ReusableUtf8JsonWriter holds on the `IBufferWriter<byte>` after `Return`

[gfoidl]

aspnetcore/src/SignalR/common/Shared/ReusableUtf8JsonWriter.cs

Line 59 in 6a96694

writer._writer.Reset();

With Reset only the internal state is reset, but the output remains the same (cf. code).

So the IBufferWriter<byte> that is set in Rent will be referenced by the (pooled) Utf8JsonWriter, so the lifetime for the IBufferWriter<byte> is bound to the pooled Utf8JsonWriter -- at least until the next Rent when a new one is set. Thus the IBufferWriter<byte> can't be GCed.

In the STJ internal type Utf8JsonWriterCache an internal method is used to reset the output too.

I'm just curios if the extended lifetime is a latent problem or not.

Possible mitigations could be:

• Dispose -- not really, as the instance can't be re-used then
• Reset(Stream.Null) -- solves the lifetime problem, but allocates
• reset by setting to a null-IBufferWriter (type needs to be created)
• ?
• make Utf8JsonWriter.ResetAllStateForCacheReuse public -- but this doesn't play nice with the disposal checks in that type

#9607 introduced the ReusableUtf8JsonWriter.

[BrennanConroy]

I'm just curios if the extended lifetime is a latent problem or not.

I don't think it's an issue, worst case seems to be it'll hold onto a few instances of the underlying writer which could cause the GC to not clean them up.

But it's a nice thing to fix up. Not sure what a good solution is though 😆

• reset by setting to a null-IBufferWriter (type needs to be created)

This seems like it could be ok? Just have a static instance of an empty class (or one that throws if used).