1. Eclipse TPTP TPTP Heap and Thread Profilers High-level Design Rev 1.0 Asaf Yaffe July, 2006

2. Eclipse TPTP Heap Profiler

3. Eclipse TPTP Profiler Requirements Track object allocations and de-allocations Track GC events Produce heap dumps on demand Generate XML trace compatible with the JVMPI Heap Profiler

4. Eclipse TPTP Martini Requirements Generate the following events –Object Alloc –Object Free –GC Start –GC Finish Support the following data requests –Get Object information (from an object id) –Get Class information (from a class id) –Get Reference graph for living objects (heap dump)

5. Eclipse TPTP Martini Heap Events Overview Martini uses intra-function instrumentation for generating Object Alloc events For all reference types except arrays, the Object Alloc event is generated by instrumenting the constructor of the java.lang.Object class –The instrumentation code passes the newly allocated object reference to a Java static recorder function HeapProxy.ObjectAlloc which calls back into JPIHeapProxy –JPI tags the allocated object (via JVMTI) in order for the JVM to identify the object in the Object Free event communicated by the JVM via JVMTI –This technique is sub-optimal but easy to implement Selectivity is implemented on Object Alloc event rather than during instrumentation May be optimized in future slices For array types, the Object Alloc event is generated by instrumenting array allocation sites (i.e., after newarray, anewarray, multianewarray) The instrumentation activity takes place during CLASS_LOAD_HOOK event of the java.lang.Object class or when heap events are dynamically enabled by the tool

6. Eclipse TPTP The HeapProxy Class Martini has a helper HeapProxy Java classHeapProxy –Resides in a directory that is added to the JVM boot CLASSPATH during JPI initialization The Problem: the HeapProxy recorder methods are defined as native and are bound by JPI only during the JVM_INIT event (because JNI services are not available before JVM_INIT) –This is problematic since for some system classes, CLASS_LOAD_HOOK events are sent before JVM_INIT –Inserting calls to native methods before they are bound cause the JVM to crash, even if these methods are never executed (just referencing these methods in the code is enough to crash the JVM) The Solution: HeapProxy has wrapper functions which are always called by instrumentation code that is inserted before JVM_INIT –Those functions check whether the JVM has already been initialized and call the native ObjectAlloc functions only after the JVM has been initialized i.e. object allocations before JVM_INIT after not communicated to the heap profiler

7. Eclipse TPTP Object Alloc Event Event Source –Regular Objects: BCI of java.lang.Object. –Arrays: BCI after callsites of newarray, anewarray, multianewarray –Internal VM Allocations: JVMTI_EVENT_VM_OBJECT_ALLOC Data Items –Object ID –Class ID –Thread id (of the allocating thread) –Object Size –Whether this object is an array Selectivity –By package/class

8. Eclipse TPTP Object Free Event Event Source –JVMTI_EVENT_OBJECT_FREE for tagged objects Data Items –Object ID (easy - JVMTI) –All other information is optional Can also be looked-up using a data request Selectivity –By fully qualified class name –Defined at Object Allocation time for both Object Alloc and Free events

9. Eclipse TPTP Garbage Collection Started Event Source –JVMTI_EVENT_GARBAGE_COLLECTION_START Data Items –None Selectivity –None Notes –Generated only for stop-the-world collections. Other collections are not reported.

10. Eclipse TPTP Garbage Collection Finished Event Source –JVMTI_EVENT_GARBAGE_COLLECTION_FINISH Data Items –None Selectivity –None Notes –See Garbage Collection Started

11. Eclipse TPTP Heap Dump/Object References TBD…

12. Eclipse TPTP Open Issues Heap Dump data –Need more info about the following XML fragments and their attributes: heapDumpDef gcRoot objectReference gcFinish element –Are the following attributes used by the viewers: usedObjects, usedObjSpace, totalObjSpace

13. Eclipse TPTP Thread Profiler

14. Eclipse TPTP Profiler Requirements Track Thread start and end events Track monitor events (critical sections, wait) Generate XML trace compatible with the JVMPI implementation

15. Eclipse TPTP Martini Requirements Generate the following events –Thread Start –Thread End –Contended Monitor Enter –Contended Monitor Entered –Monitor Wait –Monitor Waited Support the following data requests –Get Object Monitor Usage information (from an object id) –Get Thread information (from a thread id)

16. Eclipse TPTP Thread Start Event Event Source –JVMTI Data Items –Unique Thread ID –Thread Name –Parent Name –Group Name Selectivity –None

