---
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.