From: Stefan Zager <szager@google.com>
Date: Wed, 12 Feb 2014 18:20:12 GMT
Subject: Re: Make the git codebase thread-safe
Message-ID: <CAHOQ7J8QxfvtrS2KdgzUPvkDzJ1Od0CMvdWxrF_bNacVRYOa5Q@mail.gmail.com>
In-Reply-To: <CABPQNSZ_LLg5i+mpwUj7pzXVQMY1tcXz2gJ+PWG-mP1iyjxoaw@mail.gmail.com>

On Wed, Feb 12, 2014 at 3:59 AM, Erik Faye-Lund <kusmabite@gmail.com> wrote:
> On Wed, Feb 12, 2014 at 2:54 AM, Stefan Zager <szager@chromium.org> wrote:
>>
>> We are particularly concerned with the performance of msysgit, and we
>> have already chalked up a significant performance gain by turning on
>> the threading code in pack-objects (which was already enabled for
>> posix platforms, but not on msysgit, owing to the lack of a correct
>> pread implementation).
>
> How did you manage to do this? I'm not aware of any way to implement
> pread on Windows (without going down the insanity-path of wrapping and
> potentially locking inside every IO operation)...

I don't want to steal the thunder of my coworker, who wrote the
implementation.  He plans to submit it upstream soon-ish.  It relies
on using the lpOverlapped argument to ReadFile(), with some additional
tomfoolery to make sure that the implicit position pointer for the
file descriptor doesn't get modified.

Stefan