Promise

Lightweight Ruby MRI promise extension (c) 2010 Lourens Naudé (methodmissing), James Tucker (raggi), tmm1 && ice799 for pointers (pun intended)

http://github.com/methodmissing/promise

** WORK IN PROGRESS **

This library works with Ruby 1.8 (1.9 pending) and is a more efficient implementation of the following Ruby code :

class Promise def initialize(&blk) @thread = Thread.new(&blk) @result = nil end

def method_missing(meth, *args)
  @result ||= @thread.value
end

end

Examples :

promise = Promise.new{ 1000.times{ IO.read(FILE) } } assert_equal 1000, promise.id # blocks only if we don't have a result from the computation thread yet

Challenges :

• Avoiding method_missing overhead, which bogs down even 1.9's BasicObject for this use case
• rb_define_method(rb_cPromise, "send", rb_promise_result_argc_any, -1);
• We attempt to negate some of that by overloading common Object members at compile time
• Ideally one should overload rb_call (block the current thread) and thus a Promise implementation is best served as a MRI patch.

Todo :

• ruby 1.9 support
• Fiber support
• reduce further method call overhead
• look into a symbol table for caching

Performance :

methodmissing:promise lourens$ rake bench (in /Users/lourens/projects/promise) /Users/lourens/.rvm/rubies/ruby-1.8.7-p249/bin/ruby bench/promise.rb Rehearsal -------------------------------------------------------------------- Promise 0.010000 0.000000 0.010000 ( 0.018255) RubyPromise 0.030000 0.000000 0.030000 ( 0.024190) Promise#== 0.010000 0.000000 0.010000 ( 0.017622) RubyPromise#== 0.020000 0.010000 0.030000 ( 0.020867) Promise#object_id 0.010000 0.000000 0.010000 ( 0.016699) RubyPromise#object_id 0.020000 0.000000 0.020000 ( 0.021970) Promise#send 0.020000 0.000000 0.020000 ( 0.017142) RubyPromise#send 0.020000 0.000000 0.020000 ( 0.021984) Promise (blocking) 0.040000 0.030000 0.070000 ( 0.072591) RubyPromise (blocking) 0.050000 0.030000 0.080000 ( 0.077348) Promise#== (blocking) 0.050000 0.030000 0.080000 ( 0.068011) RubyPromise#== (blocking) 0.050000 0.020000 0.070000 ( 0.084727) Promise#object_id (blocking) 0.050000 0.030000 0.080000 ( 0.069918) RubyPromise#object_id (blocking) 0.050000 0.030000 0.080000 ( 0.082319) Promise#send (blocking) 0.040000 0.020000 0.060000 ( 0.071780) RubyPromise#send (blocking) 0.060000 0.030000 0.090000 ( 0.088574) ----------------------------------------------------------- total: 0.760000sec

                                     user     system      total        real

Promise 0.010000 0.000000 0.010000 ( 0.014602) RubyPromise 0.020000 0.010000 0.030000 ( 0.022575) Promise#== 0.010000 0.000000 0.010000 ( 0.015162) RubyPromise#== 0.020000 0.000000 0.020000 ( 0.019323) Promise#object_id 0.010000 0.000000 0.010000 ( 0.015996) RubyPromise#object_id 0.010000 0.000000 0.010000 ( 0.019146) Promise#send 0.010000 0.010000 0.020000 ( 0.015637) RubyPromise#send 0.020000 0.000000 0.020000 ( 0.019562) Promise (blocking) 0.040000 0.020000 0.060000 ( 0.069022) RubyPromise (blocking) 0.050000 0.030000 0.080000 ( 0.080459) Promise#== (blocking) 0.050000 0.030000 0.080000 ( 0.068640) RubyPromise#== (blocking) 0.050000 0.020000 0.070000 ( 0.084409) Promise#object_id (blocking) 0.050000 0.030000 0.080000 ( 0.067952) RubyPromise#object_id (blocking) 0.060000 0.030000 0.090000 ( 0.085177) Promise#send (blocking) 0.040000 0.020000 0.060000 ( 0.067793) RubyPromise#send (blocking) 0.060000 0.030000 0.090000 ( 0.086539)

To run the test suite:

rake

To run the benchmarks:

rake bench