A December tech tip article explains some basics of writing a JavaTM Virtual Machine (JVMTM) tool interface (JVM TI) agent library by walking through the heapTracker demo agent available in the JDK downloads. Senior staff engineer Kelly O-Hair and writer Janice Heiss provide code samples as well in "The JVM Tool Interface (JVM TI): How VM Agents Work".

Tips include being cautious about how much memory to allocate. Too much will cause the VM process to fail. Also, make sure the process can locate the library.

A DVM agent is not needed because the JDK 6 release includes "virtually all the required built-in DTrace probes", according to the authors.

A code sample (abbreviated) shows what agent initialization looks like.

Also in the tech tip are:

• Event Callbacks, code for cbClassFileLoadHook

• How to set up the Tracker class for the VM start event

• The importance of knowing what the stack trace is and to tag the object with a reference to that information

• Make sure all the event callbacks are completed

See the full article in SDN.

(Please note the terms "Java Virtual Machine" and "JVM" mean a Virtual Machine for the Java platform.) [...read more...]

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