How does code hot swapping work, and what are its pitfalls?

on YouTube ↗14m

" summary

Demo shows a tiny running program with an embedded webserver, decompiler and an Update button that compiles code and pushes classes into the JVM. Hot swap uses JVMTI-like hooks or the java.lang.instrumentation agent calling redefineClasses or retransform to replace bytecode; common generators are javac/compiler API, ASM or ByteBuddy. Works for turning tracing on or capturing locals but cannot add or remove fields or methods or change signatures or inheritance, and repeated swaps cause deoptimization, safepoint pauses and metaspace growth after hundreds or thousands.

AI-written summary · about

" chapters (7)

1. 0:00Code hot swapping intro
2. 2:31Hot swapping in Java
3. 5:43JVM TI and Java agents
4. 9:35Generating bytecode
5. 10:39Hot swap use cases
6. 11:42Hot swap pitfalls
7. 13:11Q&A

" related talks

• 46mThe Hitchhiker’s guide to Java class reloadingAnton Arhipov · Voxxed Days Bucharest 2018
• 55mMaking Java more dynamicRafael Winterhalter · Jfokus 2016
• 49mAn Introduction to JVM PerformanceRafael Winterhalter · Devoxx Belgium 2017
• 59mAn Introduction to JVM PerformanceRafael Winterhalter · JavaDay Lviv 2016
• 01h 09mFrom Bytecode to Native Code in HotSpot JVMIonut Balosin · Voxxed Days Bucharest 2016
• 41mAn Introduction to JVM PerformanceRafael Winterhalter · GOTO Oslo 2020
• 01h 01mAn Introduction to JVM PerformanceRafael Winterhalter · JavaOne 2015
• 45mMaking Java more dynamicRafael Winterhalter · JavaDay Lviv 2016