Alexey Bokov’s weblog

By unknown reasons Sun JDK was moved to partner repository, so to use sun jdk you need to do this steps

sudo add-apt-repository "deb http://archive.canonical.com/ lucid partner"
sudo apt-get update
sudo apt-get upgrade

and then enjoy :

sudo apt-cache search jdk | grep sun
sun-java6-source - Sun Java(TM) Development Kit (JDK) 6 source files
sun-java6-jre - Sun Java(TM) Runtime Environment (JRE) 6 (architecture independent files)
sun-java6-jdk - Sun Java(TM) Development Kit (JDK) 6
sun-java6-javadb - Java(TM) DB, Sun Microsystems' distribution of Apache Derby
sun-java6-demo - Sun Java(TM) Development Kit (JDK) 6 demos and examples
sun-java6-bin - Sun Java(TM) Runtime Environment (JRE) 6 (architecture dependent files)


• Shanghai releases 3-year cloud computing plan – Shanghai plans to use cloud computing technologies in urban management, industry development, e-government and small and medium-sized enterprise services

AWS related links :

• State of the cloud – 2010 August
• Amazon’s EC2 Generating 220M+ Annually – really interesting post – “at 40,000 servers evenly distributed across 6 availability zones we know, ___ 6,700 servers per zone..Most of the servers are likely in the US availability zones vs. the EU zones, maybe 75-80% of total capacity”. Also take a look on amazon ec2 instances usage rates
• Anatomy of an Amazon EC2 Resource ID and based on this anatomy EC2 usage estimates
• Rumor Mill: Google EC2 Competitor Coming in 2010?

You can use sed :

sed -e 's/\([^\d]*\)/\L\1/' in.txt > out.txt

or perl inliner :

perl -ne 'utf8::decode $_; $_ = lc $_; utf8::encode $_; print' in.txt > out.txt
.
Both guys works fine for unicode file too.

Using telnet in bash scripts to automate some stuff ? It’s really easy, here’s an example to tell “hello world” on telnet server :

req="hello world"
server="my_server 1234"
val=`( echo open ${server}
sleep 3
echo "${req}"
sleep 1 ) | telnet`
echo $val


Okay, we have text file with list of urls and want to have firefox’s screenshots from this pages and also we need to have this screenshots in some normalized resolution ( like all images should be in 300×400 – thumbnails ). First of all you need to install Command line print Firefox add-on. Then create some simple script which will run firefox with needed url, print screenshot and close ( in my case via kill – may be it’s too brutal ) firefox in cycle. It may look like this ( url_list.txt – file with urls – each url on its own line ), after running this script you will have many *.png files which is screenshots for ulrs – 0.png – for first url in urls_list.txt, 1.png for second and so on.

#!/bin/bash
id=0
while read line
do
firefox -print $line -printmode png -printdelay 10 -printfile ${id}.png
ps ax | grep firefox | awk '{ print $1 }' | xargs kill -9 ;
id=$[$id+1]
done < urls_list.txt


And now then we have screenshots ( all this guys are in different resolution in common ) then we need to normalize them – to create thumbnails for all images in 300×400 resolution – convert helps!

for f in *.png;
do
convert -thumbnail 300x400! ${f} thumb_${f}
done

And we have many thumb_*.pn with 300×400 resolution all. A little note – using resolution without ! sign will work in another way – resize will be processed proportionally with using resize only for one dimension ( bigger one ).

• Ten Tips for a (Slightly) Less Awful Resume
• How To Sell Agile To Fixed Bid Contract Clients
• AWS Launches Cluster Compute EC2 Instances For High Performance Applications and AWS – High Performance Computing (HPC)

GIT

• git for big files : git-bigfiles
• omit large files commiting into git repo : Rejecting large files in git
• git as backup system : A better backup system based on Git and Journey to a backup solution: Git
• Hosting Git repositories, The Easy (and Secure) Way

Subversion ( svn )

• How to store-all-stuff-in-svn : Subverting your homedir, or keeping your life in svn
• SVN-Hooks : Avoid empty comment in SVN commits
• Using SVN-Hooks to commit notifications on email : Setting up a post-commit mail notification for a Subversion repository
• SVN Notify documentation

