Make all shutdown and force_flush methods async

Changes

@@ -2,6 +2,8 @@ Revision history for OpenTelemetry
 
 {{$NEXT}}
 
+    * Document all shutdown and force_flush methods as async
+
 0.017     2023-11-19 12:39:37+00:00 Europe/London
 
     * Undo conditional logic in Tracer's in_span introduced in 0.016.

lib/OpenTelemetry/Exporter.pod

@@ -8,11 +8,13 @@ OpenTelemetry::Exporter - Abstract interface of an OpenTelemetry exporter
 
     use Object::Pad;
     use OpenTelemetry::SDK::Trace::Span::Processor::Batch;
+    use Future::AsyncAwait;
 
     class My::Exporter :does(OpenTelemetry::Exporter) {
-        method export      ( $spans, $timeout // undef ) { ... }
-        method shutdown    (         $timeout // undef ) { ... }
-        method force_flush (         $timeout // undef ) { ... }
+        method export ( $spans, $timeout // undef ) { ... }
+
+        async method shutdown    ( $timeout // undef ) { ... }
+        async method force_flush ( $timeout // undef ) { ... }
     }
 
     # Use it with a span processor
@@ -51,32 +53,35 @@ L<OpenTelemetry::Constants/Trace Export Results>.
 
 =head2 shutdown
 
-    $result = $exporter->shutdown( $timeout // undef );
+    $result = await $exporter->shutdown( $timeout // undef );
 
-Takes an optional timeout value and returns the outcome of the shutdown
-process. The shutdown process must include the effects of L</force_flush>,
-described below. After shutting down, the exporter is not expected to do any
-further work, and should ignore any subsequent calls.
+Takes an optional timeout value and returns a L<Future> that will be done
+when this exporter has completed shutting down. The shutdown process must
+include the effects of L<force_flush>, described below. After shutting down,
+the exporter is not expected to do any further work, and should ignore any
+subsequent calls.
 
-The return value will be one of the
+The value of the future will be one of the
 L<OpenTelemetry::Constants/Trace Export Results>.
 
 =head2 force_flush
 
-    $result = $exporter->force_flush( $timeout // undef );
+    $result = await $exporter->force_flush( $timeout // undef );
 
-Takes an optional timeout value and returns the outcome of the flushing
-process. Flushing signals to the exporter that it should export the data for
-any unexported spans as soon as possible. This could be due to an imminent
-shutdown, but does not have to be.
+Takes an optional timeout value and returns a L<Future> that will be done
+when this exporter has finished flushing. Flushing signals to the exporter
+that it should export the data for any unprocessed spans as soon as possible.
+This could be due to an imminent shutdown, but does not have to be.
 
-The return value will be one of the
+The value of the future will be one of the
 L<OpenTelemetry::Constants/Trace Export Results>.
 
 =head1 SEE ALSO
 
 =over
 
+=item L<Future>
+
 =item L<OpenTelemetry::Constants>
 
 =item L<OpenTelemetry::Trace::Span::Processor>