[Rake-devel] timestamp checking is slow?

Ittay Dror ittay.dror at gmail.com
Wed Jul 23 05:31:14 EDT 2008

I applied your change and it sped up the execution by 0.1s :-(.

I then just added a 'return Rake::EARLY' at the start of #timestamp. 
This also didn't improve time. So it must be something with the rake 
code that calls the timestamp method.


Mark Watson wrote:
> I ran into a similar issue, the way i got around it was by caching the
> timestamp the first time File.mtime is called.  This brings about its
> own problems because you don't necessarily know that the file won't be
> modified outside the file task.  If you have a task that generates
> several files the cached timestamps won't be updated.
> I tried using Windows API directly instead of File.mtime but this
> wasn't much faster.  I didn't get a chance to look into what make is
> doing, but i suspect it is caching the timestamps too.  Make does
> allow you to specify several files as the output of one task, possibly
> as a way around the problems with caching the timestamp.
> # File task with timestamp speedup.  The regular file task will query
> # the File.mtime for every task that depends on this file.  Typically
> # when compiling c/c++ some header files are included very often, and
> # if a a regular file task is used to represent header files then the
> # File.mtime function will be called each time a source file depends
> # on the header.  By caching the timestamp we insure that this
> # operation occurs only once for each header file.  On typical c/c++
> # projects where most files depend on a core set of headers, a ~3x
> # speedup on rake startup time can be expected with this patch.
> #
> # WARNING: Caching the timestamp may cause problems if the file is
> # generated/updated by another task as a side effect.
> #
> class Rake::FastFileTask < Rake::FileTask
>   # Time stamp for file task.
>   def timestamp
>     # Cache the timestamp since it is accessed often
>     if instance_variable_defined?(:@timestamp)
>       @timestamp
>     else
>       # exist? and mtime can be done together with one call to File.stat, but
>       # for some reason this takes longer on Windows.  Ruby is probably making
>       # several Win32 calls.  Opimization would be to call GetFileAttributesEx()
>       # directly.  Using Win32API module this is slightly faster, making the
>       # call via a c extension would probably be faster again.
>       if File.exist?(name)
>         @timestamp = File.mtime(name.to_s)
>         # Update the time stamp when the task is executed
>         enhance do
>           @timestamp = Time.now
>         end
>         @timestamp
>       else
>         # Build me!
>         Rake::EARLY
>       end
>     end
>   end
> end
> 2008/7/22 Ittay Dror <ittay.dror at gmail.com>:
>> Hi,
>> I'm using Rake (actually Buildr) to compile C++ files. As part of that I'm
>> loading dependencies on header files. The total amount of  dependencies is
>> 869 on 142 obj files.
>> The issue I'm seeing is that it takes a lot of time for Rake to timestamp
>> these files to reach a conclusion that it has nothing to do. Compared to
>> make that takes 0.7 seconds to run, Rake takes 3 seconds. If I remove the
>> creation of the dependencies (but still leave the loading and parsing of the
>> files) rake takes 1 second.
>> I understand that 2 seconds seem like not a long time, but the project I'm
>> working on has over 1000 of source files, so I expect the time to be much
>> larger. Do you think anything can be done to make Rake closer to make? note
>> that without the timestamp checking, the rest of the work doesn't amount to
>> a lot of overhead, so I am hoping it is not the dynamic nature of Ruby that
>> is the cause of the problem (but maybe poor implementation of
>> File(file).mtime?)
>> Thank you,
>> Ittay
>> --
>> --
>> Ittay Dror <ittay.dror at gmail.com>
>> _______________________________________________
>> Rake-devel mailing list
>> Rake-devel at rubyforge.org
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Ittay Dror <ittay.dror at gmail.com>

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