Hash tables :

C++ Q/A :

Cloud computing is a term that originally meant elastic on demand computing but is now a term applied elastically by marketdroids to any form of virtualisation.
This is part of the transition from 2009′s vBullshit to BaaS, Bullshit as a Service.

via chapmancentral.demon.co.uk

• The Web as a graph by Ravi Kumar, Prabhakar Raghavan, Sridhar Rajagopalan,Eli Upfaly, Andrew S. Tomkins
• The Web as a graph: measurements, models, and methods
• Web Graph and PageRank algorithm by Danil Nemirovsky
• Parallel implementation of graph diameter algorithms
• Diameter of the World-Wide-Web
• Fast Computation of Empirically Tight Bounds for the Diameter of Massive Graphs Cl ?mence Magnien 1 , Matthieu Latapy 1 and Michel Habib
• Structural Analysis of the Web
• Small world phenomenon
• Fast Radius Plot and Diameter Computation for Terabyte Graphs (SDM 2010)
• Probabiblistic Counting algorithms for Database applications by Philippe Flajolet
• Philippe Flajolet home page
• HADI: Fast Diameter Estimation and Mining in Massive Graphs with Hadoop
• U Kang personal home page – one of HADI authors
• Data Mining with M AP R EDUCE: Graph and Tensor Algorithms with Applications
• PEGASUS: Mining Peta-Scale Graphs

Here’s some stuff about ( yeah, I know – ‘geeks, stop migrating from svn and git and vise versa – just developer code and don’t spent time on this!‘ ) svn and git comparison.

What do we have : git and svn installed on a same server, empty both svn and git repositories – I will add same data and provide same changes in both repositories,  and also, in another folder, I will checkout how update changes works – so in this tests I’m going to figure out how it works for ‘commiters’ and for ‘those who update changes’. My tests deal with  typical operations with version control systems  – checkout time for adding, pushing and pulling various types of data and checkout how update for them will work – test’s detailed information is below table. For git I use git+ssh protocol, for svn I use svn protocol. I don’t provide any special configuration nor for git nor for svn – all settings is about to be default. Also I would like to note that this tests is partially incomplete – I don’t checkout how delete, branching, merging and some other functions works – so in future I will try to add these points onto this test. Main result of this test – git is faster than svn about a 2-3 times in typical configuration. There’s only one really bad points – git works bad on pretty big files ( > 300 mb size), for some big size ( ~1gb ) it git even can exit with error about memory leak – there’s some special git-related project – like git-bigfiles – this stuff should help you to work with git and big files together.

So – In common we have that git is about 2.6 faster than svn.

I understand that this is may be very non-precious tests and also I don’t check how delete or branching works, but anyway I checkout my own most used operations during this test. In common we can see that git is more than 2 times faster than svn – everything looks fine with git, except one really bad thing  – work with big ( more than 100 mb size ) files – for this type of file svn is really works faster, and for too big ( more than 1 GB files ) git even crashed during ‘git push’ command with ‘fatal: Out of memory, malloc failed‘ message.

Test1 boost 1_43 C++ library :  29135 files and 31609 objects including folders, 286 Mb summary size

Test 3
I just add first line to some cpp files :

find ./ -name "*a???.cpp" -exec sed -i 1i"//test comment `date` : {}" {} \;


Test 5
Change all *.cpp files in the same way :

find ./ -name "*.cpp" -exec sed -i 1i"//big test comment2 `date` : {}" {} \;


Test 7:  Add  real-life repository :  many sources in cpp, perl, erlang, makefiles, bash scripts, MS word documents, images, pdf’s, compiled binaries, resource files, etc,  in sum it contains 4605 files, size is about 2.6G

Test 9:
Refactoring simulation : make to use “std::” specifier for all cerr and cout. Not sure it’s really safe in real-life-development, but it’s okay for test purpose.

find ./ -name "*.h"   -exec sed -i "s/  cerr/std::cerr/g" {} \;
find ./ -name "*.cpp" -exec sed -i "s/ cerr/std::cerr/g" {} \;
find ./ -name "*.cpp" -exec sed -i "s/ cout/std::coutr/g" {} \;


Test 11:  checkout whole project

Test 12: adding 50 mb text file – apache logs

Test 14: adding 72 mb file – many c++ sources concantenated in one big file

Test 16: small xml : 100 mb – xml file sample from real life

Test 18: medium xml : 300 mb – same ( but bigger ) real-life xml fil

Test 20: large xml : 1200 mb – sample of pretty big real-life xml

git push failed with error message of memory leak ( as I can see ) : “fatal: Out of memory, malloc failed”

I collect some usefull information about different source text repositories version control systems : git, svn, cvs, mercury links – take a look on this if you’re interested in different VCS system using.

