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Run all possible enumerable methods in concurrent/parallel threads.

urls.in_threads(20).map do |url|


Add the gem to your Gemfile...

gem 'in_threads'

...and install it with Bundler.

bundle install

Or install globally:

gem install in_threads


Let's say you have a list of web pages to download.

urls = [

You can easily download each web page one after the other.

urls.each do |url|

However, this is slow, especially for a large number of web pages. Instead, download the web pages in parallel with in_threads.

require 'in_threads'

urls.in_threads.each do |url|

By calling in_threads, the each web page is downloaded in its own thread, reducing the time by almost 4x.

By default, no more than 10 threads run at any one time. However, this can be easily overriden.

# Read all XML files in a directory
Dir['*.xml'].in_threads(100).each do |file|

Predicate methods (methods that return true or false for each object in a collection) are particularly well suited for use with in_threads.

# Are all URLs valid?
urls.in_threads.all? { |url| HTTP.get(url).status == 200 }

# Are any URLs invalid?
urls.in_threads.any? { |url| HTTP.get(url).status == 404 }


All methods of Enumerable with a block can be used if block calls are evaluated independently, so following will

all?, any?, collect_concat, collect, count, cycle, detect, drop_while, each_cons, each_entry, each_slice, each_with_index, each_with_object, each, enum_cons, enum_slice, enum_with_index, filter_map, filter, find_all, find_index, find, flat_map, group_by, map, max_by, min_by, minmax_by, none?, one?, partition, reject, reverse_each, select, sort_by, sum, take_while, to_h, to_set, uniq, zip.

Following either don't accept block (like first), depend on previous block evaluation (like inject) or return an enumerator (like chunk), so will simply act as if in_threads wasn't used:

chain, chunk_while, chunk, compact, drop, entries, first, include?, inject, lazy, max, member?, minmax, min, reduce, slice_after, slice_before, slice_when, sort, take, tally, to_a.

Break and exceptions

Exceptions are caught and re-thrown after allowing blocks that are still running to finish.

IMPORTANT: only the first encountered exception is propagated, so it is recommended to handle exceptions in the block.

break is handled in ruby >= 1.9 and should be handled in jruby 9.1 after and 9.2 and 9.3 after #7009. Handling is done in special way: as blocks are run outside of original context, calls to break cause LocalJumpError which is caught and its result is returned.

Copyright (c) 2009-2022 Ivan Kuchin. See LICENSE.txt for details.