-compatible Binary-incompatible
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- 49. Class<?> uc1 =User.class; Class<?> uc2 = new DynamicClassLoader().load("com.zt.User"); out.println(uc1.getName()); // com.zt.User out.println(uc2.getName()); // com.zt.User out.println(uc1.getClassLoader()); // sun.misc.Launcher$AppClassLoader@18b4aac2 out.println(uc2.getClassLoader()); // com.zt.DynamicClassLoader@22b4bba7 User.age = 11; out.println((int) ReflectUtil.getStaticFieldValue("age", uc1)); // 11 out.println((int) ReflectUtil.getStaticFieldValue("age", uc2)); // 10 public class User { public static int age = 10; }
- 50. Class<?> uc1 =User.class; Class<?> uc2 = new DynamicClassLoader().load("com.zt.User"); out.println(uc1.getName()); // com.zt.User out.println(uc2.getName()); // com.zt.User out.println(uc1.getClassLoader()); // sun.misc.Launcher$AppClassLoader@18b4aac2 out.println(uc2.getClassLoader()); // com.zt.DynamicClassLoader@22b4bba7 User.age = 11; out.println((int) ReflectUtil.getStaticFieldValue("age", uc1)); // 11 out.println((int) ReflectUtil.getStaticFieldValue("age", uc2)); // 10 public class User { public static int age = 10; }
- 51. Class<?> uc1 =User.class; Class<?> uc2 = new DynamicClassLoader().load("com.zt.User"); out.println(uc1.getName()); // com.zt.User out.println(uc2.getName()); // com.zt.User out.println(uc1.getClassLoader()); // sun.misc.Launcher$AppClassLoader@18b4aac2 out.println(uc2.getClassLoader()); // com.zt.DynamicClassLoader@22b4bba7 User.age = 11; out.println((int) ReflectUtil.getStaticFieldValue("age", uc1)); // 11 out.println((int) ReflectUtil.getStaticFieldValue("age", uc2)); // 10 public class User { public static int age = 10; }
- 52. Class<?> uc1 =User.class; Class<?> uc2 = new DynamicClassLoader().load("com.zt.User"); out.println(uc1.getName()); // com.zt.User out.println(uc2.getName()); // com.zt.User out.println(uc1.getClassLoader()); // sun.misc.Launcher$AppClassLoader@18b4aac2 out.println(uc2.getClassLoader()); // com.zt.DynamicClassLoader@22b4bba7 User.age = 11; out.println((int) ReflectUtil.getStaticFieldValue("age", uc1)); // 11 out.println((int) ReflectUtil.getStaticFieldValue("age", uc2)); // 10 public class User { public static int age = 10; }
- 53. Class<?> uc1 =User.class; Class<?> uc2 = new DynamicClassLoader().load("com.zt.User"); out.println(uc1.getName()); // com.zt.User out.println(uc2.getName()); // com.zt.User out.println(uc1.getClassLoader()); // sun.misc.Launcher$AppClassLoader@18b4aac2 out.println(uc2.getClassLoader()); // com.zt.DynamicClassLoader@22b4bba7 User.age = 11; out.println((int) ReflectUtil.getStaticFieldValue("age", uc1)); // 11 out.println((int) ReflectUtil.getStaticFieldValue("age", uc2)); // 10 public class User { public static int age = 10; }
- 54. while(true) { Class<?> uc= new DynamicClassLoader().load("com.zt.User"); ReflectUtil.invokeStatic("getHobby", uc); } public class User { public Hobby getHobby() { return Basketball(); } }
- 55. while(true) { Class<?> uc= new DynamicClassLoader().load("com.zt.User"); ReflectUtil.invokeStatic("getHobby", uc); } public class User { public Hobby getHobby() { return Basketball(); } }
- 56. while(true) { Class<?> uc= new DynamicClassLoader().load("com.zt.User"); ReflectUtil.invokeStatic("getHobby", uc); } public class User { public Hobby getHobby() { return Basketball(); } } Assume there is a trigger / event
- 57. public static classContext { public HobbyService hobbyService = new HobbyService(); public void init() { hobbyService.user = new User(); anyService.initialize() } }
- 58. public static classContext { public HobbyService hobbyService = new HobbyService(); public AnyService anyService = new AnyService(); public void init() { hobbyService.user = new User(); anyService.initialize() } }
- 59. public static classContext { public HobbyService hobbyService = new HobbyService(); public AnyService anyService = new AnyService(); public void init() { hobbyService.user = new User(); anyService.initialize() } } while(true) { Class<?> c = new DynamicClassLoader().load("com.zt.Context"); Object context = c.newInstance(); ReflectUtil.invokeMethod("init", context); invokeService(context); }
- 60. DynamicClassLoader Context class HobbyService class Userclass Context object HobbyService object User object Reloadable “region” Live thread
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- 68. import java.lang.instrument.ClassFileTransformer; import java.lang.instrument.Instrumentation; publicclass Agent { public static void premain(String args, Instrumentation inst) throws Exception { inst.addTransformer(new ClassFileTransformer { // here be dragons }); } }
- 69. import java.lang.instrument.ClassFileTransformer; import java.lang.instrument.Instrumentation; publicclass Agent { public static void premain(String args, Instrumentation inst) throws Exception { inst.addTransformer(new ClassFileTransformer { // here be dragons }); } } META-INF/MANIFEST.MF Premain-Class: Agent
- 70. import java.lang.instrument.ClassFileTransformer; import java.lang.instrument.Instrumentation; publicclass Agent { public static void premain(String args, Instrumentation inst) throws Exception { inst.addTransformer(new ClassFileTransformer { // here be dragons }); } } $> java –javaagent:agent.jar application.Main META-INF/MANIFEST.MF Premain-Class: Agent
- 71. ClassFileTransformer ClassA ClassA ClassA0 +field1 +field2 +field3 +method1 +method2 +method3 +method1 +method2 +method3 +field1 +field2 +field3 +proxy_methods A thousand yearsof productivity: the JRebel story E. Kabanov, V. Vene, 2012
- 72. ClassFileTransformer ClassA ClassA ClassA0 +field1 +field2 +field3 +method1 +method2 +method3 +method1 +method2 +method3 +field1 +field2 +field3 +proxy_methods A thousand yearsof productivity: the JRebel story E. Kabanov, V. Vene, 2012
- 74. What did welearn today?
- 75. What did welearn today? HotSwap - a feature of your JVM, not IDE!
- 76. What did welearn today? HotSwap - a feature of your JVM, not IDE! Class loaders - easy to implement, but limited
- 77. What did welearn today? HotSwap - a feature of your JVM, not IDE! Class loaders - easy to implement, but limited Java agents & instrumentation - very tricky!
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