From: Luis Lavena <luislavena@...>
Date: 2011-01-30T11:01:29+09:00
Subject: [ruby-core:34991] Understanding realpath_rec behavior

Hello,

Some developers at RubyInstaller group have been started to dig into
Ruby C code to better under the quantity of API calls performed under
Windows.

Part of this quest, some questions raised in relation to realpath_rec
behavior and how it stat every single directory in a PATH.

For example:

(with cwd been C:\Users\Luis\Projects\oss\oci\rubyinstaller\sandbox)

irb> File.realpath('foo.rb')

Will generate 7 lstat() requests -- in our case winnt_stat -- each one
for a part of the path:

C:/Users
C:/Users/Luis
C:/Users/Projects
C:/Users/Projects/oss
C:/Users/Projects/oss/oci
C:/Users/Projects/oss/oci/rubyinstaller
C:/Users/Projects/oss/oci/rubyinstaller/foo.rb

As I understand the purpose of this:

- It iterates over each individual directory to determine if the
directory exist, and if so, in the case of a link, perform readlink()
on it and resolve it.

- It collects in loopcheck the traversal to avoid recursive lookup
which could only happen in the case of links.

- It triggers ENOENT early as possible.

Windows lacks readlink() functionality, so while even excluding the
readlink() part, still the traversal is performed.

There is also an evaluation of . and .., but all the paths arriving to
realpath_rec has already been expanded.

I've tried "../sandbox/foo.rb" and "./foo.rb" all resulted in the same
quantity of lstat() invocations.

Is all the above correct? I'm missing something in the purpose of realpath_rec?

In case all my observations are correct, I think realpath_rec should
be changed to a platform specific implementation for Windows inside
win32/win32.c that resolves the lookup accordingly to Windows API.

While Windows provides symlink/hardlink and junction points interface,
adapt Ruby codebase to consider those [1] and take advantage of them
would be very extensive modification, not to mention the change in
behavior that will cause to Ruby users on Windows [2].

Please let me know your thoughts, comments and feedback on this so we
can start looking into an alternative mechanism Windows-specific.

Thank you.

[1] http://msdn.microsoft.com/en-us/library/aa365680(VS.85).aspx
[2] http://msdn.microsoft.com/en-us/library/aa365682(v=VS.85).aspx
-- 
Luis Lavena
AREA 17
-
Perfection in design is achieved not when there is nothing more to add,
but rather when there is nothing more to take away.
Antoine de Saint-Exup�ry