optimize task creation

[GarrettBeatty]

Stacked PRs:

• Content Language Bug Fix #4224
• use max size semaphore #4220
• ->optimize task creation #4219

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Description

1. Previously we would n number of tasks, where n is the number of parts all at the same time, and each task would then fight for an http slot. This was fine, but in cases where there are lots of parts (e.g. 10,000) this would mean the .net task scheduler would have to create 10,000 tasks and manage them all. Instead, we only create up to concurrentservicerequests tasks at a time. This is done by moving the _httpConcurrencySlots.WaitAsync outside of the task creation and into the for loop that creates the task itself.

2. I also updated the cancellation token logic to use the linked token when applicable. This would apply to scenarios where if one part fails to download we want it to cancel the other linked tokens

Motivation and Context

#3806

Testing

1. Reran all tests and they pass
2. Reran performance tests and they have same performance

Run:1 Secs:1.866644 Gb/s:23.009033
Run:2 Secs:1.363005 Gb/s:31.511007
Run:3 Secs:1.776760 Gb/s:24.173027
Run:4 Secs:0.890440 Gb/s:48.234192
Run:5 Secs:0.946861 Gb/s:45.360061
Run:6 Secs:0.940810 Gb/s:45.651798
Run:7 Secs:0.871014 Gb/s:49.309991
Run:8 Secs:0.882859 Gb/s:48.648384
Run:9 Secs:0.885273 Gb/s:48.515754
Run:10 Secs:0.866490 Gb/s:49.567436

4. reran all integ tests
5. dry run 16f30d8d-ec62-40bb-ab69-5f50383ed393 pass

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

• My code follows the code style of this project
• My change requires a change to the documentation
• I have updated the documentation accordingly
• I have read the README document
• I have added tests to cover my changes
• All new and existing tests passed

License

• I confirm that this pull request can be released under the Apache 2 license

[Copilot]

Pull request overview

This PR optimizes task creation in multipart downloads by limiting concurrent task creation to match the configured HTTP concurrency limit. Previously, all download tasks were created simultaneously and competed for HTTP slots, which could create thousands of tasks for large files. The optimization moves the semaphore acquisition outside of task creation into the main loop, ensuring only ConcurrentServiceRequests tasks exist at any time.

Key Changes:

• Moved _httpConcurrencySlots.WaitAsync from inside CreateDownloadTaskAsync to the task creation loop in StartDownloadsAsync
• Added error handling to release HTTP slots if task creation fails
• Updated comments to reflect the new control flow