adding PushMetricExporterInterface (#1097)

open-telemetry/opentelemetry-specification#3563 clarifies the behaviour of
forceFlush with push/non-push metric exporters.
Break forceFlush out into a PushMetricExporterInterface, and update ExportingReader to only collect/flush
if exporter is a push metric exporter.

Metrics/MetricExporter/ConsoleMetricsExporter.php → Metrics/MetricExporter/ConsoleMetricExporter.php

@@ -7,15 +7,15 @@
 use OpenTelemetry\SDK\Common\Instrumentation\InstrumentationScopeInterface;
 use OpenTelemetry\SDK\Metrics\Data\Metric;
 use OpenTelemetry\SDK\Metrics\Data\Temporality;
-use OpenTelemetry\SDK\Metrics\MetricExporterInterface;
 use OpenTelemetry\SDK\Metrics\MetricMetadataInterface;
+use OpenTelemetry\SDK\Metrics\PushMetricExporterInterface;
 use OpenTelemetry\SDK\Resource\ResourceInfo;
 
 /**
  * Console metrics exporter.
  * Note that the output is human-readable JSON, not compatible with OTLP.
  */
-class ConsoleMetricsExporter implements MetricExporterInterface
+class ConsoleMetricExporter implements PushMetricExporterInterface
 {
     /**
      * @var string|Temporality|null

Metrics/MetricExporter/ConsoleMetricExporterFactory.php

@@ -11,6 +11,6 @@ class ConsoleMetricExporterFactory implements MetricExporterFactoryInterface
 {
     public function create(): MetricExporterInterface
     {
-        return new ConsoleMetricsExporter();
+        return new ConsoleMetricExporter();
     }
 }

Metrics/MetricExporter/InMemoryExporter.php

@@ -74,9 +74,4 @@ public function shutdown(): bool
 
         return true;
     }
-
-    public function forceFlush(): bool
-    {
-        return !$this->closed;
-    }
 }

Metrics/MetricExporter/NoopMetricExporter.php

@@ -30,9 +30,4 @@ public function shutdown(): bool
     {
         return true;
     }
-
-    public function forceFlush(): bool
-    {
-        return true;
-    }
 }

Metrics/MetricExporterInterface.php

@@ -26,6 +26,4 @@ public function temporality(MetricMetadataInterface $metric);
     public function export(iterable $batch): bool;
 
     public function shutdown(): bool;
-
-    public function forceFlush(): bool;
 }

Metrics/MetricReader/ExportingReader.php

@@ -16,6 +16,7 @@
 use OpenTelemetry\SDK\Metrics\MetricSourceInterface;
 use OpenTelemetry\SDK\Metrics\MetricSourceProviderInterface;
 use OpenTelemetry\SDK\Metrics\MetricSourceRegistryInterface;
+use OpenTelemetry\SDK\Metrics\PushMetricExporterInterface;
 use OpenTelemetry\SDK\Metrics\StalenessHandlerInterface;
 use function spl_object_id;
 
@@ -139,10 +140,13 @@ public function forceFlush(): bool
         if ($this->closed) {
             return false;
         }
+        if ($this->exporter instanceof PushMetricExporterInterface) {
+            $collect = $this->doCollect();
+            $forceFlush = $this->exporter->forceFlush();
 
-        $collect = $this->doCollect();
-        $forceFlush = $this->exporter->forceFlush();
+            return $collect && $forceFlush;
+        }
 
-        return $collect && $forceFlush;
+        return true;
     }
 }

Metrics/PushMetricExporterInterface.php

@@ -0,0 +1,12 @@
+<?php
+
+declare(strict_types=1);
+
+namespace OpenTelemetry\SDK\Metrics;
+
+use OpenTelemetry\SDK\Metrics;
+
+interface PushMetricExporterInterface extends Metrics\MetricExporterInterface
+{
+    public function forceFlush(): bool;
+}