Ramsay Jones <ramsay@xxxxxxxxxxxxxxxxxxx> writes:
> 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.
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