[release/6.0-staging] TypeDescriptor threading fixes

[steveharter]

Backport of #96846 and #97236 to release/6.0-staging.

The 8.0 backport is at #101305.

Customer Impact

See issues #92394 and #30024.

There is a threading issue corrupts internal caches, causing various TypeDescriptor methods to return incorrect information. The most likely time it would occur is during warm-up when there are several concurrent threads using various TypeDescriptor static methods.

Technical details

The locking behavior was not correct for multiple threads. Various analysis at:

• Concurrency issue in TypeDescriptor.GetConverter(type) #30024 (comment)
• Concurrency issue in TypeDescriptor.GetConverter(type) #30024 (comment)
• Bugfix/30024 problem with concurrency type descriptor getconverter #85156 (comment)
• TypeDescriptor.GetProperties(object instance) is not thread-safe #92394 (comment)

Regression

No, it appears to have existed in .NET Framework before being ported to .NET Core.

Testing

Previous PR attempts added tests which were ported. Additional tests added for deadlock cases. In addition, the fixes were successfully applied to a .NET Framework local build which was tested by an external customer reporting these issues. It is expected to be ported to .NET framework as well.

The fixes were in v9.0 around 4 months ago with no issues reported.

Risk

Low, as noted there have been no regressions notes in the last 4 months.

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[steveharter]

CI Failures are known, and also occurring with other PRs such as https://github.com/dotnet/runtime/runs/23919179513

System.IO.Net5Compat.Tests.WorkItemExecution
System.IO.Tests.WorkItemExecution

The Helix Work Item failed. Often this is due to a test crash or infrastructure failure. See the Helix Test Logs tab in the Results page of Azure DevOps.

[steveharter]

/ba-g Build Analysis does not show actionable failures; only shows 2 known test errors