17. Eclipse TPTP Thread End Event Event Source –JVMTI Data Items –Thread ID Selectivity –None

18. Eclipse TPTP Contended Monitor Enter Event Event Source –JVMTI Data Items –Unique Monitor ID –The waiting thread id –The id of the thread owning the monitor Notes –Other monitor information can be obtained with a data request: For contended monitors: a list of threads waiting for the monitor For wait monitors: a list of threads waiting to be notified

19. Eclipse TPTP Contended Monitor Entered Event Event Source –JVMTI Data Items –Monitor ID –The id of the thread that entered the monitor Selectivity –None

20. Eclipse TPTP Monitor Wait Event Event Source –JVMTI Data Items –Monitor ID –The id of the waiting thread –Wait timeout - the value passed to the obj.Wait() method Selectivity –None

21. Eclipse TPTP Monitor Waited Event Event Source –JVMTI Data Items –Monitor ID –The id of the waiting thread Selectivity –None Notes –The output element includes the timeout attribute that specifies the number of milliseconds the thread had to wait for the monitor. –This data item is not available in JVMTI so the profiler will have to calculate it manually

22. Eclipse TPTP Backup

23. Eclipse TPTP HeapProxy Java Class public class HeapProxy { private static int m_bJVMInit = 0; public static void JVMInit() { m_bJVMInit = 1; } public static native void ObjectAlloc(java.lang.Object obj); public static void EarlyObjectAlloc(java.lang.Object obj) { if (m_bJVMInit != 0) ObjectAlloc(obj); } public static native void ArrayAlloc(java.lang.Object arr); public static void EarlyArrayAlloc(java.lang.Object arr) { if (m_bJVMInit != 0) ArrayAlloc(obj); }

24. Eclipse TPTP Instrumenting java.lang.Object Constructor BeforeAfter public Object() { } public Object() { HeapProxy.EarlyObjectAlloc(this); } Best seen in Slide Show mode Martini inserts a call to HeapProxy.EarlyObjectAlloc, because the insertion will always happen before the VM is initialized, and we cannot use native methods because they were not bound yet.

25. Eclipse TPTP Instrumenting Array Allocation Callsites [case 1 – before JVM_INIT event received] Before After void someMethod() { … int[] intArray = new int[20]; … } Best seen in Slide Show mode void someMethod() { … int[] intArray = new int[20]; HeapProxy.EarlyArrayAlloc(intArray); … } Martini inserts a call to HeapProxy.EarlyArrayAlloc. Since the JVM has not been initialized yet, we cannot use native methods because they were not bound yet.

26. Eclipse TPTP Instrumenting Array Allocation Callsites [case 2 – after JVM_INIT event received] Before After void someMethod() { … int[] intArray = new int[20]; … } Best seen in Slide Show mode void someMethod() { … int[] intArray = new int[20]; HeapProxy.ArrayAlloc(intArray); … } Martini inserts a call to HeapProxy.ArrayAlloc. Since the JVM has already initialized, we can safely use native methods because they were already bounded.

27. Eclipse TPTP Heap Instrumentation Overview Instrumenting the java.lang.Object constructor: –Add references to the HeapProxy class and the HeapProxy.EarlyObjectAlloc function to the constant pool –Modify the methods code attribute and inject code to call the HeapProxy.EarlyObjectAlloc function. Instrumenting array allocation sites in a Java class: –Add references to the HeapProxy class and the HeapProxy.ArrayAlloc or HeapProxy.EarlyObjectAlloc functions to the constant pool –Iterate over the class methods, and for each method that can be instrumented (i.e. has a code attribute) Search for any of the following array allocation instructions: newarray, anewarray, multianewarray. If found, modify the methods code attribute and inject code after each allocation site to call the HeapProxy.ArrayAlloc function.

28. Eclipse TPTP java.lang.Object Constructor Instrumentation Details return.end.start Original method code Legend pseudo-instructions original instructions new instructions.start inst1 sipush Instrumented method code.start aload_0 invokestatic EarlyObjectAlloc().end return Best seen in Slide Show mode The this pointer of the newly allocated object is stored in local variable 0. Load it to the operand stack so it can be passed to the EarlyObjectAlloc static function

29. Eclipse TPTP Array Allocation Site Instrumentation Details.end.start Original method code Legend pseudo-instructions original instructions new instructions.start inst1 sipush Instrumented method code.start dup invokestatic [Early]ArrayAlloc().end inst Best seen in Slide Show mode newarray inst newarray inst After the newarray instruction, a reference to the newly allocated array is on the operand stack. The reference is duplicated and sent to the ArrayAlloc or EarlyArrayAlloc static function