#.find

[kochd]

I got a expensive calculation and i want to kill all childs once one of them delivers a result:

results = Parallel.find(1..32, in_processes: 32) do
  this_could_take_long(1, 2)
end
p results #=> ["solution"]

Use case is solving a proof of work. One of the 16 processes will be the fastest and only one solution is needed. There seams to be no way to this or is ?

[grosser]

check how Parallel.any? is implemented ... .find should be very similar ...

[grosser]

... not sure if it's actually being lazy though ... there is support to raise Parallel::Break, just not sure how to also get the returned value ... that could be stored in the exception though, like raise Parallel::Break, result

[ellcs]

I've made an implementation. It's a bit hacky and would be happy to get some feedback. Before i make a pull request, i'd like to mention that Enumerable#find does actually not return the result, but the found element. So we need another name. While scrolling through the Array Documentation and Enumerable Documentation i did not find a matching name.

What do you think about the following names:

block = lambda { |e| if e > 2; e; end }
Parallel.first_result([1,2,3], &block) 
Parallel.find_first_result([1,2,3], &block) 
Parallel.first_done([1,2,3], &block) 

[grosser]

usually this is done with [1,2,3].find { |x| break x if x.even? } so let's implement that inferface :)

[ellcs]

I don't want to start a dicussion, but... :)

I have some thoughts on your suggested interface [1,2,3].find { |x| break x if x.even? }:

• The break x does not return x as you can see in the example below. It still returns the found element. So you actually do not need the break in the block and it has the same functionallity as { |x| x.even? }.

  block = lambda { |x| break(x*9) if x > 5 }
  (1..10).find(&block)
  # => 6

• find is not intended to return the calculated value, but the element. Using that method name could lead to confusion.
• I've implemented Rubys find aswell, but it returns the matching element, not the result. Have a look at 21b385e.

[grosser]

(1..10).find { break 111 } works though 🤷

[grosser]

... I guess the break might not be usable from inside parallel :/

[grosser]

lib/parallel.rb:445:in fork': unexpected break`
yeah :(

[grosser]

find_result sounds the best to me 👍

[grosser]

... but breaking with a value could also be simple