On 19 May 2010, at 14:13, Heath Kehoe wrote:
> Hello all,
>
> I have recently implemented a build system based on Rake for a decently-sized
> project (~8000 source files) which builds code and data for several libraries
> and applications targeting four separate platforms.
>
> I was new to both rake and ruby when I started; and it's a testament to the
> awesomeness of both that I was able to learn them quickly to be able to
> implement a fairly complicated system in less than a month.
>
> Anyway, I wanted to pass along some comments.
>
> Firstly, when I first got stuff building with rake (replacing a build
> environment that used gnu make) I noticed that a null build (where everything
> was up to date) took a really long time. I used the ruby profiler and found
> that approx. half the run time was spent doing file stats (exist? and mtime),
> with an average of 70 calls *per file* during a rake run. As it runs under
> Cygwin on Windows those file stat operations are more expensive than they are
> on Linux. I should note that I'm using ruby 1.8.7 and the rake that gem
> installed (0.8.7).
Yeah, this is a problem for ruby on windows generally, and somewhat hard to
overcome in the generic case.
> If you look at the FileTask code, the needed? method calls File.exist? then
> timestamp, which calls File.exist? then File.mtime. That's three stats in a
> row right there for the file itself; then each prerequisite is asked for its
> timestamp which generates two stats for each (for FileTasks that is). My
> approach was to create a simple global cache that uses the filename as the
> key and stores the file's mtime.
> Now, I'm not saying rake should adopt this specific optimization; however I
> think you should consider some type of caching to reduce the quantity of
> exist?/mtime calls. Perhaps the FileTask could simply cache its own
> exist?/mtime results (invalidated when execute runs).
It's a bit hacky and incomplete, but here's an intro implementation...
class FileTask < Task
NOFILESTAT = File::Stat.allocate
class << NOFILESTAT
def mtime
Rake::EARLY
end
# TODO fixup other methods that are busted by the fact we had to hack
# with allocate.
end
# Is this file task needed? Yes if it doesn't exist, or if its time stamp
# is out of date.
def needed?
stat == NOFILESTAT || out_of_date?(timestamp)
end
# Time stamp for file task.
def timestamp
stat.mtime
end
def execute(*a)
super.tap { @stat = nil }
end
private
def stat(refresh = false)
return @stat if @stat && !refresh
@stat = begin
File.stat(name)
rescue Errno::ENOENT
NOFILESTAT
end
end
...
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