[release/6.0] Enforce scatter/gather file I/O Windows API requirements et. al. #58423
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And use pinned GCHandles and IntPtrs instead of MemoryHandles when passing the segment array to the bottom-most method.
…ddrOfPinnedObject.
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Tagging subscribers to this area: @dotnet/area-system-io Issue DetailsBackport of #57424 to release/6.0 /cc @adamsitnik @teo-tsirpanis Customer ImpactTestingRisk
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I suggest we wait until #58447 is merged, where I will subsequently submit a PR of these changes against the head of this PR's branch. |
What is the risk to the feature itself though? This seems like a significant change to a somewhat complex/perf sensitive area. |
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@dotnet/area-system-io is this backport something you support? we need a call one way or another. I haven't dug into it. |
It is something that we support and want as part of .NET 6, but we need to wait until #58447 is merged. |
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@dotnet/area-system-io If we are still wanting to get this in for 6.0, it'll need to be presented to tactics this week. |
* Allocate an array of memory handles only if needed. * Remove an unnecessary variable in the multiple-syscall write gather. * Actually verify the content read by the read scatter operation. * Delay allocating native memory. * Verify that the whole file was read in the scatter/gather test. * Test the case when the scatter/gather buffers are acceptable by the Windows API. * Avoid null pointer dereferences when passing an empty segment array. * Test performing scatter/gather I/O with an empty segment array. Co-authored-by: Stephen Toub <stoub@microsoft.com>
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@jeffhandley I've cherry-picked the changes from follow-up PR (#58447) and tested it locally. Once the CI is green we can merge it. It's not a release blocker as it's fixing a bug for a feature which very few know that we actually support (NO_BUFFERING). |
Thanks. To confirm, is the fix breaking in any way at all in the edge case usage? |
No, the algorithm falls back to issuing many syscalls for each buffer segment. |
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Failing check is #48717. |
jeffhandley
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Backport of #57424 to release/6.0
/cc @adamsitnik @teo-tsirpanis
Customer Impact
Without this fix, users of
RandomAccess.ReadAsync(IReadOnlyList<Memory<byte>>)andRandomAccess.WriteAsync(IReadOnlyList<ReadOnlyMemory<byte>>)might get an IO exception for a valid input on Windows.Testing
In #57717 (before the ported PR got merged) we have added new tests to extend the NO_BUFFERING tests and cover all scenarios.
In #57424 (what we are backporting here) a unit test that was failing before the fix has been added. It's now passing.
To ensure there is no perf regression new benchmarks have been added to performance repo: dotnet/performance#1967 and run manually on a Windows machine.
Risk
Low, as it's a bug fix for a feature that has been introduced in .NET 6 and has not been widely adopted yet.