On HotSpot Error Files and Useful Tools - Mostly nerdless Learn all about HotSpot Error Files, a new syntax highlighter for VSCode and a redaction tool running directly in your browser.

Ever looked at a HotSpot error file and thought “nope”?
I wrote a guide + built a VSCode highlighter and a browser redaction tool (using @graalvm.org).
mostlynerdless.de/blog/2026/04...

🎓 JEP 534 moved to candidate
Title: Compact Object Headers by Default
Type: feature
Component: hotspot / runtime
See openjdk.org/jeps/534

youtu.be/7QWHRY07W2U
Hashmap perf, concurrent vs nonblocking, choosing your metric. Performance antipatterns (presentation), logging, cost of traces. Exceptions, error codes, stack traces in distributed system, deadlines,exceptions from other threads

Coffee Compiler Club, 2026_03_27 YouTube video by Cliff Click

youtu.be/20z1TDqST5k
Compiling regexs, Jury duty. LinkedIn talk - for Simple, loading code. Growing a Language. Operator overloading, for/while as functions, overload resolution, c++ templates, python, polymorphism. Back to H-M, implicit conversions, Immutable by default

Coffee Compiler Club, 2026_03_20 YouTube video by Cliff Click

youtu.be/c2uCdPzRy1w
Vibe coding, AI cheating, Simple philosophy, no commit, NBHM, C2/C++/Python perf, Faster C++ compiler. Interviews. PCs & DRAM prices. Graph viewers, Slow & broken build systems.

8364638: Refactor and make accumulated GC CPU time code generic by JonasNorlinder · Pull Request #26621 · openjdk/jdk Hi all, This PR refactors the newly added GC CPU time code from JDK-8359110. As a stepping-stone to enable consolidation of CPU time tracking in e.g. hsperf counters and GCTraceCPUTime and to have ...

github.com/openjdk/jdk/...

Java 26 quietly ships `-Xlog:cpu`, and it’s a perfect match with jbang. Run `jbang --java 26 -R=-Xlog:cpu <yourapp>` to see per-thread CPU stats without attaching a profiler. Handy way to sanity-check GC/VM activity.

✏️ JEP 8380294 was drafted
Title: Unbiased Stack-Walk API
Type: feature
Component: hotspot / jvmti
See openjdk.org/jeps/8380294

Java 26 / JDK 26: General Availability: mail.openjdk.org/archives/lis...

Features: openjdk.org/projects/jdk...

Downloads: jdk.java.net/26/

#Java26 #JDK26 #OpenJDK #Java

youtu.be/wTlwnDOQWvQ
Compiler driver as a graph; copy on write, modules, classes, lexing, EBNF, parser gens vs recursive decent; ambiguity; oper overload & oper parse; chained opers.
Compilers & Type theory, opts, DCE, eval, typescript vs tree shaking vs dyn class load.

✏️ JEP 8357464 was drafted
Title: Enhanced Local Variable Declarations (Preview)
Type: feature
Component: spec / lang
See openjdk.org/jeps/8357464

✏️ JEP 8379682 was drafted
Title: Make Shenandoah's generational mode the default
Type: feature
Component: hotspot / gc
See openjdk.org/jeps/8379682

youtu.be/PgcitUngWEk
Simple update, Graph debugger (qux, S-of-N), Storage types, tagged/untagged unions, Constexpr, partial eval, AST walking. Sea of Nodes eval vs Tier 0 JIT. NonBlockingHashMap design vs caches, hashCode, attack against

✏️ JEP 8344154 was drafted
Title: Convenience Methods for JSON Documents
Type: feature
Component: core / util
See openjdk.org/jeps/8344154

New blog: Testing the Datadog Explain Plan Visualizer with Oracle execution plans

tanelpoder.com/posts/testin...

youtu.be/E-M2Ccw3Kfw
Super light C++ stdlib. Keybindings & cross-OS muscle memory. AIs and their uses. Good CLI tools. VCS. Win 11 bashing. Levo editor story. Simple update - classless main execution, static.

