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.

sudo gem install parallel

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

• 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

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

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

• [ActiveRecord] ActiveRecord::Base.connection.reconnect! inside the parallel block prevents errors
• [Benchmark/Test] Disable threading/forking with :in_threads => 0 or :in_processes => 0, great to test performance or to debug parallel issues

• JRuby / Windows support <-> possible ?

• Przemyslaw Wroblewski
• TJ Holowaychuk
• Masatomo Nakano
• Fred Wu
• mikezter
• Jeremy Durham
• Nick Gauthier
• Andrew Bowerman
• Byron Bowerman
• Mikko Kokkonen

Michael Grosser
[email protected]
Hereby placed under public domain, do what you want, just do not hold me accountable...