Cache Xcode version at the module level

Cache Xcode version at the module level

XcodeVersion may end up being called many times when building large
projects, so cache the version for performance reason. The xcodebuild
command has also been observed to return incorrect values when called
by multiple processes in parallel, so reducing the number of calls
here reduce the risk of encountering this issue.

BUG=408
R=justincohen@chromium.org, thakis@chromium.org

Committed: https://code.google.com/p/gyp/source/detail?r=1854

[sdefresne, 2014-02-18 17:09:27]

+ thakis as asked offline by justincohen

[justincohen, 2014-02-18 17:11:06]

What was xcodeversion returning?  What was the incorrect value?

LGTM

[Nico, 2014-02-18 17:11:57]

Do you have performance numbers on how much this helps? (I thought this used to
be cached on all code paths – is that wrong, or did some recent change regress
gyp performance?)

Do you have a bug link for the concurrent invocation wrongness?

Other than that, lgtm

https://codereview.chromium.org/170773002/diff/1/pylib/gyp/xcode_emulation.py
File pylib/gyp/xcode_emulation.py (right):

https://codereview.chromium.org/170773002/diff/1/pylib/gyp/xcode_emulation.py...
pylib/gyp/xcode_emulation.py:1070: def XcodeVersion():
Huh, is this new? I don't remember there being a global function for this.

[sdefresne, 2014-02-18 17:28:33]

Thank you for the review.

You can find one such broken invocation at in the issue 408
(https://code.google.com/p/gyp/issues/detail?id=408). The output of "xcodebuild
-version" can be seen on the terminal while it should have been written to the
pipe, so something is amiss there (I think xcodebuild really does not like
multiple invocation, and writes on stderr).

For reference, when running "gclient runhooks" for chromium for iOS, I record
more than 1700 calls to XcodeVersion).

https://codereview.chromium.org/170773002/diff/1/pylib/gyp/xcode_emulation.py
File pylib/gyp/xcode_emulation.py (right):

https://codereview.chromium.org/170773002/diff/1/pylib/gyp/xcode_emulation.py...
pylib/gyp/xcode_emulation.py:1070: def XcodeVersion():
On 2014/02/18 17:11:57, Nico (away Feb 11 - Feb 17) wrote:
> Huh, is this new? I don't remember there being a global function for this.

I extracted the function out of the XcodeSettings object and made it a global in
change 1849 (https://code.google.com/p/gyp/source/detail?r=1849) so that I can
call it (indirectly) from CloneConfigurationForDeviceAndEmulator in change 1850
(https://code.google.com/p/gyp/source/detail?r=1850).

This new code path didn't use the cache (since the cache was only enabled when
called through an XCodeSettings object), and this CL move the cache at the
module level so that all calls to XCodeVersion benefits from the cache.

[sdefresne, 2014-02-18 17:29:30]

Committed patchset #1 manually as r1854 (presubmit successful).