📝 document runtime sink file flush methods

2026-07-27 18:32:20 +00:00 · 2026-06-13 23:11:39 +08:00
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+---
+name: runtime-sink-file-flush
+group: api
+category: runtime
+update-time: 20260613
+description: Flush the file sink behind a RuntimeSink when one is present.
+key-word:
+    - runtime
+    - sink
+    - file
+    - public
+---
+
+## Runtime-sink-file-flush
+
+Flush the file sink behind a `RuntimeSink`. This helper is the direct file-specific runtime flush surface for code that owns a sink value instead of a `ConfiguredLogger`.
+
+### Interface
+
+```moonbit
+pub fn RuntimeSink::file_flush(self : RuntimeSink) -> Bool {
+```
+
+#### input
+
+- `self : RuntimeSink` - Runtime sink whose file sink should be flushed.
+
+#### output
+
+- `Bool` - Whether the underlying file flush succeeded.
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- Plain `File` runtime variants forward directly to `FileSink::flush()`.
+- `QueuedFile` runtime variants first attempt `sink.flush()` on the queue wrapper, then call `sink.sink.flush()` on the wrapped file sink.
+- For `QueuedFile`, the queue flush result is ignored and the returned `Bool` comes from the inner file flush.
+- Non-file runtime variants return `false`.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Need Explicit Direct File Durability Steps
+
+When code holds a file-backed `RuntimeSink` directly and should flush it explicitly:
+```moonbit
+ignore(sink.file_flush())
+```
+
+In this example, the runtime sink attempts to flush its file-backed output directly.
+
+#### When Need A File-specific Success Flag
+
+When code should branch on the outcome of a direct file flush:
+```moonbit
+let ok = sink.file_flush()
+```
+
+In this example, callers can distinguish file flush success from a non-file sink shape.
+
+### Error Case
+
+e.g.:
+- If the runtime sink is not file-backed, the method returns `false`.
+
+- If callers want generic queue or sink advancement instead of file-specific behavior, `flush()` is the broader API.
+
+### Notes
+
+1. Prefer this helper when direct runtime code specifically cares about file flush behavior.
+
+2. Queued file sinks may perform both queue flush work and file flush work here.