threach

threach adds to the Enumerable module to provide a threaded version of whatever enumerator you throw at it (each by default).

Warning: Deadlocks under JRuby if an exception is thrown

threach works fine, so long as nothing goes wrong. In particular, there's no safe way (that I can find; see below) to break out of a threach loop without a deadlock under JRuby. This is, shall we say, an Issue.

Under vanilla ruby, threach will exit as expected, but who the hell wants to use threach where there are no real threads???

Installation

threach is on rubygems.org, so you should just be able to do

gem install threach
# or jruby -S gem install threach

Use

# You like #each? You'll love...err.."probably like" #threach
require 'rubygems'
require 'threach'

# Process with 2 threads. It assumes you want 'each'
# as your iterator.
(1..10).threach(2) {|i| puts i.to_s}  

# You can also specify the iterator
File.open('mybigfile') do |f|
  f.threach(2, :each_line) do |line|
    processLine(line)
  end
end

# threach does not care what the arity of your block is
# as long as it matches the iterator you ask for

('A'..'Z').threach(3, :each_with_index) do |letter, index|
  puts "#{index}: #{letter}"
end

# Or with a hash
h = {'a' => 1, 'b'=>2, 'c'=>3}
h.threach(2) do |letter, i|
  puts "#{i}: #{letter}"
end

Major problem

I can't figure out how to exit gracefully from a threach loop.

begin ('a'..'z').threach(2, :each_with_index) do |letter, i| break if i > 10 # will deadlock under jruby; fine under ruby # raise StandardError if i > 10 # deadlock under jruby; find under ruby puts letter end rescue puts "Rescued; broke out of the loop" end

The break under jruby prints "Exception in thread "Thread-1" org.jruby.exceptions.JumpException$BreakJump," but if there's a way to catch that in the enclosing code I sure don't know how.

Use of catch and throw seemed like an obvious choice, but they don't work across threads. Then I thought I'd use catch within the consumers and throw or raise an error at the producer, but that doesn't work, either.

I'm clearly up against (or well beyond) my knowledge limitations, here.

If anyone has a solution to what should be a simple problem (and works under both ruby and jruby) boy, would I be grateful.

Why and when to use it?

Well, if you're using stock (MRI) ruby -- you probably shouldn't bother with threach. It'll just slow things down. But if you're using a ruby implementation that has real threads, like JRuby, this will give you relatively painless multi-threading.

You can always do something like:

if defined? JRUBY_VERSION
  numthreads = 3
else
  numthreads = 0
end

my_enumerable.threach(numthreads) {|i| ...}

Note the "relatively" in front of "painless" up there. The block you pass still has to be thread-safe, and there are many data structures you'll encounter that are not thread-safe. Scalars, arrays, and hashes are, though, under JRuby, and that'll get you pretty far.

Note on Patches/Pull Requests

Fork the project.
Make your feature addition or bug fix.
Add tests for it. This is important so I don't break it in a future version unintentionally.
Commit, do not mess with rakefile, version, or history. (if you want to have your own version, that is fine but bump version in a commit by itself I can ignore when I pull)
Send me a pull request. Bonus points for topic branches.