mpilquist

// Save as ~/.ammonite/predef.sc
// To use fs2 from ammonite repl, type `load.fs2` from repl prompt.
// You'll get all fs2 & cats imports, ContextShift and Timer instances
// for IO, and a globalBlocker

import $plugin.$ivy.`org.typelevel:::kind-projector:0.11.0`

if (!repl.compiler.settings.isScala213)
  repl.load.apply("interp.configureCompiler(_.settings.YpartialUnification.value = true)")

djspiewak

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

djspiewak

Thread Pools

Thread pools on the JVM should usually be divided into the following three categories:

1. CPU-bound
2. Blocking IO
3. Non-blocking IO polling

Each of these categories has a different optimal configuration and usage pattern.

osterman

#!/bin/bash -uxe

VERSION=2.7.13.2713
PACKAGE=ActivePython-${VERSION}-linux-x86_64-glibc-2.3.6-401785

# make directory
mkdir -p /opt/bin
cd /opt

wget http://downloads.activestate.com/ActivePython/releases/${VERSION}/${PACKAGE}.tar.gz

colophonemes

CREATE TRIGGER person_notify AFTER INSERT OR UPDATE OR DELETE ON income
FOR EACH ROW EXECUTE PROCEDURE notify_trigger(
  'id',
  'email',
  'username'
);

CREATE TRIGGER income_notify AFTER INSERT OR UPDATE OR DELETE ON income
FOR EACH ROW EXECUTE PROCEDURE notify_trigger(
  'id',

brandonroberts

import {Injectable, NgModuleFactory, NgModuleFactoryLoader, Compiler, Type} from '@angular/core';

class LoaderCallback {
  constructor(public callback) {}
}

export let load: Type = (callback: Function) => {
  return new LoaderCallback(callback);
};

jvandijk

-- Theme generated by vim2theme

Description = "vim darcula"

Default = { Colour="#a9b7c6" }
Canvas  = { Colour="#2b2b2b" }
Number  = { Colour="#6897bb" }
Escape  = { Colour="#cc7832" , Italic=true}
String  = { Colour="#a5c25c" }
BlockComment   = { Colour="#808080" }

jboner

Latency Comparison Numbers (~2012)
----------------------------------
L1 cache reference                           0.5 ns
Branch mispredict                            5   ns
L2 cache reference                           7   ns                      14x L1 cache
Mutex lock/unlock                           25   ns
Main memory reference                      100   ns                      20x L2 cache, 200x L1 cache
Compress 1K bytes with Zippy             3,000   ns        3 us
Send 1K bytes over 1 Gbps network       10,000   ns       10 us
Read 4K randomly from SSD*             150,000   ns      150 us          ~1GB/sec SSD

mumoshu

import java.io.File
import java.io.FileInputStream

case class Chunk(length: Int, bytes: Array[Byte])

def fileContentStream(fileIn: FileInputStream): Stream[Chunk] = {
  val bytes = Array.fill[Byte](1024)(0)
  val length = fileIn.read(bytes)
  Chunk(length, bytes) #:: fileContentStream(fileIn)
}