zeeshanlakhani

Erlang Tracing: more than you wanted to know

Rough Outline

• What can be traced?
• How can trace events be specified?
• "match specifications": twisty passages, all alike
• WTF, can I just use DTrace and drink my coffee/beer/whisky in peace?
• Trace delivery mechanisms: pick one of two

zeeshanlakhani

Latency Comparison Numbers
--------------------------
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
Send 1K bytes over 1 Gbps network        10,000   ns    0.01 ms
Read 4K randomly from SSD*              150,000   ns    0.15 ms

zeeshanlakhani

Testing Stateful Code

So far, all the properties we have written have tested stateless code. Stateless code is made up of pure functions and is inherently easier to test than stateful code with side effects. The chief problem with testing stateful code is that the input to output mapping depends on the current state of the program. Previous operations can cause the same function to return different output given the same input. Therefore, in order to test stateful code, our tests must maintain some state of their own. This state is known as the model state and is updated as part of the testing process.

zeeshanlakhani

Keybase proof

I hereby claim:

• I am zeeshanlakhani on github.
• I am zeeshanlakhani (https://keybase.io/zeeshanlakhani) on keybase.
• I have a public key whose fingerprint is 1AC6 B34F BA77 A396 AB72 6F85 5D47 A705 052B 85B3

To claim this, I am signing this object:

zeeshanlakhani

# List of all the valid pdf URLs ever posted to the #Clojure IRC channel.
#
# Many of them are interesting CS papers others are not that useful. What I've done:
#
# 1. crawled an IRC history archive for the channel
# 2. extract pdf list in a file with: grep -riIohE 'https?://[^[:space:]]+pdf' * > pdf-links.txt
# 3. remove dupes: cat pdf-links.txt | sort | uniq > pdf-links-uniq.txt
# 4. filter only HTTP 200: cat pdf-links-uniq.txt | xargs curl -o /dev/null --connect-timeout 2 --silent --head --write-out '%{http_code} %{url_effective}\n' | grep "^200" > valid-pdf-links.txt
# 
# Now your choice to download them all or not. If you want, use: cat valid-pdf-links.txt | awk '{print $2}' | xargs wget

zeeshanlakhani

Description

This simple script will take a picture of a whiteboard and use parts of the ImageMagick library with sane defaults to clean it up tremendously.

The script is here:

#!/bin/bash
convert "$1" -morphology Convolve DoG:15,100,0 -negate -normalize -blur 0x1 -channel RBG -level 60%,91%,0.1 "$2"

Results

zeeshanlakhani

USING: kernel math sequences ;
IN: euler1

: multiple-of ( x y -- z ) mod zero? ;

: euler1 ( x -- y )
    1 - iota [ 1 + ] map
    [ dup [ 3 multiple-of ] [ 5 multiple-of ] bi or [ ] [ drop 0 ] if ]
    map
    sum

zeeshanlakhani

four primitives: run*, ==, conde, fresh

(run* (q)
  (== q #t))

; for what values of q is q equal to true?

answer: q must also be #t, so
'(#t)    ; answer comes back in a list

zeeshanlakhani

# time
# ====

macro time(ex)
    quote
        local t0 = time_ns()
        local val = $(esc(ex))
        local t1 = time_ns()
        println("elapsed time: ", (t1-t0)/1e9, " seconds")
        val

zeeshanlakhani

(ns markerbot.core
 (:require [taoensso.timbre :as log]
           [clojure.data.json :as json]
           [clojure.string :as s]
           [clj-http.client :as client])
  (:import (java.net Socket)
           (java.io PrintWriter InputStreamReader BufferedReader))
  (:gen-class))

;; marksy