SEBWIN-361: Fixed concurrency issue when terminating external applications and ensured termination operation continues even with failure.

SafeExamBrowser.Applications/ExternalApplication.cs

@@ -81,6 +81,7 @@ namespace SafeExamBrowser.Applications
 			{
 				logger.Info("Starting application...");
 				InitializeInstance(processFactory.StartNew(executablePath));
+				logger.Info("Successfully started application.");
 			}
 			catch (Exception e)
 			{
@@ -92,19 +93,29 @@ namespace SafeExamBrowser.Applications
 		{
 			applicationMonitor.InstanceStarted -= ApplicationMonitor_InstanceStarted;
 
+			try
+			{
 				lock (@lock)
 				{
 					if (instances.Any() && !settings.AllowRunning)
 					{
-					logger.Info("Terminating application...");
+						logger.Info($"Terminating application with {instances.Count} instance(s)...");
 
 						foreach (var instance in instances)
 						{
+							instance.Terminated -= Instance_Terminated;
 							instance.Terminate();
 						}
+
+						logger.Info("Successfully terminated application.");
 					}
 				}
 			}
+			catch (Exception e)
+			{
+				logger.Error($"Failed to terminate application!", e);
+			}
+		}
 
 		private void ApplicationMonitor_InstanceStarted(Guid applicationId, IProcess process)
 		{

SafeExamBrowser.Applications/ExternalApplicationInstance.cs

@@ -66,7 +66,11 @@ namespace SafeExamBrowser.Applications
 
 			var terminated = process.HasTerminated;
 
-			if (!terminated)
+			if (terminated)
+			{
+				logger.Info("Application instance is already terminated.");
+			}
+			else
 			{
 				FinalizeEvents();