On Windows each AIO request seeked a _dup of the descriptor and then read
or wrote through it. A duplicated descriptor shares the file position, and
the seek and the transfer are separate calls, so two threads submitting
requests on one descriptor could transfer at each other's offset. Each
request is now a single ReadFile/WriteFile with an OVERLAPPED offset on
the OS handle, as pread and pwrite already do in Stdio.cpp.
GuestAio reads four distinct blocks of one descriptor from four threads
and checks every result.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HeC9bA3n74TzJRYv9AgBE8
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