Enhancements in JDK 6
JavaTM Virtual Machine Tool
Interface (JVM TI)
The following functionality has been added to the
JVMTM tool interface (JVM TI)
between its initial release in JDK 5.0 and JDK 6.
- Support for transformation of class files - To
facilitate dynamic transformation of classes which have already
been loaded, the
RetransformClasses
function has been added. It is suited to operations such as adding
instrumentation to methods. Support for retransformation means that
access to the original class file is no longer required in order to
instrument loaded classes. It can easily remove the applied
transformation and it is designed to work in a multi-agent
environment.
- Enhanced heap walking support - More powerful and
flexible heap
functionality has been added. The new functionality:
- allows access to primitive values (the value of Strings,
arrays, and primitive fields)
- allows the tag of the referrer to be set, thus enabling more
efficient localized reference graph building
- provides more extensive filtering abilities
- is extensible, allowing abilities to grow in future versions of
JVM TI
The FollowReferences
and IterateThroughHeap
functions have been added along with supporting types and
constants. The previous functionality is still supported but its
use is discouraged.
- More class information - The new
GetConstantPool,
GetClassVersionNumbers
and IsModifiableClass
functions provide additional information about a class.
- Support for instrumenting native methods - The new
SetNativeMethodPrefix
and SetNativeMethodPrefixes
functions allow native methods to be instrumented by providing a
JVM-aware mechanism for wrapping the native method.
- Enhanced support for instrumentation under the system class
loader - The new
AddToSystemClassLoaderSearch function allows
instrumentation support classes to be defined by the system class
loader.
- Support for early return from a method - The new
force
early return functions allow debugger-like tools to force a
method to return from any point in its execution.
- Monitor stack depth information - The new
GetOwnedMonitorStackDepthInfo function provides
information about the monitors owned by the specified thread and
the depth of the stack frame which locked them.
- Support for resource exhaustion notification - The new
ResourceExhausted
event notifies the JVM when a critical resource (such as the
JavaTM platform heap) has been
exhausted.
Other changes between JDK 5.0 and JDK 6 include new error codes, a
revised definition for field index, allowing
AddToBootstrapClassLoaderSearch to be called in
the live phase, and considerable specification clean-up and
clarification. For detailed information about the changes, see the
Change
History.
