$ show alibaba/transmittable-thread-local
This repository provides TransmittableThreadLocal (TTL), a Java library that extends InheritableThreadLocal to propagate thread-local values across threads even when using thread pools, executors, ForkJoinPool, and other asynchronous constructs. It solves the common problem of context loss (e.g., tracing, security, session) in asynchronous Java applications. The library offers three usage modes: manual wrapping of Runnable/Callable via TtlRunnable/TtlCallable, wrapping executors via TtlExecutors, and transparent bytecode transformation via a Java Agent (TtlAgent) that automatically instruments JDK thread pool classes. The architecture is modular: ttl-core contains the core API and CRR (Capture-Replay-Restore) pattern, ttl-agent provides the agent with Javassist-based transformlets, ttl-kotlin adds Kotlin extensions, and ttl-integrations includes Vert.x 3/4 support. A ttl2-compatible module maintains backward compatibility with the v2 API. The library is widely adopted in the Java ecosystem (e.g., Apache ShardingSphere, SOFARPC) and is under active development with a v3 branch introducing a refined API. While primarily a library, it includes a Java Agent component that operates at the JVM level, making it a hybrid of library and instrumentation tool.
The LLM identified 4 files worth highlighting for reuse:
Implements the Composite pattern over multiple Transmittable sources, allowing capture, replay, and restore of thread-local context from multiple origins (e.g., TransmittableThreadLocal and registered ThreadLocal instances). This is a clean, reusable implementation of the CRR pattern that could be extracted for any context propagation framework.
Defines a generic wrapper interface with a getWrappedObject() method, enabling uniform unwrapping of TTL-enhanced objects (e.g., TtlRunnable, TtlCallable, wrapped executors). This SPI is used throughout the library and can be reused in any project needing a standardized wrapper/unwrapper pattern.
Provides a base class for creating Java Agent transformlets that instrument executor classes. It handles common logic like checking if the agent is loaded, applying transformations to execute methods, and integrating with the TTL framework. This is a reusable template for building custom agent extensions for other thread pool implementations.
Contains utility methods for bytecode manipulation using Javassist, such as inserting code before/after method calls, checking method signatures, and handling class loading. This helper is used by all built-in transformlets and can be reused in any Javassist-based agent project.