📝 document runtime sink failure counters

2026-07-29 14:06:34 +00:00 · 2026-06-13 23:14:22 +08:00
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+---
+name: runtime-sink-file-flush-failures
+group: api
+category: runtime
+update-time: 20260613
+description: Read the number of flush failures recorded by a file-backed RuntimeSink.
+key-word:
+    - runtime
+    - sink
+    - file
+    - public
+---
+
+## Runtime-sink-file-flush-failures
+
+Read the number of flush failures recorded by a file-backed `RuntimeSink`. This helper is useful for direct runtime diagnostics around durability-path problems.
+
+### Interface
+
+```moonbit
+pub fn RuntimeSink::file_flush_failures(self : RuntimeSink) -> Int {
+```
+
+#### input
+
+- `self : RuntimeSink` - Runtime sink whose flush-failure counter should be inspected.
+
+#### output
+
+- `Int` - Number of recorded flush failures.
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- Plain `File` runtime variants report the wrapped `FileSink` flush-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 Durability-path Diagnostics
+
+When support output should show flush-path instability:
+```moonbit
+let count = sink.file_flush_failures()
+```
+
+In this example, the runtime sink exposes whether file flush attempts have been failing.
+
+#### When Inspect Effects Of Auto-flush Policy
+
+When runtime durability tuning should be inspected operationally:
+```moonbit
+ignore(sink.file_flush_failures())
+```
+
+In this example, callers can correlate flush failures with direct runtime file policy choices.
+
+### Error Case
+
+e.g.:
+- If the runtime sink is not file-backed, the method returns `0`.
+
+- If callers need current policy and counters together, `file_state()` is the better API.
+
+### Notes
+
+1. Use this helper when direct runtime flush-path reliability matters.
+
+2. Pair it with `file_auto_flush()` and `file_flush()` when diagnosing durability behavior.