From: quixoticsycophant@...
Date: 2008-09-09T19:03:43+09:00
Subject: Re: Drake: Distributed Rake

On Sep 9, 4:52 am, David Masover <ni...@slaphack.com> wrote:
>
> So what do you do with things which aren't thread-save? Or "j-safe"?
>

The same thing you do with a Makefile that isn't j-safe: (1) write the
dependencies correctly, which makes it j-safe, or (2) don't run it
with -j.

> And how is this different than running Rake with 'task' set to an alias
> of 'multitask'?

If 'task' became 'multitask', Rake would run all your tasks at once --
all at the same time.  That's probably not what you want :)

Thinking in terms of parallel execution has a little learning curve.
It's certainly a not a natural transition coming from single-threaded
thinking.

Incidentally there is a good litmus test for determining whether you
get the gist of parallelism: once it becomes obvious that 'multitask'
is a mistake, then you probably get it.  The dependency graph tells us
what can be run in parallel and what can't.  It's a math problem.
'multitask' stomps it all to pieces, having the power to declare 2 + 5
= 8 if it so chooses.

My advice for Rakefile writers is to incrementally move toward -j
correctness.  Start with the bottom tasks first (those executed last)
and work your way up, testing each new task subtree.

Regards,
J