[6.0] Make thread pool thread timeouts configurable

[kouvel]

• Port of Make thread pool thread timeouts configurable #92985 to 7.0 with some changes to accommodate differences in the thread pool implementations. This version covers both the native and managed thread pools, including the native IOCP thread pool.
• This is a more direct port of the port to 7.0: [7.0] Make thread pool thread timeouts configurable #92987
• Added two config options, one that configures the worker and wait thread timeouts, and another that enables keeping some number of worker threads alive after they are created
• This enables services that take periodic traffic to keep some worker threads around for better latency, while allowing extra threads to time out as appropriate for the service

Customer Impact

These config capabilities were requested by a 1p customer for a scenario where a service takes work in waves and is experiencing noticeably high latency with thread pool worker and IOCP threads being torn down and recreated between waves. The config vars enable the service to keep some number of threads always alive, and to increase the timeout for any extra threads that are created. The service is currently using .NET 6.

Regression?

No

Testing

Verified the default behavior hasn't changed when not configured, and verified using events that the config values are working as expected.

Risk

Low. The change is a bit larger in .NET 7 and .NET 6 because it also covers the native worker and IOCP thread pools. The mechanism for configuring is slightly different to allow both the native and managed thread pools to use the same config vars, though similar to before / other config vars.

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Issue Details

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• Port of Make thread pool thread timeouts configurable #92985 to 7.0 with some changes to accommodate differences in the thread pool implementations. This version covers both the native and managed thread pools, including the native IOCP thread pool.
• This is a more direct port of the port to 7.0: [7.0] Make thread pool thread timeouts configurable #92987
• Added two config options, one that configures the worker and wait thread timeouts, and another that enables keeping some number of worker threads alive after they are created
• This enables services that take periodic traffic to keep some worker threads around for better latency, while allowing extra threads to time out as appropriate for the service

Customer Impact

These config capabilities were requested by a 1p customer for a scenario where a service takes work in waves and is experiencing noticeably high latency with thread pool worker and IOCP threads being torn down and recreated between waves. The config vars enable the service to keep some number of threads always alive, and to increase the timeout for any extra threads that are created. The service is currently using .NET 6.

Regression?

No

Testing

Verified the default behavior hasn't changed when not configured, and verified using events that the config values are working as expected.

Risk

Low. The change is a bit larger in .NET 7 and .NET 6 because it also covers the native worker and IOCP thread pools. The mechanism for configuring is slightly different to allow both the native and managed thread pools to use the same config vars, though similar to before / other config vars.

Author:	kouvel
Assignees:	kouvel
Labels:	area-System.Threading
Milestone:	6.0.x

[jeffschwMSFT]

approved. we will take for consideration in 6.0.x

[kouvel]

The remaining failures appear to be known issues unrelated to this change.