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https://issues.apache.org/jira/browse/ARROW-4717?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16800385#comment-16800385
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Jorgen Thelin commented on ARROW-4717:
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I took a quick look at this, and mostly it is just a straight-forward
s/Task/ValueTask/
However, the biggest impediment to making this change be most impactful is that
a "Span-friendly" overload for the C# *System.IO.Stream.WriteAsync* method --
which directly handles ReadOnlyMemory<T> (without requiring any copying to
intermediate byte[] buffer) and returns ValueTask (no heap alloc) -- is only
available in *.NET Core 2.1* and later.
[Stream.WriteAsync(ReadOnlyMemory<Byte>,
CancellationToken)|https://docs.microsoft.com/en-us/dotnet/api/system.io.stream.writeasync?view=netcore-2.1#System_IO_Stream_WriteAsync_System_ReadOnlyMemory_System_Byte__System_Threading_CancellationToken_]
Currently the C# Apache.Arrow library here is built for both .NET Core 2.1 and
.NET Standard 1.3.
How important is it to maintain compatibility with .NET Standard 1.3?
The *ArrowStreamWriter.WriteBufferAsync* function is directly on the hot-path
for all writes, so switching to using zero-copy memory buffers and zero return
object heap allocation (which needs .NET Core 2.1+) should make a big
performance improvement.
Thoughts?
> [C#] Consider exposing ValueTask instead of Task
> ------------------------------------------------
>
> Key: ARROW-4717
> URL: https://issues.apache.org/jira/browse/ARROW-4717
> Project: Apache Arrow
> Issue Type: Improvement
> Components: C#
> Reporter: Eric Erhardt
> Priority: Major
>
> See [https://github.com/apache/arrow/pull/3736#pullrequestreview-207169204]
> for the discussion and
> [https://devblogs.microsoft.com/dotnet/understanding-the-whys-whats-and-whens-of-valuetask/]
> for the reasoning.
> Using `Task<T>` in public API requires that a new Task instance be allocated
> on every call. When returning synchronously, using ValueTask will allow the
> method to not allocate.
> In order to do this, we will need to take a new dependency on
> {{System.Threading.Tasks.Extensions}} NuGet package.
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