Reorganize channels.md: show basics before bounding strategies, add multiple readers/writers example

[Copilot]

The System.Threading.Channels article introduced bounding strategies before covering the producer/consumer APIs, and had no end-to-end example of concurrent multiple producers and consumers.

Changes

• Reordered sections: Producer APIs → Consumer APIs → Common usage patterns now precede Bounding strategies, so readers encounter the operational API before configuration details.
• New section: "Multiple producers and consumers" under Common usage patterns, with a complete example showing 3 concurrent producers and 2 concurrent consumers sharing a single channel.
• New snippet: Program.MultipleReadersWriters.cs — fan-out/fan-in pattern using Task.WhenAll, ReadAllAsync, and a single Writer.Complete() after all producers finish.

Channel<Coordinates> channel = Channel.CreateUnbounded<Coordinates>(
    new UnboundedChannelOptions { SingleWriter = false, SingleReader = false });

Task[] producerTasks = Enumerable.Range(0, 3).Select(id => Task.Run(async () =>
{
    // each producer writes a unique coordinate series
    await channel.Writer.WriteAsync(/* ... */);
})).ToArray();

Task[] consumerTasks = Enumerable.Range(0, 2).Select(_ => Task.Run(async () =>
{
    await foreach (var coordinates in channel.Reader.ReadAllAsync())
        Console.WriteLine(coordinates);
})).ToArray();

await Task.WhenAll(producerTasks);
channel.Writer.Complete();          // signal only after ALL producers are done
await Task.WhenAll(consumerTasks);

Original prompt

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This section details on the original issue you should resolve

<issue_title>Badly organised</issue_title>
<issue_description>### Type of issue

Other (describe below)

Description

You start with bounding strategies before showing the basics of operation. Then you don't show any example of a multiple reader/writer.

Page URL

https://learn.microsoft.com/en-us/dotnet/core/extensions/channels

Content source URL

https://github.com/dotnet/docs/blob/main/docs/core/extensions/channels.md

Document Version Independent Id

73e99a1a-078d-c96b-9d05-7c47acaf7fb4

Article author

@IEvangelist

Metadata

• ID: e9152c35-17b4-bbf2-7ec9-3e867c0a48aa
• Service: dotnet-fundamentals

Related Issues

---

Associated WorkItem - 558445</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Badly organised #44713

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Internal previews

📄 File	🔗 Preview link
docs/core/extensions/channels.md	System.Threading.Channels library

[Copilot]

Pull request overview

This PR updates the System.Threading.Channels documentation to improve learning flow and adds a new end-to-end example demonstrating concurrent multiple producers and consumers sharing a single channel.

Changes:

• Added a new “Basic usage” section with a simple producer/consumer example.
• Added a new “Multiple producers and consumers” section and a corresponding snippet demonstrating fan-out/fan-in over a single channel.
• Updated/normalized several xref links and some wording in the article.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 6 comments.

File	Description
docs/core/extensions/channels.md	Adds “Basic usage”, adds multi-producer/multi-consumer section, and adjusts section structure/xrefs.
docs/core/extensions/snippets/channels/Program.MultipleReadersWriters.cs	New snippet that demonstrates 3 producers and 2 consumers using an unbounded channel with multi-reader/writer options.

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