Monday, November 21, 2011

Ruby Sinatra web apps with background work threads

In Java-land, I have often used the pattern of writing a servlet with an init() method that starts up one or more background work threads. Then while my web application is handling HTTP requests the background threads can be doing work like fetching RSS feeds for display in the web app, perform periodic maintenance like flushing old data from a database, etc. This is a simple pattern that is robust and easy to implement with a few extra lines of Java code and an extra servlet definition in a web.xml file.

In Ruby-land this pattern is even simpler to implement:

require 'rubygems'
require 'sinatra'

$sum = 0

Thread.new do # trivial example work thread
  while true do
     sleep 0.12
     $sum += 1
  end
end

get '/' do
  "Testing background work thread: sum is #{$sum}"
end
While the main thread is waiting for HTTP requests the background thread can do any other work. This works fine with Ruby 1.8.7 or any 1.9.*, but I would run this in JRuby for a long-running production app since JRuby uses the Java Thread class.

3 comments:

YongMin Lee said...

Hi Mark
That source code is not working my source code..

require 'sinatra'
require 'rest_client'
require 'data_mapper'
require 'nokogiri'
require 'json'
require 'open-uri'
require 'sinatra/flash'
require 'will_paginate'
require 'will_paginate/array'
require 'date'
require 'time'
require 'thread'

DataMapper::setup(:default, "sqlite3://#{File.dirname(__FILE__)}/a.db")

class Ladder_data
include DataMapper::Resource
property :id, Serial
property :time, String
property :times2, String
property :start_point, String
property :ladder_type, String
property :answer, String

validates_uniqueness_of :times2
end

DataMapper.finalize
Ladder_data.auto_upgrade!
Thread.new do # trivial example work thread
while true do
$t=Time.now
$t=$t.min
$t=$t%2

if $t==0

a = JSON.parse( open("http://named.com/page/ladder/ajax/result.php").read )
b=a['times']
z=a['times2']
ladder = Ladder_data.new
ladder.time = b
ladder.times2 = z

c=a['start_point']
if c == 'first'
ladder.start_point = '왼쪽'
else
ladder.start_point= '오른쪽'
end

d=a['ladder_type']

if d == 'type1'
ladder.ladder_type ='3'
else
ladder.ladder_type = '4'
end

e=a['answer']
if e == 'EVEN'
ladder.answer='짝'
else
ladder.answer= '홀'
end
ladder.save

end
end
end


this is my source code.

Mark Watson, author and consultant said...

I am not sure why your code does not work. One thing to try: copy your code, and remove all database calls, making it simple - then see if threads work for you. Also, are you running on Linux or OS X?

Unknown said...

If you try to access the same data in another thread (e.g. in a sinatra route) you had better use a mutex!

require 'rubygems'
require 'sinatra'
require 'thread'

$sum = 0
$semaphore = Mutex.new

Thread.new do # trivial example work thread
while true do
sleep 0.12
$semaphore.synchronize { $sum += 1 }
end
end

get '/' do
$semaphore.synchronize { $sum += 10 }
"Testing background work thread: sum is #{$sum}"
end