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Nanaloveyuki
78 lines
2.0 KiB
Markdown
78 lines
2.0 KiB
Markdown
---
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name: async-logger-dropped-count
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group: api
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category: async
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update-time: 20260512
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description: Read the number of records dropped by the async logger because of overflow or queue clearing.
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key-word:
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- async
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- logger
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- queue
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- public
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---
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## Async-logger-dropped-count
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Read the cumulative number of records dropped by an async logger. This metric is useful when overflow policy or forced shutdown behavior may discard queued data.
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### Interface
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```moonbit
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pub fn[S] AsyncLogger::dropped_count(self : AsyncLogger[S]) -> Int {}
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```
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#### input
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- `self : AsyncLogger[S]` - Async logger whose dropped-record counter should be inspected.
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#### output
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- `Int` - Number of records dropped so far.
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### Explanation
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Detailed rules explaining key parameters and behaviors
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- The counter increases when overflow policy discards records.
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- The counter can also increase when `close(clear=true)` or `shutdown(clear=true)` abandons queued records.
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- This is a cumulative counter for the lifetime of the logger value.
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- Use this helper when you need a focused loss metric rather than a full `state()` snapshot.
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### How to Use
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Here are some specific examples provided.
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#### When Need To Detect Loss Under Pressure
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When queue overflow may discard records:
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```moonbit
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if logger.dropped_count() > 0 {
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println("async log loss detected")
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}
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```
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In this example, the code checks whether the async logger has already discarded records.
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#### When Validate Shutdown Behavior In Tests
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When a test intentionally clears the queue:
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```moonbit
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logger.close(clear=true)
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ignore(logger.dropped_count())
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```
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In this example, the drop counter helps confirm that abandoned backlog was tracked.
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### Error Case
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e.g.:
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- If no records have been dropped, the method simply returns `0`.
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- If callers need to know why records were lost, they must interpret this metric together with overflow policy and shutdown behavior.
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### Notes
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1. This helper reports record loss only; it does not explain the full logger state.
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2. Pair it with `pending_count()` or `state()` when investigating backlog pressure.
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