chore: Use Task.WhenAny's output to avoid a double await

Also enable tests for PeriodicExportingMetricReaderTaskWorker to improve coverage

Author: jeromelaban

src/OpenTelemetry/Internal/PeriodicExportingMetricReaderTaskWorker.cs

@@ -127,10 +127,13 @@ private async Task ExporterProcAsync()
             {
                 var timeout = (int)(this.exportIntervalMilliseconds - (sw.ElapsedMilliseconds % this.exportIntervalMilliseconds));
 
+                var exportTriggerTask = this.exportTrigger.WaitAsync(cancellationToken);
+                Task? triggeredTask = null;
+
                 try
                 {
-                    await Task.WhenAny(
-                        this.exportTrigger.WaitAsync(cancellationToken),
+                    triggeredTask = await Task.WhenAny(
+                        exportTriggerTask,
                         Task.Delay(timeout, cancellationToken)).ConfigureAwait(false);
                 }
                 catch (OperationCanceledException)
@@ -151,9 +154,9 @@ await Task.WhenAny(
                 }
 
                 // Check if the trigger was signaled by trying to acquire it with a timeout of 0
-                var wasTriggered = await this.exportTrigger.WaitAsync(0, cancellationToken).ConfigureAwait(false);
+                var exportWasTriggered = triggeredTask == exportTriggerTask;
 
-                if (wasTriggered)
+                if (exportWasTriggered)
                 {
                     OpenTelemetrySdkEventSource.Log.MetricReaderEvent("PeriodicExportingMetricReader calling MetricReader.Collect because Export was triggered.");
                 }

test/OpenTelemetry.Tests/Internal/PeriodicExportingMetricReaderHelperTests.cs

@@ -149,6 +149,6 @@ private static PeriodicExportingMetricReader CreatePeriodicExportingMetricReader
 #pragma warning disable CA2000 // Dispose objects before losing scope
         var dummyMetricExporter = new InMemoryExporter<Metric>(Array.Empty<Metric>());
 #pragma warning restore CA2000 // Dispose objects before losing scope
-        return PeriodicExportingMetricReaderHelper.CreatePeriodicExportingMetricReader(dummyMetricExporter, options, useThreads: true);
+        return PeriodicExportingMetricReaderHelper.CreatePeriodicExportingMetricReader(dummyMetricExporter, options, useThreads: useThreads);
     }
 }

test/OpenTelemetry.Tests/Metrics/MetricPointReclaimTests.cs

@@ -2,6 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0
 
 using System.Diagnostics.Metrics;
+using Microsoft.ApplicationInsights.Extensibility.Implementation;
 using OpenTelemetry.Tests;
 using Xunit;
 
@@ -10,9 +11,11 @@ namespace OpenTelemetry.Metrics.Tests;
 public class MetricPointReclaimTests
 {
     [Theory]
-    [InlineData(false)]
-    [InlineData(true)]
-    public void MeasurementsAreNotDropped(bool emitMetricWithNoDimensions)
+    [InlineData(false, false)]
+    [InlineData(true, false)]
+    [InlineData(false, true)]
+    [InlineData(true, true)]
+    public void MeasurementsAreNotDropped(bool emitMetricWithNoDimensions, bool useThreads)
     {
         using var meter = new Meter(Utils.GetCurrentMethodName());
         var counter = meter.CreateCounter<long>("MyFruitCounter");
@@ -21,7 +24,7 @@ public void MeasurementsAreNotDropped(bool emitMetricWithNoDimensions)
         int maxNumberofDistinctMetricPoints = 4000; // Default max MetricPoints * 2
 
         using var exporter = new CustomExporter(assertNoDroppedMeasurements: true);
-        using var metricReader = new PeriodicExportingMetricReader(exporter, exportIntervalMilliseconds: 10)
+        using var metricReader = new PeriodicExportingMetricReader(exporter, exportIntervalMilliseconds: 10, useThreads: useThreads)
         {
             TemporalityPreference = MetricReaderTemporalityPreference.Delta,
         };