Fix yet another deadlock in mocks (#946)

* Fix yet another deadlock in mocks

* tweak

Author: louis-z

NGitLab.Mock/Clients/ClientContext.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Diagnostics;
+using System.Runtime.CompilerServices;
 using System.Threading;
 
 namespace NGitLab.Mock.Clients;
@@ -14,10 +15,20 @@ internal sealed class ClientContext(GitLabServer server, User user)
 
     public bool IsAuthenticated => User != null;
 
-    public IDisposable BeginOperationScope()
+    public IDisposable BeginOperationScope(
+        [CallerMemberName] string callingMethod = null,
+        [CallerFilePath] string callingFilePath = null,
+        [CallerLineNumber] int callingLineNumber = -1)
     {
         Server.RaiseOnClientOperation();
-        return new Releaser(_operationLock);
+        var releaser = new Releaser(_operationLock);
+
+        // Store caller info for debugging purposes
+        Releaser.MethodWhereLockWasTaken = callingMethod;
+        Releaser.FilePathWhereLockWasTaken = callingFilePath;
+        Releaser.LineNumberWhereLockWasTaken = callingLineNumber;
+
+        return releaser;
     }
 
     private sealed class Releaser : IDisposable
@@ -27,11 +38,18 @@ private sealed class Releaser : IDisposable
         public Releaser(SemaphoreSlim operationLock)
         {
             _operationLock = operationLock;
-            if (Debugger.IsAttached && _operationLock.CurrentCount == 0)
+            if (_operationLock.CurrentCount == 0 && Debugger.IsAttached)
                 Debugger.Break();
             _operationLock.Wait();
         }
 
+        // The following is for debugging purposes only. It stores info about where the active lock was taken.
+        public static string MethodWhereLockWasTaken { get; set; }
+
+        public static string FilePathWhereLockWasTaken { get; set; }
+
+        public static int LineNumberWhereLockWasTaken { get; set; }
+
         public void Dispose()
         {
             _operationLock.Release();

NGitLab.Mock/Clients/RepositoryClient.cs

@@ -142,28 +142,33 @@ public CompareResults Compare(CompareQuery query)
     {
         using (Context.BeginOperationScope())
         {
-            var project = GetProject(_projectId, ProjectPermission.View);
-            var treeChanges = project.Repository.Compare(query.From, query.To);
-            return new CompareResults()
-            {
-                Diff = treeChanges.Select(change
-                    => new Diff()
-                    {
-                        NewPath = change.Path,
-                        OldPath = change.OldPath,
-                        IsNewFile = change.Status is ChangeKind.Added,
-                        IsDeletedFile = change.Status is ChangeKind.Deleted,
-                        IsRenamedFile = change.Status is ChangeKind.Renamed,
-                    }).ToArray(),
-            };
+            return CompareLockless(query);
         }
     }
 
+    private CompareResults CompareLockless(CompareQuery query)
+    {
+        var project = GetProject(_projectId, ProjectPermission.View);
+        var treeChanges = project.Repository.Compare(query.From, query.To);
+        return new CompareResults()
+        {
+            Diff = treeChanges.Select(change
+                => new Diff()
+                {
+                    NewPath = change.Path,
+                    OldPath = change.OldPath,
+                    IsNewFile = change.Status is ChangeKind.Added,
+                    IsDeletedFile = change.Status is ChangeKind.Deleted,
+                    IsRenamedFile = change.Status is ChangeKind.Renamed,
+                }).ToArray(),
+        };
+    }
+
     public Task<CompareResults> CompareAsync(CompareQuery query, CancellationToken cancellationToken = default)
     {
         using (Context.BeginOperationScope())
         {
-            return Task.FromResult(Compare(query));
+            return Task.FromResult(CompareLockless(query));
         }
     }
 }