📝 document runtime sink failure counters

2026-07-30 15:04:48 +00:00 · 2026-06-13 23:14:22 +08:00
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+---
+name: runtime-sink-file-rotation-failures
+group: api
+category: runtime
+update-time: 20260613
+description: Read the number of rotation failures recorded by a file-backed RuntimeSink.
+key-word:
+    - runtime
+    - sink
+    - file
+    - public
+---
+
+## Runtime-sink-file-rotation-failures
+
+Read the number of rotation failures recorded by a file-backed `RuntimeSink`. This helper is useful when direct runtime rotation behavior should be observed operationally.
+
+### Interface
+
+```moonbit
+pub fn RuntimeSink::file_rotation_failures(self : RuntimeSink) -> Int {
+```
+
+#### input
+
+- `self : RuntimeSink` - Runtime sink whose rotation-failure counter should be inspected.
+
+#### output
+
+- `Int` - Number of recorded rotation failures.
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- Plain `File` runtime variants report the wrapped `FileSink` rotation-failure count.
+- `QueuedFile` runtime variants forward the metric from the wrapped inner `FileSink`.
+- Non-file runtime variants return `0`.
+- The counter is cumulative until `file_reset_failure_counters()` clears it.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Need Rotation-specific Diagnostics
+
+When support output should reveal whether rotation is failing:
+```moonbit
+let count = sink.file_rotation_failures()
+```
+
+In this example, the runtime sink exposes a focused metric for direct rotation-path health.
+
+#### When Validate Runtime Rotation Tuning
+
+When changed rotation settings should be checked in operation:
+```moonbit
+ignore(sink.file_rotation_failures())
+```
+
+In this example, callers can observe whether runtime rotation changes introduced problems.
+
+### Error Case
+
+e.g.:
+- If the runtime sink is not file-backed, the method returns `0`.
+
+- If callers need both rotation config and failure metrics, they should combine this helper with `file_rotation_config()` or `file_state()`.
+
+### Notes
+
+1. Use this helper when diagnosing direct runtime file rotation reliability.
+
+2. It is especially relevant when runtime rotation policy can change after startup.