timvisee

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).

timvw

case class RemoteIteratorWrapper[T](underlying: org.apache.hadoop.fs.RemoteIterator[T]) extends scala.collection.AbstractIterator[T] with scala.collection.Iterator[T] {
  def hasNext = underlying.hasNext
  def next() = underlying.next()
}

object Conversions {
  implicit def remoteIterator2ScalaIterator[T](underlying: org.apache.hadoop.fs.RemoteIterator[T]) : scala.collection.Iterator[T] = RemoteIteratorWrapper[T](underlying)
}

Mic92

#!/bin/bash

if [[ "$1" != -S && "$1" != -S*u && "$1" != -U ]]; then
    /usr/bin/pacman "$@"
    exit $?
fi

[[ $EUID -eq 0 ]] && etckeeper pre-install

/usr/bin/pacman "$@"

earthgecko

#!/bin/bash
# bash generate random alphanumeric string
#

# bash generate random 32 character alphanumeric string (upper and lowercase) and 
NEW_UUID=$(cat /dev/urandom | tr -dc 'a-zA-Z0-9' | fold -w 32 | head -n 1)

# bash generate random 32 character alphanumeric string (lowercase only)
cat /dev/urandom | tr -dc 'a-z0-9' | fold -w 32 | head -n 1

hellerbarde

Latency numbers every programmer should know

L1 cache reference ......................... 0.5 ns
Branch mispredict ............................ 5 ns
L2 cache reference ........................... 7 ns
Mutex lock/unlock ........................... 25 ns
Main memory reference ...................... 100 ns             
Compress 1K bytes with Zippy ............. 3,000 ns  =   3 µs
Send 2K bytes over 1 Gbps network ....... 20,000 ns  =  20 µs
SSD random read ........................ 150,000 ns  = 150 µs

Read 1 MB sequentially from memory ..... 250,000 ns = 250 µs