Run any code in parallel Processes(> use all CPUs) or Threads(> speedup blocking operations).
Best suited for map-reduce or e.g. parallel downloads/uploads.

Install

sudo gem install parallel

Usage

# 2 CPUs -> work in 2 processes (a,b + c)
results = Parallel.map(['a','b','c']) do |one_letter|
  expensive_calculation(one_letter)
end

# 3 Processes -> finished after 1 run
results = Parallel.map(['a','b','c'], :in_processes=>3){|one_letter| ... }

# 3 Threads -> finished after 1 run
results = Parallel.map(['a','b','c'], :in_threads=>3){|one_letter| ... }

Same can be done with each Parallel.each(['a','b','c']){|one_letter| ... } or each_with_index or map_with_index

Processes

• Speedup through multiple CPUs
• Speedup for blocking operations
• Protects global data
• Extra memory used ( very low on REE through copy_on_write_friendly )
• Child processes are killed when your main process is killed through Ctrl+c or kill -2

Threads

• Speedup for blocking operations
• Global data can be modified
• No extra memory used

ActiveRecord

Try either of those to get working parallel AR

Parallel.each(User.all, :in_threads => 8) do |user|
  ActiveRecord::Base.connection_pool.with_connection do
    user.update_attribute(:some_attribute, some_value)
  end
end

Parallel.each(User.all, :in_processes => 8) do |user|
  ActiveRecord::Base.connection.reconnect!
  user.update_attribute(:some_attribute, some_value)
end

Processes/Threads are workers, they grab the next piece of work when they finish

Progress / ETA

require 'progressbar'
progress = ProgressBar.new("test", 100)
Parallel.map(1..100, :finish => lambda { |i, item| progress.inc }) { sleep 1 }
progress.finish

Tips

• [Benchmark/Test] Disable threading/forking with :in_threads => 0 or :in_processes => 0, great to test performance or to debug parallel issues

TODO

• JRuby / Windows support <-> possible ?

Authors

Contributors

• Przemyslaw Wroblewski
• TJ Holowaychuk
• Masatomo Nakano
• Fred Wu
• mikezter
• Jeremy Durham
• Nick Gauthier
• Andrew Bowerman
• Byron Bowerman
• Mikko Kokkonen
• brian p o'rourke
• [Norio Sato]
• Neal Stewart
• Jurriaan Pruis
• Rob Worley
• Tasveer Singh

Michael Grosser
michael@grosser.it
License: MIT