gRPC .NET C# server request handling

[Martin Scholz]

Is there any documentation how gRPC on server side with .NET or C# is handling multiple request under the hood. Does every request consume a thread until it's finished. Or can another request use the this thread when it is asnyc? And what it is the number of concurrent requests/threads.

[Christopher Warrington - MSFT]

On Wednesday, March 11, 2020 at 1:30:57 PM UTC-7, Martin Scholz wrote:
 
> Is there any documentation how gRPC on server side with .NET or C# is
> handling multiple request under the hood.

The closest that I know of is the GrpcEnvironment API documentation [1].

> Does every request consume a thread until it's finished. Or can another
> request use the this thread when it is asnyc?

gRPC C# uses its own thread-pool [2] to handle gRPC operations like reading
from and writing to the network, monitoring for timeouts, and cancelling
requests. After it has figured out which user code to invoke, by default, it
uses the .NET thread pool to run that code. The guards against buggy/slow
user code blocking gRPC from making forward progress.

> And what it is the number of concurrent requests/threads.

Unless customized by calling one of the methods on GrpcEnvironment [3], the
larger of 4 and Environment.ProcessorCount / 2 threads are used to poll 4
completion queues. (A completion queue is the underlying data structure that
gRPC uses to manage its operations.)

[1]: https://grpc.github.io/grpc/csharp/api/Grpc.Core.GrpcEnvironment.html
[2]: https://github.com/grpc/grpc/blob/c1349090872753dcafbb03789bb3417f6d4b2849/src/csharp/Grpc.Core/Internal/GrpcThreadPool.cs
[3]: https://github.com/grpc/grpc/blob/c1349090872753dcafbb03789bb3417f6d4b2849/src/csharp/Grpc.Core/GrpcEnvironment.cs#L198-L249

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Christopher Warrington
Microsoft Corp.

[Martin Scholz]

Thx for the explanation. But wWhat about having 1000 or 10000 bi-directional client streams on the server which may have long waiting async calls to the backend. Is there a need to customize the thread size?

[Jan Tattermusch]

No need to use more threads. The threads will be shared by multiple requests just fine (same idea as with any other thread pool).

If you have a high number of concurrent class (thousands), you might need to adjust the number of allowed concurrent calls on the server though: https://github.com/grpc/grpc/blob/7be8cef10a4ea02b682a44c92f54a645bb9a61d8/src/csharp/Grpc.Core/Server.cs#L125

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Jan Tattermusch

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