Re: What's cooking in git.git (Apr 2014, #03; Fri, 11)

From: Junio C Hamano <gitster@pobox.com>
Date: Apr 15, 2014, 16:45 UTC
Message-ID: <xmqqeh0ylext.fsf@gitster.dls.corp.google.com>
In-Reply-To: <534985F3.6060501@ramsay1.demon.co.uk>

Ramsay Jones <ramsay@ramsay1.demon.co.uk> writes:

Show 14 quoted lines

> On 11/04/14 23:22, Junio C Hamano wrote:
> [...]
>> [New Topics]
>> 
>> * nd/index-pack-one-fd-per-thread (2014-04-09) 1 commit
>>  - index-pack: work around thread-unsafe pread()
>> 
>>  Enable threaded index-pack on platforms without thread-unsafe
>>  pread() emulation.
>> 
>>  Will merge to 'next' and keep it there for the remainder of the cycle.
>
> The commit message for commit 512ebe5d ("index-pack: work around
> thread-unsafe pread()", 25-03-2014) is a little misleading.

OK.  Can we have a concrete alternative?

    Multi-threaing of index-pack was disabled with c0f8654
    (index-pack: Disable threading on cygwin - 2012-06-26), because
    pread() implementations for Cygwin and MSYS were not thread
    safe.  Recent Cygwin does offer usable pread() and we enabled
    multi-threading with 103d530f (Cygwin 1.7 has thread-safe pread,
    2013-07-19).

    Work around this problem on platforms with a thread-unsafe
    pread() emulation by opening one file handle per thread; it
    would prevent parallel pread() on different file handles from
    stepping on each other.

    Also remove NO_THREAD_SAFE_PREAD that was introduced in c0f8654
    because it's no longer used anywhere.

    This workaround is unconditional, even for platforms with
    thread-safe pread() because the overhead is small (a couple file
    handles more) and not worth fragmenting the code.