perf: stop the previous preview before matching the new path

QuickLook/Helpers/KeyboardLog.cs

@@ -0,0 +1,102 @@
+// Copyright © 2017-2026 QL-Win Contributors
+//
+// This file is part of QuickLook program.
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+using QuickLook.Common.Helpers;
+using System;
+using System.Collections.Concurrent;
+using System.IO;
+using System.Text;
+using System.Threading;
+
+namespace QuickLook.Helpers;
+
+/// <summary>
+/// Diagnostic log for the keyboard pipeline, written to QuickLook.Keyboard.log in the data folder.
+/// Only QuickLook's own keys and anomalies are logged, never other keystrokes.
+/// </summary>
+internal static class KeyboardLog
+{
+    private const long MAX_SIZE = 512 * 1024;
+
+    /// <summary>Preview phases slower than this block switching to the next file and get logged.</summary>
+    private const long SLOW_PREVIEW_PHASE_MS = 100;
+
+    private static readonly string LogPath = Path.Combine(SettingHelper.LocalDataPath, "QuickLook.Keyboard.log");
+
+    // Bounded so that a stuck disk can never make the keyboard hook wait or grow memory.
+    private static readonly BlockingCollection<string> Queue = new(new ConcurrentQueue<string>(), 1000);
+
+    static KeyboardLog()
+    {
+        new Thread(WriteLoop)
+        {
+            IsBackground = true,
+            Name = "QuickLook.KeyboardLog",
+            Priority = ThreadPriority.BelowNormal,
+        }.Start();
+    }
+
+    /// <summary>
+    /// Never blocks; safe to call from inside the low-level keyboard hook.
+    /// </summary>
+    public static void Write(string message)
+    {
+        Queue.TryAdd($"{DateTime.Now:yyyy-MM-dd HH:mm:ss.fff} [T{Thread.CurrentThread.ManagedThreadId}] {message}");
+    }
+
+    /// <summary>
+    /// Logs a preview phase that ran on the UI thread only when it was slow enough to delay
+    /// the next selection change, naming the plugin and file type, never the file name.
+    /// </summary>
+    public static void WriteIfSlow(string phase, long elapsedMs)
+    {
+        if (elapsedMs >= SLOW_PREVIEW_PHASE_MS)
+            Write($"Slow preview {phase}: {elapsedMs} ms");
+    }
+
+    private static void WriteLoop()
+    {
+        var batch = new StringBuilder();
+
+        foreach (var line in Queue.GetConsumingEnumerable())
+        {
+            batch.AppendLine(line);
+            while (Queue.TryTake(out var more))
+                batch.AppendLine(more);
+
+            try
+            {
+                Directory.CreateDirectory(Path.GetDirectoryName(LogPath)!);
+
+                var file = new FileInfo(LogPath);
+                if (file.Exists && file.Length > MAX_SIZE)
+                {
+                    File.Delete(LogPath + ".old");
+                    File.Move(LogPath, LogPath + ".old");
+                }
+
+                File.AppendAllText(LogPath, batch.ToString());
+            }
+            catch
+            {
+                // logging must never take QuickLook down
+            }
+
+            batch.Clear();
+        }
+    }
+}

QuickLook/ViewWindowManager.cs

@@ -164,8 +164,19 @@ public void InvokePreview(string path = null)
 
         RunFocusMonitor();
 
+        // Stop the previous preview's background work (file reads, folder counting...) before
+        // matching the new path, so it doesn't keep competing for the disk while plugins probe it.
+        var sw = Stopwatch.StartNew();
+        _viewerWindow.UnloadPlugin();
+        var unloadMs = sw.ElapsedMilliseconds;
+
+        sw.Restart();
         var matchedPlugin = PluginManager.GetInstance().FindMatch(path);
 
+        var fileType = isDirectory ? "<dir>" : Path.GetExtension(path);
+        KeyboardLog.WriteIfSlow("unload", unloadMs);
+        KeyboardLog.WriteIfSlow($"match ({fileType} -> {matchedPlugin.GetType().Namespace})", sw.ElapsedMilliseconds);
+
         BeginShowNewWindow(path, matchedPlugin);
     }
 

QuickLook/ViewerWindow.Actions.cs

@@ -253,7 +253,10 @@ internal void UnloadPlugin()
 
         try
         {
+            var cleanupWatch = Stopwatch.StartNew();
             Plugin?.Cleanup();
+            if (Plugin != null)
+                KeyboardLog.WriteIfSlow($"cleanup ({Plugin.GetType().Namespace})", cleanupWatch.ElapsedMilliseconds);
         }
         catch (Exception e)
         {
@@ -284,9 +287,11 @@ internal void BeginShow(IViewer matchedPlugin, string path,
         ContextObject.ColorProfileName = DisplayDeviceHelper.GetMonitorColorProfileFromWindow(this);
 
         // Get window size before showing it
+        var prepareWatch = Stopwatch.StartNew();
         try
         {
             Plugin.Prepare(path, ContextObject);
+            KeyboardLog.WriteIfSlow($"prepare ({Plugin.GetType().Namespace})", prepareWatch.ElapsedMilliseconds);
         }
         catch (Exception e)
         {
@@ -360,7 +365,9 @@ internal void BeginShow(IViewer matchedPlugin, string path,
                 // Avoid main thread scheduling lag
                 if (Plugin is null) return;
 
+                var viewWatch = Stopwatch.StartNew();
                 Plugin.View(path, ContextObject);
+                KeyboardLog.WriteIfSlow($"view ({Plugin.GetType().Namespace})", viewWatch.ElapsedMilliseconds);
 
                 // Initial the more menu
                 ClearMoreMenuUnpin();