Simplify and fix the detection of XEL fields / actions (#117)

* Fixes a exception being raised when extracting fields / actions from
  multiple XEL files, and if the earlier file had reached sampling
  limit.

* Removes cancellation support for this XEL fields / action detection
  method, thereby simplifying the implementation. As this method is
  typically very quick (as it is sampled) the lack of cancellation is
  acceptable.

Author: arvindsh

Engine/StackResolver.cs

@@ -29,8 +29,8 @@ public class StackResolver : IDisposable {
         private static readonly Regex rgxAlreadySymbolizedFrame = new (@"((?<framenum>\d+)\s+)*(?<module>\w+)(\.(dll|exe))*!(?<symbolizedfunc>.+?)\s*\+\s*(0[xX])*(?<offset>[0-9a-fA-F]+)\s*", rgxOptions);
         private static readonly Regex rgxmoduleaddress = new (@"^\s*(?<filepath>.+)(\t+| +)(?<baseaddress>(0x)?[0-9a-fA-F`]+)\s*$", RegexOptions.Multiline);
 
-        public Task<Tuple<List<string>, List<string>>> GetDistinctXELFieldsAsync(string[] xelFiles, int eventsToSample, CancellationTokenSource cts) {
-            return XELHelper.GetDistinctXELActionsFieldsAsync(xelFiles, eventsToSample, cts);
+        public Task<Tuple<List<string>, List<string>>> GetDistinctXELFieldsAsync(string[] xelFiles, int eventsToSample) {
+            return XELHelper.GetDistinctXELActionsFieldsAsync(xelFiles, eventsToSample);
         }
 
         /// Public method which to help import XEL files

Engine/XELHelper.cs

@@ -78,29 +78,27 @@ await xeStream.ReadEventStream(evt => {
             });
         }
 
-        internal async static Task<Tuple<List<string>, List<string>>> GetDistinctXELActionsFieldsAsync(string[] xelFiles, int eventsToSampleFromEachFile, CancellationTokenSource cts) {
+        internal async static Task<Tuple<List<string>, List<string>>> GetDistinctXELActionsFieldsAsync(string[] xelFiles, int eventsToSampleFromEachFile) {
             return await Task.Run(async () => {
                 Contract.Requires(xelFiles != null && eventsToSampleFromEachFile > 0);
                 var allActions = new HashSet<string>();
                 var allFields = new HashSet<string>();
-                bool internalCancel = false;
                 foreach (var file in xelFiles) {
                     var numEvents = 0;
                     var xeStream = new XEFileEventStreamer(file);
                     try {
+                        // If preceeding file had issued an "internal cancel" (due to number of sampled events reached)
+                        // then create a new CTS to ensure subsequent files (if any) are also sampled correctly.
+                        using var cts = new CancellationTokenSource();
                         await xeStream.ReadEventStream(evt => {
-                                if (Interlocked.Increment(ref numEvents) > eventsToSampleFromEachFile) {
-                                    internalCancel = true;
-                                    cts.Cancel();
-                                }
+                                if (Interlocked.Increment(ref numEvents) > eventsToSampleFromEachFile) cts.Cancel();
                                 lock (allActions) evt.Actions.Select(action => allActions.Add(action.Key)).Count();
                                 lock (allFields) evt.Fields.Select(field => allFields.Add(field.Key)).Count();
                                 return Task.CompletedTask;
                             }, cts.Token);
                     } catch (AggregateException e) {
-                        if (e.InnerException is OperationCanceledException) if (!internalCancel) return new Tuple<List<string>, List<string>>(new List<string>(), new List<string>());
-                            else throw;
-                    } catch (OperationCanceledException) { if (!internalCancel) return new Tuple<List<string>, List<string>>(new List<string>(), new List<string>()); }
+                        if (e.InnerException is not OperationCanceledException) throw;
+                    } catch (OperationCanceledException) { /* nothing to do, as cancel the operation at the end of sampling */ }
                 }
 
                 return new Tuple<List<string>, List<string>>(allActions.OrderBy(k => k).ToList(), allFields.OrderBy(k => k).ToList());

