A simple way of doing heavy work in a background process and blocking until done when you really need the object.

Preloading using the proxy pattern Heavily inspired by Adam Sandersons post

Dunder

For tasks that can be started early and evaluated late.

Typically one might want start multiple heavy tasks concurrent. This is already solvable with threads or the reactor-pattern but setting this up could be cumbersome or require direct interactions with threads ex.

Dunder is a simple way of abstracting this: you simply pass a block to Dunder.load and Dunder will execute this in a thread behind the scenes. When later accessing the lazy_object will block until the thread is done and has returned or if the thread is done returns the value

The implementation itself relies only on the ruby standard library and is below 50 lines of code

Usage

lazy_object = Dunder.load {
	# heavy stuff
	value
}

or through dunder_load

lazy_sorted_articles = @articles.dunder_load.sort_by do |a|
	a.title
end

lazy_sorted_array = array.dunder_load.sort

lazy_obj = obj.dunder_load.do_something_heavy(a,b,c) {
	#maybe something other heavy here
}

Read more further down

lazy_foo = Dunder.load {
	# Simulate heavy IO
	sleep 2
	"foo" 
}

lazy_bar = Dunder.load {
	# Simulate heavy IO
	sleep 2
	"bar" 
}

# Do something other heavy

puts lazy_bar # => "bar"
puts lazy_bar.class # => String
puts lazy_foo # => "foo"
puts lazy_foo.class # => String
# Will finish after 2 seconds

worth mentioning is that if you access the variable in someway before that it will block earlier ex lazy_array = Dunder.load do sleep 1 [1,2,3] end puts lazy_array.length # <- will block here until the above sleep is done sleep 1 # other heavy stuff puts lazy_array # <- will be printed after 2 seconds

changing the order of the statements will fix this though

lazy_array = Dunder.load do
	sleep 1
	[1,2,3]
end
sleep 1 # other heavy stuff
puts lazy_array.length # <- will block here until the above sleep in the block is done
puts lazy_array # <- will be printed after 1 second

Rails

@lazy_posts = Dunder.load do
	Post.all
end
@lazy_users = Dunder.load do
	User.all
end

and then later in views

<%= @lazyposts.each do %> <- this will block until the posts have been loaded
...
<% end %>

Known problems

 Has only been tested with 1.9.2

Install

gem install dunder

(The MIT License)

Copyright (c) 2011 Erik Fonselius

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.