✏️ JEP 8372760 was drafted
Title: JFR: In-Process Data Redaction
Type: feature
Component: hotspot / jfr
See openjdk.org/jeps/8372760

Redacting Sensitive Data from Java Flight Recorder Files - Mostly nerdless Redact sensitive data from Java Flight Recorder and JVM crash logs with jfr-redact, a tool for safely sharing profiling and error files.

Redact sensitive data from Java Flight Recorder and JVM crash logs with jfr-redact, a tool for safely sharing profiling and error files:

mostlynerdless.de/blog/2026/02...

youtu.be/I1cdM-K7WIw
Coffee Compiler Club - IR and type representations; ptr-pairs (type classes) vs embedded types ptr (java style). LLVM vs C2 object description. Type aliasing & compiler opts. Whole lotta state-of-the-AI conversation

Writing a .NET Garbage Collector in C#  - Part 7: Marking handles Using NativeAOT to write a .NET GC in C#. In the seventh part, we scan and update the handles during the mark phase of the garbage collection.

I published a new article in my "Writing a .NET GC in C#" series. This time, we implement a better storage for the handles, and we properly mark them during garbage collection. We also see why DependentHandles are annoying to deal with.

minidump.net/writing-a-ne...

10+ reasons to NOT use JDK’s HttpClient Java mostly, and general tech

Using the #JDK HttpClient, or … not.
Well it depends on each one’s use cases.

blog.arkey.fr/2026/02/08/t...

Coffee Compiler Club, 2026_01_16 YouTube video by Cliff Click

youtu.be/aN8-fn5sXME
Etherium interp, best? coding practices, getters, setters. Locking, old code in prod. Byzantine vs Paxos. unspec'd JSON, CSV. VMs, Cloud, Erlang, XTC, CPS, hierarchical timewheel. Interactive, gas,quotas. Concurrency, gradle. CI/CD, cbuild demo. comptime, metaprogramming

A free SQL explain plan visualizer tool by @datadoghq

Currently for PostgreSQL, MySQL, MSSQL and MongoDB

explain.datadoghq.com

✏️ JEP 8376595 was drafted
Title: Lazy Constants (Third Preview)
Type: feature
Component: core / lang
Release: 27
See openjdk.org/jeps/8376595

Writing a .NET Garbage Collector in C#  - Part 6: Mark and Sweep Using NativeAOT to write a .NET GC in C#. In the sixth part, we start implementing the mark phase of the garbage collection.

After a long wait, I've finally published the sixth part in my "Writing a .NET Garbage Collector in C#" series. Today, we start implementing mark and sweep.

minidump.net/writing-a-ne...

Coffee Compiler Club, 2026_01_16 YouTube video by Cliff Click

youtu.be/c1idAa4vV54
Concurrent hashmap, malloc vs GC vs thread-local, CAS, contention, atomics, arenas, pools. Capabilities, AI search vs grep. Channels vs mutex vs coroutines vs locks vs fork-join vs NBHM. Hotswap in HS, stack editing , unwinding, dynamic code loading

Updated JOL and heapdump-estimates in it specifically to better support JDK 25. We use this tool to quickly glance where are the opportunities in our real services. Streaming heap dump analysis allows doing this on multi-hundred GB heap dumps. Builds: builds.shipilev.net/jol/

Async-profiler has released an update that includes native lock profiling and a latency filter. Consequently, ap-loader, which wraps async-profiler in a platform-independent JAR, has also been updated: github.com/jvm-profilin...

Reading and Writing JFR Files Programmatically - Mostly nerdless JFR is great, but do you know how to read and write JFR files programmatically? Learn more in this week's blog post.

JFR is great, but do you know how to read and write JFR files programmatically? Learn more in this week's blog post: mostlynerdless.de/blog/2026/01...

How a 40-Line Fix Eliminated a 400x Performance Gap | QuestDB A deep dive into an OpenJDK commit that replaced slow /proc file parsing with a single syscall, revealing obscure Linux kernel internals and a 20-year-old optimization opportunity.

I did some OpenJDK commit exploration and I thought I could blog about it too. Here it is: questdb.com/blog/jvm-cur...