Since middle of April 2010 I’m work with redmine as corporate wiki in my company – we choose redmine mostly because it’s free, open-source and pretty popular – we don’t need to provide any accounting stuff to buy it officially and in case of some troubles we can find solution in redmine user’s community ( or fix it by ourselft – it’s written on Ruby btw ). As some minus of redmine I can note that redmine don’t really have very detailed documentation – some stuff is skipped and you need to figure out it by yourselft. So in this post I will share my own tips and trick as redmine active user.

• Using anchors in redmine
• Usefull tips for table formatting in redmine
• How to use HTML tags in your redmine wiki documents ?
• Redmine usefull links

Using anchors in redmine

There’s no {anchor} macro in redmine ( Confluence wiki got it btw ) – instead of this you can use h1, h2 or h3 tags ( but not h4 ! ) – header text will be used by redmine as anchor text. Also if your anchor text contains space you need to replace this spaces (in link ) by minus sign. Also I can note that it’s looks that anchor texts isn’t case sensitive. Here’s some examples which can help you figure out it better :
Here’s some anchors from current page to page with name “my test page” which contains anchors “Hello wordl!” and “test”, so page which contain links is looks like :

[[my_test_page#Hello-world|Hello world]] - link to hello world section on my test page
[[my_test_page#test|test]] - link to test section on my test page

And page to which we refer it something about :

h1. Hello world
Some thing about ANSI C.
h2. Test
Something about test>

Again I would like to note that only h1,h2, h3 tags will be treated as anchors, not h4. Also you can’t use header with “!” or “?” because you will have troubles with referring anchor to it ( I mean “h1. Hello world!” won’t create proper anchor is I can see from my experience ).

Usefull tips for table formatting in redmine

Here’s a link : Redmine: Create Tables Using Textile Formatting

How to use HTML tags in your redmine wiki documents ?

It’s really easy – go to file redcloth3.rb ( in my installation it located in /opt/redmine/lib/redcloth3.rb ) and change line onto adding tags which you would like to use. For example to enable <br>
and <a>  it’s enough to change it line which contains ALLOWED_TAGS initialization with your tags. Originally it was ( in my case this stuff located in 1187 line )
ALLOWED_TAGS = %w(redpre pre code notextile)


and I just it change to

ALLOWED_TAGS = %w(redpre pre code notextile br a)

To apply this changes don’t forget to restart web server – after this you will be able to use <a>.. </a> as they should be in HTML your redmine wiki pages. Also allowing tag <a> ( and as result enable <a name=”#my_anchor_text”> )will give an unlimited possibility to put anchors on wiki pages on any place which you like, for example in middle of tables.

Redmine usefull links

• Redmine installation : Zero to Redmine in 22 Steps

• Mapreduce & Hadoop Algorithms in Academic Papers (3rd update), especially Scaling Up Classifiers to Cloud Computers
• TeamBox – project collaboration tool
• Continuous Integration for C++ by Rick Wagner
• Beyond Position Bias: Examining Result Attractiveness as a Source of Presentation Bias… Yue, Patel, Roehrig, WWW-2010

.. to be continued

Q1: What value will be printed ?
double d1 = 16, d2=2.0;
double d3 = (1/2) * ( sqrt(d1) + d2/2);
cout << d3 << endl;


Q2: Please write your own itoa implementation

Q3: What is pure virtual destructor? Shall ( or can ) pure virtual functions be implemented ?

Q4: Give an example of abort function implementation

Q5: Why we need semicolon after closing bracket in C++ class declaration ?

Q6: Can we call destructor directly? For what we may need it ?

Q7: Can we call constructor directly? For what we may need it ?

