Revert "ProcessExit event handler improvements (#1332)" (#1410)

This reverts commit 0aaa30e.

src/Datadog.Trace/Tracer.cs

@@ -712,39 +712,7 @@ private void InitializeLibLogScopeEventSubscriber(IScopeManager scopeManager, st
 
         private void CurrentDomain_ProcessExit(object sender, EventArgs e)
         {
-            // This handles a graceful shutdown or a SIGTERM
-            // Multiple delegates can be registered to this event. (eg. IHostApplicationLifetime instances)
-            // So we must be sure we are the last handler of the event to ensure we are flushing all the
-            // possible traces we are generating.
-
-            // For this, we try to get the internal ProcessExit delegate from the event.
-            var processExitDelegate = DelegatesHelper.GetInternalProcessExitDelegate();
-            if (processExitDelegate != null)
-            {
-                // With the internal MulticastDelegate we first create the delegate instance
-                // we want to run at last of the event handler.
-
-                // Sets the final delegate to be executed by the ProcessExit event.
-                var lastDelegate = new EventHandler((s, earg) =>
-                {
-                    RunShutdownTasks();
-                });
-
-                // Try to modify the MulticastDelegate invocation list and set the last delegate.
-                if (!DelegatesHelper.TrySetLastDelegate(processExitDelegate, lastDelegate))
-                {
-                    // This means we are in the last delegate already
-                    // or we were unable to set the last delegate, in
-                    // any case we fallback by running the delegate now.
-                    RunShutdownTasks();
-                }
-            }
-            else
-            {
-                // If we were unable to extract the internal delegate of the event then
-                // we just fallback and run the code here.
-                RunShutdownTasks();
-            }
+            RunShutdownTasks();
         }
 
         private void CurrentDomain_UnhandledException(object sender, UnhandledExceptionEventArgs e)
@@ -755,69 +723,7 @@ private void CurrentDomain_UnhandledException(object sender, UnhandledExceptionE
 
         private void Console_CancelKeyPress(object sender, ConsoleCancelEventArgs e)
         {
-            // Console Cancel KeyPress is raised when CTRL+C or CTRL+BREAK are pressed in a console windows
-            // On Unix: is registered using SIGINT and SIGQUIT signals.
-            // On Windows: is registered with Kernel32.SetConsoleCtrlHandler.
-            // ...
-            // If ConsoleCancelEventArgs.Cancel is false then the Process will be exit without calling ProcessExit event. So we shuld flush and close.
-            // If ConsoleCancelEventArgs.Cancel is true the process will not exit so we will only flush.
-            // Because the Cancel property can be modified by the application handlers we should listen at the end of the queue.
-
-            // For this, we try to get the internal CancelKeyPress delegate from the event.
-            var cancelKeyPressDelegate = DelegatesHelper.GetInternalCancelKeyPressDelegate();
-            if (cancelKeyPressDelegate != null)
-            {
-                // With the internal MulticastDelegate we first create the delegate instance
-                // we want to run at last of the event handler.
-
-                // Sets the final delegate to be executed by the CancelKeyPress event.
-                var lastDelegate = new ConsoleCancelEventHandler(HandleCancelKeyPress);
-
-                // Try to modify the MulticastDelegate invocation list and set the last delegate.
-                if (!DelegatesHelper.TrySetLastDelegate(cancelKeyPressDelegate, lastDelegate))
-                {
-                    // This means we are in the last delegate already
-                    // or we were unable to set the last delegate, in
-                    // any case we fallback by running the delegate now.
-                    HandleCancelKeyPress(sender, e);
-                }
-            }
-            else
-            {
-                // If we were unable to extract the internal delegate of the event then
-                // we just fallback and run the code here.
-                HandleCancelKeyPress(sender, e);
-            }
-
-            void HandleCancelKeyPress(object s, ConsoleCancelEventArgs cEvtArgs)
-            {
-                if (cEvtArgs.Cancel)
-                {
-                    FlushTraces();
-                }
-                else
-                {
-                    RunShutdownTasks();
-                }
-            }
-
-            void FlushTraces()
-            {
-                SynchronizationContext context = SynchronizationContext.Current;
-                try
-                {
-                    SynchronizationContext.SetSynchronizationContext(null);
-                    _agentWriter.FlushTracesAsync().GetAwaiter().GetResult();
-                }
-                catch (Exception ex)
-                {
-                    Log.Error(ex, "Error flushing traces on shutdown.");
-                }
-                finally
-                {
-                    SynchronizationContext.SetSynchronizationContext(context);
-                }
-            }
+            RunShutdownTasks();
         }
 
         private void CurrentDomain_DomainUnload(object sender, EventArgs e)
@@ -827,20 +733,14 @@ private void CurrentDomain_DomainUnload(object sender, EventArgs e)
 
         private void RunShutdownTasks()
         {
-            SynchronizationContext context = SynchronizationContext.Current;
             try
             {
-                SynchronizationContext.SetSynchronizationContext(null);
-                _agentWriter.FlushAndCloseAsync().GetAwaiter().GetResult();
+                _agentWriter.FlushAndCloseAsync().Wait();
             }
             catch (Exception ex)
             {
                 Log.Error(ex, "Error flushing traces on shutdown.");
             }
-            finally
-            {
-                SynchronizationContext.SetSynchronizationContext(context);
-            }
         }
 
         private void HeartbeatCallback(object state)