From: Ned Konz <ned@...>
Date: 2002-06-28T23:04:16+09:00
Subject: Re: Transparent asynchronous execution

On Friday 28 June 2002 03:38 am, Max Maischein wrote:
> For the implementation, almost everything seems to go smoothly
> except for the delegation part. Before the result becomes
> available, I want the Promise class to block the calling thread on
> every message sent to it (this could maybe done by overriding
> Object#send), and after the result becomes available, I want the
> Promise to send all messages to the result (i.e., I want the
> Promise to be as transparent to the caller as possible). I've
> looked at the Delegator class, but this class wants to know which
> object it delegates to - the Promise dosen't know which object it
> will delegate to until the result becomes available - how can I
> approach this problem ?

Easy: don't make Promises transparent. i.e. require that their user 
send them a particular message (say :value here):

foo = Promise(1,2,3) { |a,b,c|
  r1 = some_function_that_takes_long_to_compute( a,b,c )
  r2 = some_other_function_that_takes_even_longer( r1 )
  r2
} 
bar = a_third_function_that_takes_long_to_compute( 1,2,3 )
print calculate_statistics( bar, foo.value )

This way, Promise.value can be defined as something like:

	def value
		@thread.join	# blocks if thread is not done;
					# thread puts result into @result
		@result
	end

-- 
Ned Konz
http://bike-nomad.com
GPG key ID: BEEA7EFE