Bruno Deferrari tizoc

Quick Tips for Fast Code on the JVM

I was talking to a coworker recently about general techniques that almost always form the core of any effort to write very fast, down-to-the-metal hot path code on the JVM, and they pointed out that there really isn't a particularly good place to go for this information. It occurred to me that, really, I had more or less picked up all of it by word of mouth and experience, and there just aren't any good reference sources on the topic. So… here's my word of mouth.

This is by no means a comprehensive gist. It's also important to understand that the techniques that I outline in here are not 100% absolute either. Performance on the JVM is an incredibly complicated subject, and while there are rules that almost always hold true, the "almost" remains very salient. Also, for many or even most applications, there will be other techniques that I'm not mentioning which will have a greater impact. JMH, Java Flight Recorder, and a good profiler are your very best friend! Mea

Falsehoods programmers believe about time

This is a compiled list of falsehoods programmers tend to believe about working with time.

Don't re-invent a date time library yourself. If you think you understand everything about time, you're probably doing it wrong.

Falsehoods

There are always 24 hours in a day.
February is always 28 days long.
Any 24-hour period will always begin and end in the same day (or week, or month).

Methods of Signing Git Commits on MacOS

Last updated March 13, 2024

This Gist explains how to sign commits using gpg in a step-by-step fashion. Previously, krypt.co was heavily mentioned, but I've only recently learned they were acquired by Akamai and no longer update their previous free products. Those mentions have been removed.

Additionally, 1Password now supports signing Git commits with SSH keys and makes it pretty easy-plus you can easily configure Git Tower to use it for both signing and ssh.

For using a GUI-based GIT tool such as Tower or Github Desktop, follow the steps here for signing your commits with GPG.

Profiling performance

Using perf:

$ perf record -g binary
$ perf script | stackcollapse-perf.pl | rust-unmangle | flamegraph.pl > flame.svg

NOTE: See @GabrielMajeri's comments below about the -g option.

Moved to https://github.com/kbilsted/Functional-core-imperative-shell/blob/master/README.md

	// This is an advanced example! It is not typically required for application code.
	// If you are using a library like Redux or MobX, use the container component provided by that library.
	// If you are authoring such a library, use the technique shown below.

	// This example shows how to safely update subscriptions in response to props changes.
	// In this case, it is important to wait until `componentDidUpdate` before removing a subscription.
	// In the event that a render is cancelled before being committed, this will prevent us from unsubscribing prematurely.

	// We also need to be careful about how we handle events that are dispatched in between
	// `getDerivedStateFromProps` and `componentDidUpdate` so that we don't put stale values into the `state`.

	// This code implements a persistent dictionary similar to Map except the
	// internal representation is a Dictionary + diffs. This offers different
	// performance tradeoffs and, in particular, much faster add and remove when
	// used linearly.
	//
	// For more details, see the following articles from the F# Journal:
	//
	// http://fsharpnews.blogspot.co.uk/2017/10/the-concestor-set.html
	// http://fsharpnews.blogspot.co.uk/2017/10/a-simple-concestor-dictionary.html

	12602491 element?
	6960375 shen.pvar?
	3535830 shen.lazyderef
	3378725 fail
	2390069 shen.compose
	2087153 shen.deref
	2073332 shen.occurs?
	1900416 <-address/or
	1716707 assoc
	1513336 do

	// An implementation of what is decribed at:
	// https://nikhilm.github.io/uvbook/threads.html#id1

	#include <stdio.h>
	#include <string.h>
	#include <stdbool.h>
	#include <stdlib.h>
	#include <unistd.h>
	#include <uv.h>

	.cm
	/a.out