dataconnect(change): add exponential backoff in realtime query subscriptions upon disconnecting from the server

[dconeybe]

Introduce exponential backoff retry strategy for Data Connect realtime query subscriptions when they disconnect or fail to connect. When connection failures occur, the client backs off progressively before retrying, but resets the delay on successful messages, immediate retry triggers, or when a new subscription is registered.

Highlights

• Exponential Backoff Strategy: Replaced the previous fixed 1-second retry delay with an exponential backoff calculator (RetryBackoffCalculator) capped at 10 minutes (600,000ms), using a multiplier of 1.75.
• Subscription Wakeup: Configured new query subscriptions to trigger an immediate retry and reset the backoff calculation, avoiding unnecessary waiting when a user actively requests new data.
• ConflatedSignal Reset Capability: Added a clear() method to ConflatedSignal to allow discarding pending signals, which is utilized to manage retry and wakeup events cleanly.
• Comprehensive Testing: Added unit tests validating retry intervals, backoff scaling, signal clearing, and the immediate wakeup behavior when new subscribers join.

Changelog

• CHANGELOG.md
  • Added a changelog entry noting that realtime query subscriptions now retry connecting using an exponential backoff strategy.
• RetryBackoffCalculator.kt
  • Introduced a new internal thread-safe class to calculate backoff retry delays starting at 1000ms with a 1.75 multiplier and capped at 600,000ms.
• ConflatedSignal.kt
  • Added a clear() method to discard any pending signals, causing subsequent calls to await to suspend until a new signal is emitted.
• DataConnectBidiConnectStream.kt
  • Replaced the hardcoded 1-second retry delay with the new RetryBackoffCalculator and a ConflatedSignal event to handle retries and immediate wakeup actions.
  • Resets the backoff upon new subscriptions or successful message streams.
  • Added testing callback registration methods to allow validation of backoff timings.
• RetryBackoffCalculatorUnitTest.kt
  • Added unit tests verifying RetryBackoffCalculator next value progression, max value ceiling, reset functionality, and thread-safety under concurrent access.
• ConflatedSignalUnitTest.kt
  • Added unit tests verifying the correctness of the new clear() method.
• QuerySubscriptionImplUnitTest.kt
  • Added unit tests verifying that new subscriptions reset backoff, that initial and subsequent connection failures follow the expected retry delays, and that healthy/immediate retries reset backoff state.

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[dconeybe]

/gemini review

[gemini-code-assist]

Code Review

This pull request implements an exponential backoff strategy for retrying realtime query subscription connections. It introduces a thread-safe RetryBackoffCalculator class to compute backoff durations starting at 1000ms with a 1.75 multiplier up to a maximum of 600,000ms. It also adds a clear() method to ConflatedSignal to discard pending signals, and updates DataConnectBidiConnectStream to utilize these components. Comprehensive unit tests have been added to verify the backoff calculation, signal clearing, and overall retry behaviors under various scenarios. I have no feedback to provide as there are no review comments.

[github-actions]

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