JVMTI#

JVMTI 相关数据结构#

说到 JNI，对于 Java 观察工具及其实现有兴趣的同学，不得不提一下基于 JNI 基础架构上的 JVMTI。

What is the JVM Tool Interface?#

The JVMTM Tool Interface (JVM TI) is a programming interface used by development and monitoring tools. It provides both a way to inspect the state and to control the execution of applications running in the JavaTM virtual machine (VM).

JVM TI is intended to provide a VM interface for the full breadth of tools that need access to VM state, including but not limited to: profiling, debugging, monitoring, thread analysis, and coverage analysis tools.

JVM TI may not be available in all implementations of the JavaTM virtual machine.

JVM TI is a two-way interface:

A client of JVM TI, hereafter called an agent,
can be notified of interesting occurrences through events.

JVM TI can query and control the application through many functions, either in response to events or independent of them.

Agents run in the same process with and communicate directly with the virtual machine executing the application being examined. This communication is through a native interface (JVM TI). The native in-process interface allows maximal control with minimal intrusion on the part of a tool. Typically, agents are relatively compact. They can be controlled by a separate process which implements the bulk of a tool’s function without interfering with the target application’s normal execution.

Architecture#

Tools can be written directly to JVM TI or indirectly through higher level interfaces. The Java Platform Debugger Architecture includes JVM TI, but also contains higher-level, out-of-process debugger interfaces. The higher-level interfaces are more appropriate than JVM TI for many tools. For more information on the Java Platform Debugger Architecture, see the Java Platform Debugger Architecture website.

JVM TI 实现#

以下部分内容源自 JVM Tool Interface(JVM TI) Implementation in HotSpot(2007) - Robert.Field@Sun.com 以下简称为 JVM TI Impl - ReobertField

JVM TI 实现内部使用分层设计，由高层到底层分别为：

User agent
- JVM TI
JVM TI View 层
- jvmtiEnv.hpp
JVM TI 实现层
- jvmtiExport.hpp
VM Core

分层实现 - JVM TI View 层#

生成的 interface 和辅助转接代码(transition code)

jvmti.h : JVM TI 规范标准的 interface – C语言 interface)
- 位于 hotspot/variant-server/gensrc/jvmtifiles/jvmti.h
jvmtiEnv.hpp : HotSpot JVM TI C++语言 interface
- 位于 hotspot/variant-server/gensrc/jvmtifiles/jvmtiEnv.hpp
jvmtiEnter.cpp : 辅助转接代码(transition code)
- 位于 hotspot/variant-server/gensrc/jvmtifiles/jvmtiEnv.hpp