Q8: Can we thron an exception in destructor ?

Q9: What happen if we call pure virtual methods in constructor or destructor ? Same question about ‘non-pure’ virtual methods ?

Q10: Why don’t we have virtual constructors in C++ ?

Q11: What is difference between new and new [] ? Same thing about delete and delete [] ?

Q12: What is a difference between static_cast, dynamic_cast, reinterpret_cast and const_cast ?

Q13: Why do we need explicit keyword in C++ ?

Q14: Explain difference between

const MyClass c;
const MyClass &c2 = c;
const MyClass *c2 = &c;
const MyClass * const c2 = &c;


Q15: Difference between const_iterator and iterator

Q16: Implement Rand5 ( which returns randomly 0..4 ) use only Random7 ( which returns 0..6)

Q17: Can we use object of class ( or structure ) which doesn’t have name? Can we declare and use classes and structures without names ?

Q18: What is it factory pattern ?

( to be updated and continued very soon

Answers ( if you need it ) below Continue reading ‘C/C++ interview questions’ »

Some usefull highlights which looks interested for me from Laws of productivity : 8 productivity experiments you don’t need to repeat (if this link doesn’t work please use this link onto copy hosted on bokov.net) – simple thoughts which may help you to organize process better and make it more efficient. Continue reading ‘Laws of productivity : 8 productivity experiments you don’t need to repeat’ »

Using json in bash :

• jsawk : work with an array of JSON objects read from stdin, filter them using JavaScript to produce a results array that is printed to stdout. For example get’s json ( from Yahoo image search by ‘madonna’ query ) and add some info ( madonna’s real name ) to this

wget http://bokov.net/json_example.json
cat json_example.json | ./jsawk "this.ResultSet.RealName=\"Louise Ciccone\"" > updated_info.json


• you can use some bash/awk/sed stuff to parse json. For example – list all image urls from json

wget http://bokov.net/json_example.json
cat json_example.json | sed -e 's/[{}]/''/g' | awk -v k="text" '{n=split($0,a,","); for (i=1; i<=n; i++) print a[i]}' | grep '"ClickUrl":' | sed 's/:/ /1' | awk -F" " '{ print $2 }'


• or use library from json.org for language which you like

via v.kruchkov

We have git repo at github (  and would like to move onto some our corporate box inside our network, for example on internal.bokov.net. This repository is shared for group of developers and all who have ssh access onto internal.bokov.net shall have right to commits onto git repository. So first of all prepare place for git repo at new hosting :

ssh user@internal.bokov.net
cd var
mkdir git_repo
chmod 777 git_repo
cd git_repo
mkdir my_project
cd my_project
git init --bare --shared=all
cd objects
chmod g+ws *


Next clone existing repo and change its settings to point onto internal.bokov.net

git clone --bare git@github.com:bokov/github_project.git
git remote add -t master -m master origin ssh://internal.bokov.net/var/git_repo/my_project/
git push origin master


to start work with new repo just use

git clone ssh://internal.bokov.net/var/git_repo/my_project/


have fun.

• Ubuntu doesn’t asking for login after boot up ( may happen after unexpected shutdown ) :
  press Ctrl-Alt-F1 to login in terminal mode and use fsck to fix it
• Add user short memo :
[root@my-box ~]# useradd -g users -u 560 tuser
[root@my-box ~]# passwd tuser

  ps. sudo will be required in not-root case
• Proper access rights for .ssh files :
chmod 700 ~/.ssh
chmod 600 ~/.ssh/id_rsa
chmod 644 ~/.ssh/id_rsa.pub
chmod 644 ~/.ssh/authorized_keys
chmod 644 ~/.ssh/known_hosts

• List all files in folder sorted by size :
find . -type f -exec du -k "{}" \; | sort -n


The US military has announced plans to buy 2,200 more of the game consoles, so that they can massively beef up the processing power of an existing, PS3-based supercomputer. A “Justification Review Document,” which has oddly been deleted from Google since I found it but is still available at this cache link, explains that, “the new PS3s will be placed in a cluster environment with an existing cluster of 336 PS3s by connecting each of the units’ one gigabit Ethernet port to a common 24 port gigabit hub.”
via arstechnica.com