DSGL Hot Reload Agent

Native JVMTI agent for DSGL hot reload.

This subproject is written in Rust and built as a cdylib. It is loaded into the JVM and watches for class redefinition events. When that happens, it calls org.dreamfinity.dsgl.core.HotReloadBridge.markHotSwap(), so DSGL knows it needs to rebuild the UI.

This project is not part of the main Gradle multi-module build (:core, :adapters:mc-forge-1-7-10, :adapters:mc-forge-1-7-10:demo). It is built separately with Cargo.

Purpose

The agent does not perform hot swap itself and does not patch bytecode. Its job is only to detect that the JVM has redefined a class and notify DSGL.

On the DSGL side, DsglScreenHost checks HotReloadBridge.consumeHotSwap(). If the flag is set, it rebuilds the retained UI tree.

Relevant Files

• Agent: dsgl-hot-reload-agent/src/lib.rs
• Bridge flag: core/src/main/kotlin/org/dreamfinity/dsgl/core/HotReloadBridge.kt
• Rebuild trigger: adapters/mc-forge-1-7-10/src/main/kotlin/org/dreamfinity/dsgl/mcForge1710/DsglScreenHost.kt

How It Works

At startup, Agent_OnLoad acquires the JVMTI environment (JVMTI_VERSION_1_2) and enables the events the agent needs.

The agent listens to:

• VMInit
• ClassPrepare
• ClassFileLoadHook

When HotReloadBridge is prepared, the agent caches:

• a global reference to org/dreamfinity/dsgl/core/HotReloadBridge
• the static method ID for markHotSwap(): void

Later, when ClassFileLoadHook is invoked for a class redefinition (class_being_redefined != null), the agent calls the cached markHotSwap() method.

If the bridge has not been cached yet, the agent tries to resolve it again on the first redefine path.

Build

From repository root

cargo build --manifest-path dsgl-hot-reload-agent/Cargo.toml

The produced library name is OS-specific:

• Windows: dsgl_hot_reload_agent.dll
• Linux: libdsgl_hot_reload_agent.so
• macOS: libdsgl_hot_reload_agent.dylib