Add ForceFlush to TracerProvider (#1837)

* Add ForceFlush to TracerProvider

* Fixed inlinedoc

* Change the wording

* Remove creating activity

* Update src/OpenTelemetry/CHANGELOG.md

Co-authored-by: Cijo Thomas <cithomas@microsoft.com>

Co-authored-by: Cijo Thomas <cithomas@microsoft.com>

src/OpenTelemetry/.publicApi/net452/PublicAPI.Unshipped.txt

@@ -0,0 +1 @@
+static OpenTelemetry.Trace.TracerProviderExtensions.ForceFlush(this OpenTelemetry.Trace.TracerProvider provider, int timeoutMilliseconds = -1) -> bool

src/OpenTelemetry/.publicApi/net46/PublicAPI.Unshipped.txt

@@ -0,0 +1 @@
+static OpenTelemetry.Trace.TracerProviderExtensions.ForceFlush(this OpenTelemetry.Trace.TracerProvider provider, int timeoutMilliseconds = -1) -> bool

src/OpenTelemetry/.publicApi/net461/PublicAPI.Unshipped.txt

@@ -0,0 +1 @@
+static OpenTelemetry.Trace.TracerProviderExtensions.ForceFlush(this OpenTelemetry.Trace.TracerProvider provider, int timeoutMilliseconds = -1) -> bool

src/OpenTelemetry/.publicApi/netstandard2.0/PublicAPI.Unshipped.txt

@@ -0,0 +1 @@
+static OpenTelemetry.Trace.TracerProviderExtensions.ForceFlush(this OpenTelemetry.Trace.TracerProvider provider, int timeoutMilliseconds = -1) -> bool

src/OpenTelemetry/CHANGELOG.md

@@ -9,6 +9,8 @@ please check the latest changes
 
 ## Unreleased
 
+* Added `ForceFlush` to `TracerProvider`. ([#1837](https://github.com/open-telemetry/opentelemetry-dotnet/pull/1837))
+
 ## 1.0.1
 
 Released 2021-Feb-10

src/OpenTelemetry/Trace/TracerProviderExtensions.cs

@@ -43,6 +43,52 @@ public static TracerProvider AddProcessor(this TracerProvider provider, BaseProc
             return provider;
         }
 
+        /// <summary>
+        /// Flushes the all the processors at TracerProviderSdk, blocks the current thread until flush
+        /// completed, shutdown signaled or timed out.
+        /// </summary>
+        /// <param name="provider">TracerProviderSdk instance on which ForceFlush will be called.</param>
+        /// <param name="timeoutMilliseconds">
+        /// The number of milliseconds to wait, or <c>Timeout.Infinite</c> to
+        /// wait indefinitely.
+        /// </param>
+        /// <returns>
+        /// Returns <c>true</c> when force flush succeeded; otherwise, <c>false</c>.
+        /// </returns>
+        /// <exception cref="System.ArgumentOutOfRangeException">
+        /// Thrown when the <c>timeoutMilliseconds</c> is smaller than -1.
+        /// </exception>
+        /// <remarks>
+        /// This function guarantees thread-safety.
+        /// </remarks>
+        public static bool ForceFlush(this TracerProvider provider, int timeoutMilliseconds = Timeout.Infinite)
+        {
+            if (provider == null)
+            {
+                throw new ArgumentNullException(nameof(provider));
+            }
+
+            if (provider is TracerProviderSdk tracerProviderSdk)
+            {
+                if (timeoutMilliseconds < 0 && timeoutMilliseconds != Timeout.Infinite)
+                {
+                    throw new ArgumentOutOfRangeException(nameof(timeoutMilliseconds), timeoutMilliseconds, "timeoutMilliseconds should be non-negative.");
+                }
+
+                try
+                {
+                    return tracerProviderSdk.OnForceFlush(timeoutMilliseconds);
+                }
+                catch (Exception ex)
+                {
+                    OpenTelemetrySdkEventSource.Log.TracerProviderException(nameof(tracerProviderSdk.OnForceFlush), ex);
+                    return false;
+                }
+            }
+
+            return true;
+        }
+
         /// <summary>
         /// Attempts to shutdown the TracerProviderSdk, blocks the current thread until
         /// shutdown completed or timed out.

src/OpenTelemetry/Trace/TracerProviderSdk.cs

@@ -207,6 +207,11 @@ internal TracerProviderSdk AddProcessor(BaseProcessor<Activity> processor)
             return this;
         }
 
+        internal bool OnForceFlush(int timeoutMilliseconds)
+        {
+            return this.processor?.ForceFlush(timeoutMilliseconds) ?? true;
+        }
+
         /// <summary>
         /// Called by <c>Shutdown</c>. This function should block the current
         /// thread until shutdown completed or timed out.

test/OpenTelemetry.Tests/Trace/TracerProviderSdkTest.cs

@@ -398,6 +398,21 @@ public void TracerProviderSdkBuildsWithSDKResource()
             Assert.Single(versionAttribute);
         }
 
+        [Fact]
+        public void TracerProviderSdkFlushesProcessorForcibly()
+        {
+            using TestActivityProcessor testActivityProcessor = new TestActivityProcessor();
+
+            using var tracerProvider = Sdk.CreateTracerProviderBuilder()
+                        .AddProcessor(testActivityProcessor)
+                        .Build();
+
+            var isFlushed = tracerProvider.ForceFlush();
+
+            Assert.True(isFlushed);
+            Assert.True(testActivityProcessor.ForceFlushCalled);
+        }
+
         public void Dispose()
         {
             GC.SuppressFinalize(this);