GUI/MainForm.cs

@@ -223,9 +223,8 @@ private async void CallStackInput_DragDrop(object sender, DragEventArgs e) {
 
         private async Task<List<string>> GetUserSelectedXEFieldsAsync(string[] fileNames) {
             using var fieldsListDialog = new FieldSelection();
-            using var cts = new CancellationTokenSource();
             fieldsListDialog.Text = "Select relevant XEvent fields";
-            var xeEventItems = await this._resolver.GetDistinctXELFieldsAsync(fileNames, 1000, cts);
+            var xeEventItems = await this._resolver.GetDistinctXELFieldsAsync(fileNames, 1000);
             if (xeEventItems.Item1.Count + xeEventItems.Item2.Count == 0) return new List<string>();
             fieldsListDialog.AllActions = xeEventItems.Item1;
             fieldsListDialog.AllFields = xeEventItems.Item2;

Tests/Tests.cs

@@ -305,8 +305,7 @@ private string PrepareLargeXEventInput() {
 
         [TestMethod][TestCategory("Unit")] public async Task XELActionsAndFieldsAsync() {
             using var csr = new StackResolver();
-            using var cts = new CancellationTokenSource();
-            var ret = await csr.GetDistinctXELFieldsAsync(new[] { @"..\..\..\Tests\TestCases\ImportXEL\xe_wait_completed_0_132353446563350000.xel" }, 1000, cts);
+            var ret = await csr.GetDistinctXELFieldsAsync(new[] { @"..\..\..\Tests\TestCases\ImportXEL\xe_wait_completed_0_132353446563350000.xel" }, 5);
             Assert.AreEqual(1, ret.Item1.Count);   // just the callstack action
             Assert.AreEqual("callstack", ret.Item1.First());    // verify the name
             Assert.AreEqual(5, ret.Item2.Count);   // 5 fields
@@ -316,8 +315,7 @@ private string PrepareLargeXEventInput() {
 
         [TestMethod][TestCategory("Unit")] public async Task XELActionsAndFieldsAsyncMultipleFiles() {
             using var csr = new StackResolver();
-            using var cts = new CancellationTokenSource();
-            var ret = await csr.GetDistinctXELFieldsAsync(new[] { @"..\..\..\Tests\TestCases\ImportXEL\xe_wait_completed_0_132353446563350000.xel", @"..\..\..\Tests\TestCases\ImportXEL\XESpins_0_131627061603030000.xel" }, 1000, cts);
+            var ret = await csr.GetDistinctXELFieldsAsync(new[] { @"..\..\..\Tests\TestCases\ImportXEL\xe_wait_completed_0_132353446563350000.xel", @"..\..\..\Tests\TestCases\ImportXEL\XESpins_0_131627061603030000.xel" }, 5);
             Assert.AreEqual(1, ret.Item1.Count);   // just the callstack action
             Assert.AreEqual("callstack", ret.Item1.First());    // verify the name
             Assert.AreEqual(9, ret.Item2.Count);   // 9 fields in total across the 2 XEL files
@@ -776,15 +774,6 @@ private string PrepareLargeXEventInput() {
             Assert.AreEqual(0, xelTask.Result.Item1);
             Assert.AreEqual(StackResolver.OperationCanceled, xelTask.Result.Item2);
 
-            using var cts2 = new CancellationTokenSource();
-            var xelFieldsTask = csr.GetDistinctXELFieldsAsync(new[] { @"..\..\..\Tests\TestCases\ImportXEL\XESpins_0_131627061603030000.xel" }, int.MaxValue, cts2);
-            while (true) {
-                if (xelFieldsTask.Wait(StackResolver.OperationWaitIntervalMilliseconds)) break;
-                cts2.Cancel();
-            }
-            Assert.AreEqual(0, xelFieldsTask.Result.Item1.Count);
-            Assert.AreEqual(0, xelFieldsTask.Result.Item2.Count);
-
             Assert.IsTrue(csr.ProcessBaseAddresses(@"c:\mssql\binn\sqldk.dll 00000001`00400000"));
             var xeventInput = PrepareLargeXEventInput().ToString();
             using var cts3 = new CancellationTokenSource();