📝 document runtime sink state surface

2026-07-24 00:42:18 +00:00 · 2026-06-13 22:38:14 +08:00
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+---
+name: runtime-sink-pending-count
+group: api
+category: runtime
+update-time: 20260613
+description: Read the current queued backlog count from a RuntimeSink.
+key-word:
+    - runtime
+    - sink
+    - queue
+    - public
+---
+
+## Runtime-sink-pending-count
+
+Read the current queued backlog count from a `RuntimeSink`. This is the direct sink-level queue metric behind configured logger pending-count behavior.
+
+### Interface
+
+```moonbit
+pub fn RuntimeSink::pending_count(self : RuntimeSink) -> Int {
+```
+
+#### input
+
+- `self : RuntimeSink` - Runtime sink whose current queue backlog should be inspected.
+
+#### output
+
+- `Int` - Current number of pending queued records.
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- Queue-wrapped runtime variants forward to the wrapped queue sink's `pending_count()` value.
+- Plain console and plain file runtime variants return `0` because they do not own a pending queue here.
+- This is a point-in-time metric and may change immediately after it is read.
+- This method is the direct sink-level API used by `ConfiguredLogger::pending_count(...)`.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Need Direct Queue Backlog Visibility
+
+When code is working with a `RuntimeSink` value directly and wants queue pressure information:
+```moonbit
+let pending = sink.pending_count()
+```
+
+In this example, backlog is read from the runtime sink without going through a logger wrapper.
+
+#### When Verify Manual Drain Progress
+
+When drain loops should observe remaining queue backlog directly:
+```moonbit
+ignore(sink.drain(max_items=8))
+ignore(sink.pending_count())
+```
+
+In this example, the metric helps confirm whether manual queue draining reduced backlog.
+
+### Error Case
+
+e.g.:
+- If the runtime sink is not queue-backed, the method simply returns `0`.
+
+- If callers need the higher-level logger wrapper API, use `ConfiguredLogger::pending_count()` instead.
+
+### Notes
+
+1. Use this helper for simple direct queue visibility on `RuntimeSink` values.
+
+2. Pair it with `dropped_count()` when investigating queue pressure and loss.