CompTree — Parallel Computation Tree

Synopsis

  require 'comp_tree'

  CompTree.build do |driver|

    # Define a function named 'area' taking these two arguments.
    driver.define(:area, :width, :height) { |width, height|
      width*height
    }

    # Define a function 'width' which takes a 'border' argument.
    driver.define(:width, :border) { |border|
      7 + border
    }

    # Ditto for 'height'.
    driver.define(:height, :border) { |border|
      5 + border
    }

    # Define a constant function 'border'.
    driver.define(:border) {
      2
    }

    # Compute the area using four parallel threads.
    puts driver.compute(:area, :threads => 4)
    # => 63

    # We've done this computation.
    puts((7 + 2)*(5 + 2))
    # => 63
  end

Notes

The user should have a basic understanding of functional programming (see for example en.wikipedia.org/wiki/Functional_programming) and the meaning of side effects.

CompTree requires the user to adopt a functional style. Every function you define must explicitly depend on the data it uses.

  #
  # BAD example: depending on state -- offset not listed as a parameter
  #
  driver.define(:area, :width, :height) { |width, height|
    width*height - offset
  }

Unless offset is really a constant, the result of driver.compute(:area, :num_threads => n) is not well-defined for n > 1.

Just as depending on some changeable state is bad, it is likewise bad to affect a state (to produce a side effect).

  #
  # BAD example: affecting state
  #
  driver.define(:area, :width, :height) { |width, height|
    ACCUMULATOR.add "more data"
    width*height
  }

Given a tree where nodes are modifying ACCUMULATOR, the end state of ACCUMULATOR is not well-defined. Moreover if ACCUMULATOR is not thread-safe, the result will be even worse.

Note however it is OK affect a state as long as no other function depends on that state. This is the principle under which comp_tree parallelizes Rake tasks (drake.rubyforge.org).

Install

  % gem install comp_tree

Or for the regular (non-gem) .tgz package,

  % ruby install.rb [--uninstall]

Author

James M. Lawrence <quixoticsycophant@gmail.com>

License

  Copyright (c) 2008 James M. Lawrence.  All rights reserved.

  Permission is hereby granted, free of charge, to any person
  obtaining a copy of this software and associated documentation files
  (the "Software"), to deal in the Software without restriction,
  including without limitation the rights to use, copy, modify, merge,
  publish, distribute, sublicense, and/or sell copies of the Software,
  and to permit persons to whom the Software is furnished to do so,
  subject to the following conditions:

  The above copyright notice and this permission notice shall be
  included in all copies or substantial portions of the Software.

  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
  BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
  ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
  CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  SOFTWARE.