Download Multiple simultaneous agents

New debug/profile features in J2SE 6
Ivan Popov, May, 2006
Intel Corporation
1
Title
New features in J2SE 6 (JSR-270, core/debug)
 Access to heap contents (JDI, JDWP)
 rewritten JVMTI functions and callbacks for heap iteration
 new JDI and JDWP functions for finding objects in heap
 Attach-on-demand (JVMTI, java.lang.instrument)
 new entry points for dynamically loaded JVMTI and Java agents
 no spec for dynamic loading mechanism (implementation dependent)
 Multiple simultaneous agents (JVMTI, java.lang.instrument)
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
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defined algorithm of sequential classfile transformation
introduced transformation capable/incapable agents
new function RetransformClasses() in addition to RedefineClasses()
support for instrumenting native calls by providing Java wrappers
 Several other changes in JVMTI, JDI, JDWP
 Getting monitor info for stack frames, access to constant pool, etc.
 JVMDI and JVMPI are removed
2
Title
Access to heap content
 JVMTI
 new set of heap iteration functions and callbacks
 similar functionality but new design
 old functions are still in JVMTI spec (marked version 1.0)
 JDI/JDWP
 Get all objects of a given class
 Get all objects which refer to a given object
3
Title
Attach-on-demand
 JVMTI:
 new entry point for dynamically loaded JVMTI agents
 Agent_OnAttach() vs. Agent_OnLoad()
 java.lang.instrument:
 new entry point for dynamically loaded Java agents
 agentmain() vs. premain()
 Problems:
 no spec for algorithm of dynamic agent loading – it is implementation
specific
 no particular support for detach-on-demand
4
Title
Multiple simultaneous agents
(bytecode instrumentation)
 JVMTI:
 described support for multiple classfile transformations
 introduced classfile retransformation algorithm for new transformation
capable agents
 supports classfile redefinition algorithm for old transformation incapable
agents
 clarified semantics of RedefineClasses(), RetransformClasses(),
CLASS_FILE_LOAD_HOOK for agents of both kinds
 the whole algorithm is quite sophisticated
 java.lang.instrument:
 similar features for Java agents
5
Title
New features in J2SE 6 (JSR-270, core/debug)
 Access to heap contents (JDI, JDWP)
 rewritten JVMTI functions and callbacks for heap iteration
 new JDI and JDWP functions for finding objects in heap
 Attach-on-demand (JVMTI, java.lang.instrument)
 new entry points for dynamically loaded JVMTI and Java agents
 no spec for dynamic loading mechanism (implementation dependent)
 Multiple simultaneous agents (JVMTI, java.lang.instrument)




defined algorithm of sequential classfile transformation
introduced transformation capable/incapable agents
new function RetransformClasses() in addition to RedefineClasses()
support for instrumenting native calls by providing Java wrappers
 Several other changes in JVMTI, JDI, JDWP
 Getting monitor info for stack frames, access to constant pool, etc.
 JVMDI and JVMPI are removed
6
Title
Instrumenting native calls
 JVMTI:
 replacing native methods with Java wrappers
 adding prefixes for renaming original native methods
 managing prefixes for single and multiple agents
 clarified algorithm for binding native methods using prefixes
 the overall algorithm is quite sophisticated
7
Title
Other spec changes
 JVMTI, JDWP, JDI:
 Get locked monitors for frames
 new functions return association between frames and locked monitors
 support for monitor events on JDI/JDWP level
 Access to constant pool
 get classfile major/minor version
 get constant pool bytes
 Checking unmodifiable classes
 new function checks if class bytecode can be modified
 Force early method return
 new function to force method to return with given value
 new METHOD_EXIT_WITH_RETURN_VALUE event in JDI/JDWP
8
Title
Other spec changes (cont.)
 JVMTI:
 modification of class path for both bootstrap and system loaders:
 AddToSystemClassLoaderSearch vs.
AddToBootstrapClassLoaderSearch
 JDI/JDWP:
 source file filter for CLASS_PREPARE events
 new JDI connector ProcessAttach uses PID for attaching to process
 eliminates knowing port number for attaching connection
 transport is determined dynamically and reported as “local”
 no details of the algorithm
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Title