Improve RevisionDataGridView responsiveness

(cherry picked from commit 4bbe805)

GitUI/UserControls/RevisionGrid/RevisionDataGridView.BackgroundUpdater.cs

@@ -0,0 +1,68 @@
+using System;
+using System.Threading.Tasks;
+
+namespace GitUI.UserControls.RevisionGrid
+{
+    public sealed partial class RevisionDataGridView
+    {
+        /// <summary>
+        /// Coordinates background update executions. Requested reruns only "queue up" upto one.
+        /// </summary>
+        private class BackgroundUpdater
+        {
+            private readonly Func<Task> _operation;
+            private readonly int _cooldownMilliseconds;
+            private readonly object _sync = new();
+
+            private volatile bool _executing;
+            private volatile bool _rerunRequested;
+
+            public BackgroundUpdater(Func<Task> operation, int cooldownMilliseconds)
+            {
+                _operation = operation ?? throw new ArgumentNullException(nameof(operation));
+                _cooldownMilliseconds = cooldownMilliseconds;
+            }
+
+            public void ScheduleExcecution()
+            {
+                lock (_sync)
+                {
+                    if (!_executing)
+                    {
+                        // if not running, start it
+                        _executing = true;
+                        Task.Run(WrappedOperationAsync);
+                    }
+                    else
+                    {
+                        // if currently running make sure it runs again
+                        _rerunRequested = true;
+                    }
+                }
+            }
+
+            private async Task WrappedOperationAsync()
+            {
+                await _operation();
+
+                if (_rerunRequested)
+                {
+                    await Task.Delay(_cooldownMilliseconds);
+                }
+
+                lock (_sync)
+                {
+                    if (_rerunRequested)
+                    {
+                        Task.Run(WrappedOperationAsync);
+                        _rerunRequested = false;
+                    }
+                    else
+                    {
+                        _executing = false;
+                    }
+                }
+            }
+        }
+    }
+}