Module: PMap

Included in:
Enumerable
Defined in:
lib/pmap.rb

Defined Under Namespace

Classes: DummyOutput

Class Method Summary collapse

Class Method Details

.included(base) ⇒ Object 



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# File 'lib/pmap.rb', line 12

def self.included(base)
  base.class_eval do
    # Parallel "map" for any Enumerable.
    # Requires a block of code to run for each Enumerable item.
    # [thread_count] is number of threads to create. Optional.
    def pmap(thread_count=nil, &proc)
      in_array = self.to_a        # I'm not sure how expensive this is...
      out_array = Array.new(in_array.size)
      process_core(thread_count, in_array, out_array, &proc)
      out_array
    end

    def process_core(thread_count, in_array, out_array, &proc)
      thread_count = thread_count(thread_count, in_array)
      size = in_array.size

      semaphore = Mutex.new
      index = -1                  # Our use of index is protected by semaphore

      threads = (0...thread_count).map {
        Thread.new {
          i = nil
          while (semaphore.synchronize {i = (index += 1)}; i < size)
            out_array[i] = yield(in_array[i])
          end
        }
      }
      threads.each {|t| t.join}
    end
    private :process_core

    def thread_count(user_requested_count, items)
      user_requested_count ||= $pmap_default_thread_count
      raise ArgumentError, "thread_count must be at least one." unless
        user_requested_count.respond_to?(:>=) && user_requested_count >= 1
      [user_requested_count, items.size].min
    end
    private :thread_count

    # Parallel "each" for any Enumerable.
    # Requires a block of code to run for each Enumerable item.
    # [thread_count] is number of threads to create. Optional.
    def peach(thread_count=nil, &proc)
      process_core(thread_count, self.to_a, DummyOutput.new, &proc)
      self
    end
  end
end