From: Trans <transfire@...>
Date: 2008-09-10T08:48:49+09:00
Subject: Re: Drake: Distributed Rake



On Sep 9, 1:54 pm, Trans <transf...@gmail.com> wrote:
> 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".

I thought someone else might notice it and elaborate but there is
another potential benefit of this notation. Eg.

     task :a => [[:x, :y, :z], [:m, :n], :r]

Where :x, :y, :z can be run in parallel, as can :m and :n, but the
groups must run one before the other.

T.