async_enum

Inspired by Enumerable#lazy coupled with Enumerator::Lazy, and the Async.js library, I thought it would be cool to have syntax like urls.async.map{ |url| http_get(url) }.

Runs In Parallel

require 'benchmark'

sync = Benchmark.measure do
	5.times.each{ sleep 0.1 }
end

async = Benchmark.measure do
	5.times.async.each{ sleep 0.1 }
end

puts sync, async
# 0.000000   0.000000   0.000000 (  0.500782)
# 0.000000   0.010000   0.010000 (  0.102763)

How It Works

The implementation was based on Enumerable#lazy introduced with Ruby 2.0. Enumerator::Async follows a similar approach, where the Enumerator is passed into the constructor.

enum = ('a'..'z').each

# the following are equivalent

Enumerator::Async.new(enum)
enum.async

To get the enumerator back from the async enumerator, simply call sync or to_enum like so:

enum.async.sync == enum
# => true

Every operation on the async enumerator affects the contained enumerator in the same way. For instance:

enum.with_index.to_a
# => [ ['a', 0], ['b', 1], ['c', 2] ... ]

enum.async.with_index.to_a
# => [ ['a', 0], ['b', 1], ['c', 2] ... ]

Async methods can be chained just like tipical enumerator methods:

enum.async.each{ sleep(0.1) }.each{ sleep(0.1) }

How to use it

The method Enumerable#async was added so that every collection can be processed in parallel:

[ 0, 1, 2 ].async.each{ |i| puts i }
(0..2).async.map(&:to_i)

# or chain to your heart's content

(0..5).reject(&:even?).reverse.async.with_index.map{ |x, index| x + index }

Limiting thread pool size

To limit the thread pool size, you can pass in an optional parameter to async. Suppose for performance reasons you want to use a maximum of 4 threads:

(0..100).async(4).each do
	# use bandwith
end

Preventing race conditions

When programming concurrently, nasty bugs can come up because some operations aren't atomic. For instance, incrementing a variable x += 1 will not necessarily work as expected. Use a lock when encountering these types of errors.

require 'async_enum'

count = 0
mutex = Mutex.new
('a'..'z').async.each do
  mutex.synchronize do
    count += 1
  end
end
count
# => 26

There used to be a lock DSL syntax, but it ruined using async_enum in scoped method calls.

Notes

To install it, add it to your gemfile:

# Gemfile

gem 'async_enum'

To run the demos, clone the project and run with the library included in the load path:

$ git clone git@github.com:aj0strow/async_enum
$ cd async_enum
$ ruby -I lib demos/sleep.rb

Contributions

Yoshida Tetsuya (@yoshida-eth0) fixed the fiber error issue, and made the gem work with hashes.

Please report errors and feel free to contribute and improve things!

aj0strow / async_enum