andrey pechorin pechorin

My issues with Modules

In researching topics for RailsCasts I often read code in Rails and other gems. This is a great exercise to do. Not only will you pick up some coding tips, but it can help you better understand what makes code readable.

A common practice to organize code in gems is to divide it into modules. When this is done extensively I find it becomes very difficult to read. Before I explain further, a quick detour on instance_eval.

You can find instance_eval used in many DSLs: from routes to state machines. Here's an example from Thinking Sphinx.

class Article &lt; ActiveRecord::Base

Введение

Начать стоит отсюда. Не пугайтесь то, что это книга по незнакомой OS, эти термины практически везде одинаковые и здесь они изложены в понятной для начинающих форме.

http://www.qnx.com/developers/docs/6.4.1/neutrino/getting_started/s1_procs.html

Прочесть нужно треть главы до подраздела "Starting a process", если С не пугает, читайте полностью. После прочтения вы будете понимать, что такое process, thread, mutex, priorites, semaphores, scheduler, contex-switch, kernel states.

Ruby

Frontend Development

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Pry Cheat Sheet

Youtube Tutorial 2013

Command Line

pry -r ./config/app_init_file.rb - load your app into a pry session (look at the file loaded by config.ru)
pry -r ./config/environment.rb - load your rails into a pry session

Debugger

	# example
	# date = Date.today
	# ExchangeWithFallback.new(
	# SynchronizedRates.new(
	# DoubleConvertThrough.new('RUB',
	# InverseRatesFor.new( {from: 'RUB'},
	# RatesUpdatedWithFallback.new(
	# ActiveRecordRates.new(CurrencyRate.where(date: date, bank: 'cbr')),
	# LazyRates.new { CentralBankOfRussia.new.update_rates(date) } )))))

	-- show running queries (pre 9.2)
	SELECT procpid, age(clock_timestamp(), query_start), usename, current_query
	FROM pg_stat_activity
	WHERE current_query != '<IDLE>' AND current_query NOT ILIKE '%pg_stat_activity%'
	ORDER BY query_start desc;

	-- show running queries (9.2)
	SELECT pid, age(clock_timestamp(), query_start), usename, query
	FROM pg_stat_activity
	WHERE query != '<IDLE>' AND query NOT ILIKE '%pg_stat_activity%'

	-- http://stackoverflow.com/questions/1124603/grouped-limit-in-postgresql-show-the-first-n-rows-for-each-group
	-- http://www.postgresql.jp/document/9.2/html/tutorial-window.html

	CREATE TABLE empsalary (
	depname varchar(10) not null
	, empno integer not null
	, salary integer not null
	);

	INSERT INTO empsalary (depname, empno, salary) VALUES ('develop', 11, 5200);

	# place in ./config/initializers
	# Usage
	# LL.warn "blah"
	# LL.warn @profile.inspect

	require 'pp'
	require 'log4r'
	require 'log4r/configurator'
	require 'log4r/yamlconfigurator'
	require 'log4r/outputter/fileoutputter'

	# ElasticSearch upstart script

	description "ElasticSearch service"

	start on (net-device-up
	and local-filesystems
	and runlevel [2345])

	stop on runlevel [016]

	# Idea from http://krautcomputing.com/blog/2012/10/07/how-to-make-everything-background-processable-through-sidekiq/
	#
	# Usage:
	#
	# class Synchronization
	# include Asyncable
	# end
	#
	# Then:
	# Synchronization.find(12).perform_async(:synchronize, 3, 2)