MethodEntryEvent

MethodEntryEvent is a runtime event used by profiling, tracing, and debugging infrastructures to signal the moment execution enters a specific method. It is triggered when a thread begins executing the first instruction of a method, typically just after control transfers from the caller. The event enables observers to collect timing, invocation, and control-flow data as code runs.

A MethodEntryEvent usually carries metadata that identifies the target method and context. Common fields include the method’s fully qualified name, the declaring class or type, the method signature or descriptor, and whether the method is static or instance. Additional context may be provided, such as the thread on which the method is entered, a timestamp, the current call depth, and, for non-static methods, a reference to the this-object or receiver. Depending on the framework, more details like the caller method, application module, or instrumentation point may also be included.

Usage of MethodEntryEvent centers on collecting and analyzing runtime behavior. Observers can count invocations, measure execution time, track call graphs, or implement coverage and debugging features. Events may be processed by native agents, managed profilers, or external tracing systems, often with options to filter by method, class, or thread to reduce overhead. In many environments, the event representation is optimized to be lightweight, with richer payloads available only when instrumentation is enabled.

In different ecosystems, the event may be exposed under different names but serves the same concept. For example, JVMTI provides a method-entry event for native agents, while similar functionality exists under function-entry events in other profiling APIs. MethodEntryEvent thus denotes the standardized moment of entering a method used across instrumentation ecosystems.