Exporter::force_flush() interface missing for Logs

[lalitb]

The logs specification requires that the exporter implements force_flush as described here: - https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/logs/sdk.md#forceflush-2. This function can be asynchronous, but if so, the exporter should offer a way to inform the provider of its status.

Apart from that, the force_flush() interface are different for traces and metrics:

Traces:

opentelemetry-rust/opentelemetry-sdk/src/export/trace.rs

Line 63 in a5e2061

fn force_flush(&mut self) -> BoxFuture<'static, ExportResult> {

Metrics:

opentelemetry-rust/opentelemetry-sdk/src/metrics/exporter.rs

Line 24 in a5e2061

async fn force_flush(&self) -> MetricResult<()>;

Looking closer, both interfaces are indeed asynchronous. For traces, the interface returns a Future, making it naturally async, while for metrics, it’s defined using async fn. Although the difference isn’t major, the async fn approach in metrics does look cleaner, more straightforward interface.

[lalitb]

As discussed with @ThomsonTan, the BatchLogProcessor::force_flush should:

• Clear the current batch queue by exporting all logs in it (i.e., calling exporter::export).
• Then, call exporter::force_flush() on the exporter.

The OTLP exporters don’t batch logs; they ensure logs are exported before the export() method returns, so their force_flush can remain empty.