[grid] improved the new session handling when the queue is empty

[joerg1985]

Description

This PR implements two strategies to reduce the overhead of the new session runnable:

• peek into the a local queue to avoid collecting stereotypes when the queue is empty.
• ensure all slots share the same stereotype instance to hit the fast-path in .equals

Motivation and Context

A idle selenium server will check the session queue each 10ms, therefore the stereotypes of the slots need to be collected. This will make the idle server not really idle, this can be observed when profiling the GC or looking at the power consumption of an VM. The more cores/threads the system has available, the more slots need to be collected, the more garage is generated.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• I have read the contributing document.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codecov-commenter]

Codecov Report

Patch and project coverage have no change.

Comparison is base (b543555) 57.28% compared to head (fe8de05) 57.28%.

❗ Current head fe8de05 differs from pull request most recent head 3a4b19a. Consider uploading reports for the commit 3a4b19a to get more accurate results

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Additional details and impacted files

@@           Coverage Diff           @@
##            trunk   #12385   +/-   ##
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  Coverage   57.28%   57.28%           
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  Files          86       86           
  Lines        5333     5333           
  Branches      193      193           
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  Hits         3055     3055           
  Misses       2085     2085           
  Partials      193      193           

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[joerg1985]

@diemol this PR will avoid the lookup in a remote queue and still improve the situation with a local queue.
Is this better than in the original #12336 where the queue was always queried?

[diemol]

Yes, this solution is a very good idea. Thank you, @joerg1985!