[browser] WS & HTTP clients more async

[pavelsavara]

Motivation

I would like to make dispatch of async JSImport onto different thread automatic inside of the JSImport internals.
Draft here

It will have similar effect for the WS+HTTP clients like this change.
So I'm making the necessary changes ahead of time here.

Changes

• stop passing null as synchronous singnal in the MT implementation of WS
• use async SynchronizationContext.Post instead Send where the underlying method is async
• fix unit tests

[ghost]

Tagging subscribers to 'arch-wasm': @lewing
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Issue Details

---

Motivation

I would like to make dispatch of async JSImport onto different thread automatical inside of the JSImport internals.
It will have similar effect for the WS+HTTP client like this change.
So I'm making the necessary changes ahead of time here.

Changes

• stop passing null as synchronous singnal in the MT implementation of WS
• use async SynchronizationContext.Post instead Send where the underlying method is async
• fix unit tests

Author:	pavelsavara
Assignees:	pavelsavara
Labels:	arch-wasm, area-System.Runtime.InteropServices.JavaScript, os-browser
Milestone:	9.0.0

[pavelsavara]

/azp run runtime-wasm

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[pavelsavara]

/azp run runtime-wasm

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[pavelsavara]

/azp run runtime-wasm

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[pavelsavara]

Unrelated MT failure: Log

[15:37:59] info: [2023-12-02T15:37:59.922Z] [FAIL] System.Text.Json.Serialization.Tests.ReferenceHandlerTestsDynamic_AsyncStreamWithSmallBuffer.TestJsonPathDoesNotFailOnMultiThreads
[15:37:59] info: Assert.Throws() Failure: Exception type was not an exact match
[15:37:59] info: Expected: typeof(System.Text.Json.JsonException)
[15:37:59] info: Actual: typeof(System.ArgumentException)
[15:37:59] info: ---- System.ArgumentException : An item with the same key has already been added.
[15:37:59] info: at System.Text.Json.Serialization.Tests.ReferenceHandlerTests.TestIdTask()
[15:37:59] info: at System.Text.Json.Serialization.Tests.ReferenceHandlerTests.TestJsonPathDoesNotFailOnMultiThreads()
[15:37:59] info: --- End of stack trace from previous location ---
[15:37:59] info: ----- Inner Stack Trace -----
[15:37:59] info: at System.Runtime.CompilerServices.ConditionalWeakTable`2[[System.Text.Json.JsonSerializerOptions, System.Text.Json, Version=9.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51],[System.Text.Json.JsonSerializerOptions, System.Text.Json, Version=9.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51]].Add(JsonSerializerOptions key, JsonSerializerOptions value)
[15:37:59] info: at System.Text.Json.Serialization.Tests.JsonSerializerWrapper.JsonSerializerOptionsSmallBufferMapper.ResolveOptionsInstanceWithSmallBuffer(JsonSerializerOptions options)
[15:37:59] info: at System.Text.Json.Serialization.Tests.JsonSerializerWrapper.AsyncStreamSerializerWrapper.ResolveOptionsInstance(JsonSerializerOptions options)
[15:37:59] info: at System.Text.Json.Serialization.Tests.JsonSerializerWrapper.AsyncStreamSerializerWrapper.<DeserializeWrapper>d__16`1[[System.Text.Json.Serialization.Tests.ReferenceHandlerTests.Employee, System.Text.Json.Tests, Version=9.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51]].MoveNext()
[15:37:59] info: at System.Text.Json.Serialization.Tests.StreamingJsonSerializerWrapper.<DeserializeWrapper>d__20`1[[System.Text.Json.Serialization.Tests.ReferenceHandlerTests.Employee, System.Text.Json.Tests, Version=9.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51]].MoveNext()
[15:37:59] info: at System.Text.Json.Serialization.Tests.ReferenceHandlerTests.<TestIdTask>b__65_0()