From: Trans <transfire@...>
Date: 2008-09-10T02:54:42+09:00
Subject: Re: Drake: Distributed Rake


On Sep 9, 2:58 am, quixoticsycoph...@gmail.com wrote:
> In a given Rakefile, it is possible (even likely) that the dependency
> tree has not been properly defined.  Consider
>
>    task :a => [:x, :y, :z]
>
> With single-threaded Rake, _x_,_y_,_z_ will be invoked *in that order*
> before _a_ is invoked.  However with drake --threads=N (for N > 1),
> one should not expect any particular order of execution.  Since there
> is no dependency specified between _x_,_y_,_z_ above, Drake is free to
> run them in any order.
>
> If you wish _x_,_y_,_z_ to be invoked sequentially, then write
>
>    task :a => seq[:x, :y, :z]
>
> This is shorthand for
>
>    task :a => :z
>    task :z => :y
>    task :y => :x
>
> Upon invoking _a_, the above rules say: "Can't do _a_ until _z_ is
> complete; can't do _z_ until _y_ is complete; can't do _y_ until _x_
> is complete; therefore do _x_."  In this fashion the sequence
> _x_,_y_,_z_ is enforced.
>
> The problem of insufficient dependencies plagues Makefiles as well.
> Package maintainers affectionately call it "not j-safe."


Hmmm.... this is not backward compatible. Things could go very badly
if I tried -j3 on my "badly" written Rakefiles.

May I make a suggestion? Have

    task :a => [:x, :y, :z]

translate into the task :a => :z => :y => :x thing. And then

    task :a => [[:x, :y, :z]]

Run in parrallel.

That way all old script work fine, and as we get smart and make our
tasks j-safe we can add the extra "j-array".

And besides it sort of looks like parallel marks || x || ;)

Other than this one thing, I say very nice work.

T.