Reduce synchronization lock contention in common code paths

[alzimmermsft]

Description

Prototype PR aiming to reduce synchronization and lock contention in common code paths.

new URL(String) requires a lookup to get the URLStreamHandler for the URL. This lookup uses a HashTable which has synchronized applied to its APIs. In highly threaded environments this can result in drastic contention. There is a similar API new URL(URL, String) which takes an existing URL and copies information from that to the new URL being parsed. If the existing URL already has a URLStreamHandler it circumvents the lookup. Prototype here is using a simple URL that only contains values that will be overridden by the new URL (host).

Collator.getInstance(Locale.ROOT) can result in a Collator instance that synchronized its compare method. This PR modifies the usage to be a ThreadLocal so there isn't contention when using the instance as it'll be local to the calling Thread. Additional investigation should be done if String.compareTo and String.CASE_INSENSITIVE_ORDER could be used instead of a ThreadLocal as those don't synchronized and don't require Thread-based variables.

All SDK Contribution checklist:

• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.

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• Title of the pull request is clear and informative.
• There are a small number of commits, each of which have an informative message. This means that previously merged commits do not appear in the history of the PR. For more information on cleaning up the commits in your PR, see this page.

Testing Guidelines

• Pull request includes test coverage for the included changes.

[azure-sdk]

API change check

API changes are not detected in this pull request.

[alzimmermsft]

/azp run java - core

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