Lingering File Handles (#71)

Fixing a bug where in various situations, the files used for temporary storage of query results would be leftover. In particular, the following changes were made:
* When the dispose query request is submitted, the corresponding query is now disposed in addition from being removed from the list of active queries
* When a query is cancelled, it is disposed after it is cancelled
* If a query already exists for a given ownerURI, the existing query is disposed before creating a new query
* All queries are disposed when the query execution service is disposed (ie, at shutdown of the service)

A unit test to verify the action of the dispose method for a ResultSet was added.

* Ensuring queries are disposed

Adding logic to dispose any queries when:
* URI that already has a query executes another query
* A request to dispose a query is submitted
* A request to cancel a query is submitted

* Small tweaks for cleanup of query execution service

src/Microsoft.SqlTools.ServiceLayer/QueryExecution/QueryExecutionService.cs

@@ -13,6 +13,7 @@ using Microsoft.SqlTools.ServiceLayer.Hosting.Protocol;
 using Microsoft.SqlTools.ServiceLayer.QueryExecution.Contracts;
 using Microsoft.SqlTools.ServiceLayer.QueryExecution.DataStorage;
 using Microsoft.SqlTools.ServiceLayer.SqlContext;
+using Microsoft.SqlTools.ServiceLayer.Utility;
 using Microsoft.SqlTools.ServiceLayer.Workspace;
 using Microsoft.SqlTools.ServiceLayer.Workspace.Contracts;
 using Newtonsoft.Json;
@@ -207,6 +208,9 @@ namespace Microsoft.SqlTools.ServiceLayer.QueryExecution
                     return;
                 }
 
+                // Cleanup the query
+                result.Dispose();
+
                 // Success
                 await requestContext.SendResult(new QueryDisposeResult
                 {
@@ -237,6 +241,7 @@ namespace Microsoft.SqlTools.ServiceLayer.QueryExecution
 
                 // Cancel the query
                 result.Cancel();
+                result.Dispose();
 
                 // Attempt to dispose the query
                 if (!ActiveQueries.TryRemove(cancelParams.OwnerUri, out result))
@@ -268,7 +273,7 @@ namespace Microsoft.SqlTools.ServiceLayer.QueryExecution
         /// <summary>
         /// Process request to save a resultSet to a file in CSV format
         /// </summary>
-        public async Task HandleSaveResultsAsCsvRequest( SaveResultsAsCsvRequestParams saveParams,
+        public async Task HandleSaveResultsAsCsvRequest(SaveResultsAsCsvRequestParams saveParams,
             RequestContext<SaveResultRequestResult> requestContext)
         {
             // retrieve query for OwnerUri
@@ -341,7 +346,7 @@ namespace Microsoft.SqlTools.ServiceLayer.QueryExecution
         /// <summary>
         /// Process request to save a resultSet to a file in JSON format
         /// </summary>
-        public async Task HandleSaveResultsAsJsonRequest( SaveResultsAsJsonRequestParams saveParams,
+        public async Task HandleSaveResultsAsJsonRequest(SaveResultsAsJsonRequestParams saveParams,
             RequestContext<SaveResultRequestResult> requestContext)
         {
             // retrieve query for OwnerUri
@@ -422,6 +427,7 @@ namespace Microsoft.SqlTools.ServiceLayer.QueryExecution
                 await requestContext.SendError(ex.Message);
             }
         }
+
         #endregion
 
         #region Private Helpers
@@ -445,6 +451,7 @@ namespace Microsoft.SqlTools.ServiceLayer.QueryExecution
                 Query oldQuery;
                 if (ActiveQueries.TryGetValue(executeParams.OwnerUri, out oldQuery) && oldQuery.HasExecuted)
                 {
+                    oldQuery.Dispose();
                     ActiveQueries.TryRemove(executeParams.OwnerUri, out oldQuery);
                 }
 
@@ -546,8 +553,22 @@ namespace Microsoft.SqlTools.ServiceLayer.QueryExecution
             {
                 foreach (var query in ActiveQueries)
                 {
+                    if (!query.Value.HasExecuted)
+                    {
+                        try
+                        {
+                            query.Value.Cancel();
+                        }
+                        catch (Exception e)
+                        {
+                            // We don't particularly care if we fail to cancel during shutdown
+                            string message = string.Format("Failed to cancel query {0} during query service disposal: {1}", query.Key, e);
+                            Logger.Write(LogLevel.Warning, message);
+                        }
+                    }
                     query.Value.Dispose();
                 }
+                ActiveQueries.Clear();
             }
 
             disposed = true;