Re: [PATCH v2] Add a Windows-specific fallback to getenv("HOME");

[Karsten Blees <karsten.blees@gmail.com>]

Am 05.06.2014 15:39, schrieb Johannes Schindelin:
> And in particular with your changes to Unicodify the complete environment,
> I am *highly* doubtful that child processes will be able to handle
> themselves properly, unless we spend a whole lot of time converting back
> and forth the environment when calling children.

The unicode version _does_ convert back and forth, in mingw_startup and make_environment_block, respectively. However, as the unicode environment is sorted, this is actually much faster than the original version.

To put things in perspective *:

entire mingw_startup: ~450 µs
 * _wgetmainargs: 25 µs
 * allocate+convert args and environment: 25 µs
 * qsort environment: 15 µs
 * winansi_init: 393 µs

entire mingw_spawnve_fd: ~1250 µs
 * make_environment_block: 25 µs
 * CreateProcessW: 690 µs

Now, the unicode mingw_getenv is O(log n) (~0.15 µs per call) and MSVCRT's getenv is O(n) (~3.6 µs per call).

A git command that just launches a script (e.g. git gui) calls getenv ~25 times. (3.6 µs - 0.15 µs) * 25 = 86 µs, i.e. this compensates the additional startup time (including qsort) more than twice.

(*) Measurements done via QueryPerformanceCounter, with 75 environment entries, on a Core i7 960, Windows 7 x64

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