Re: [PATCH] mingw: enable atomic O_APPEND

From: Johannes Sixt <j6t@kdbg.org>
Date: Aug 14, 2018, 18:29 UTC
Message-ID: <313beb50-f5bd-ace6-8d6d-5f2a9e7cb6e7@kdbg.org>
In-Reply-To: <20180813223701.GC16006@sigill.intra.peff.net>

Am 14.08.2018 um 00:37 schrieb Jeff King:

Show 16 quoted lines

> And then you can do something like:
> 
>    for size in 4097 8193 16385 32769 65537 131073 262145 524289 1048577; do
>      >out ;# clean up from last run
>      echo "Trying $size..."
>      timeout 5 ./write $size out
>      if ! ./check $size <out; then
>        echo "$size failed"
>        break
>      fi
>    done
> 
> On my Linux system, each of those seems to write several gigabytes
> without overlapping. I did manage to hit some failing cases, but they
> were never sheared writes, but rather cases where there was an
> incomplete write at the end-of-file.

I used your programs with necessary adjustments (as fork() is not available), and did similar tests with concurrent processes. With packet sizes 1025, 4093, 7531 (just to include some odd number), and 8193 I did not observe any overlapping or short writes.

I'm now very confident that we are on the safe side for our purposes.

-- Hannes