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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(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

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

Tips

  • [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

TODO

  • JRuby / Windows support <-> possible ?

Authors

Contributors

Michael Grosser
michael@grosser.it
License: MIT
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