JVMTI

JVMTI, or the Java Virtual Machine Tool Interface, is a native programming interface that enables tools to inspect, monitor, profile, and control the execution of applications running on the Java Virtual Machine. It is designed to be used by performance profilers, debuggers, and monitoring tools to gather information about the running JVM and modify its behavior when necessary.

JVMTI is part of the Java Platform Debugger Architecture (JPDA) and is implemented by compatible JVMs such as HotSpot. Tools that use JVMTI are implemented as native agents written in C or C++, loaded into the JVM at startup or attached to a running process via a dynamic library. Once loaded, the agent obtains a jvmtiEnv interface through which it can call a wide range of functions to observe and influence the VM.

The interface provides a capability mechanism to enable particular features and an event notification system to report significant moments during execution. Common events include VM initialization and death, thread start and end, class preparation, method entry and exit, field access and modification, exceptions, and class file loading or retransformation. Through these facilities, agents can examine thread states and call stacks, inspect and modify local variables, retrieve object information, define or redefine classes, and perform bytecode instrumentation.

Typical uses of JVMTI include creating profilers, debuggers, and runtime instrumentation tools. It is widely employed by commercial and open-source products such as performance profilers and monitoring suites and is compatible with multiple JVM implementations that support the JVMTI standard. Access to JVMTI requires appropriate permissions and is restricted to the JVM process in which the agent runs.