Initial commit: FluidExplorer：从零实现的 WinUI 3 文件资源管理器替代品（Mica、命令栏、面包屑）
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WpyQwq
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using System.Buffers.Binary;
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using System.Collections.Concurrent;
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using System.Runtime.InteropServices;
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using System.Threading;
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using Microsoft.Win32.SafeHandles;
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namespace FluidExplorer.Services.Search.Usn;
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/// <summary>
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/// 增量监听的<b>回退通道</b>：ReadDirectoryChangesW。
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///
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/// 什么情况下用：USN 变更日志不可用（卷上没日志且没权限创建、被策略禁用、日志刚被删除等）。
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/// 这条路径不需要任何特殊权限，普通用户也能跑，从而保证「索引实时」这个卖点不落空。
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///
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/// 与 USN 的差别与应对：
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/// * RDCW 只给相对<b>路径</b>，不给 FRN。这里用 CreateFileW(FILE_READ_ATTRIBUTES) +
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/// GetFileInformationByHandle 取句柄上的 FileIndex —— 它与 USN 的 FRN 完全同口径
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/// （低 48 位记录号 + 高 16 位序列号），因此能直接命中同一个索引条目。
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/// * 新增/改名/内容变化都伴随着文件仍然存在，可以 stat 出来 → 直接 upsert。
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/// * 删除只剩一个路径（stat 必然失败），无法反查 FRN。应对：把受影响的<b>目录</b>记下来，
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/// 批处理结束后对该目录做一次「磁盘现状 vs 索引」的对账（<see cref="UsnVolumeIndex.ResyncDirectoryFromDisk"/>），
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/// 只把索引里存在、磁盘上已消失的孩子打墓碑。对账按目录去重、每轮有上限，代价可控。
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/// </summary>
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internal sealed class DirectoryChangeWatcher
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{
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private const int ReadBufferSize = 64 * 1024;
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/// <summary>每轮最多对账多少个目录，防止一次批量删除把 CPU 打满。</summary>
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private const int MaxResyncDirectoriesPerPass = 256;
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private static readonly uint NotifyFilter =
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UsnNative.FILE_NOTIFY_CHANGE_FILE_NAME |
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UsnNative.FILE_NOTIFY_CHANGE_DIR_NAME |
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UsnNative.FILE_NOTIFY_CHANGE_SIZE |
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UsnNative.FILE_NOTIFY_CHANGE_LAST_WRITE |
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UsnNative.FILE_NOTIFY_CHANGE_ATTRIBUTES;
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private readonly UsnVolumeIndex _index;
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private readonly string _root;
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private readonly ConcurrentDictionary<string, ulong> _directoryFrnCache = new(StringComparer.OrdinalIgnoreCase);
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private readonly HashSet<string> _pendingResync = new(StringComparer.OrdinalIgnoreCase);
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private readonly List<string> _resyncScratch = [];
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private SafeFileHandle? _handle;
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private volatile bool _stopRequested;
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internal DirectoryChangeWatcher(UsnVolumeIndex index)
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{
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_index = index;
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_root = index.VolumeRoot;
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}
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/// <summary>打断阻塞中的 ReadDirectoryChangesW：置停止标志 + 关目录句柄（双保险）。</summary>
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internal void RequestStop()
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{
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_stopRequested = true;
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Interlocked.Exchange(ref _handle, null)?.Dispose();
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}
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/// <summary>打开卷根目录句柄。返回 false 时 <paramref name="error"/> 给出中文原因。</summary>
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internal bool TryOpen(out string? error)
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{
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error = null;
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var handle = UsnNative.CreateFileW(
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_root,
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UsnNative.FILE_LIST_DIRECTORY,
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UsnNative.FILE_SHARE_READ | UsnNative.FILE_SHARE_WRITE | UsnNative.FILE_SHARE_DELETE,
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IntPtr.Zero,
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UsnNative.OPEN_EXISTING,
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UsnNative.FILE_FLAG_BACKUP_SEMANTICS, // 打开目录必须带这个
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IntPtr.Zero);
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if (handle.IsInvalid)
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{
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int openError = Marshal.GetLastWin32Error();
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handle.Dispose();
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error = UsnNative.DescribeError(openError, $"无法以 FILE_LIST_DIRECTORY 打开 {_root}");
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return false;
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}
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Volatile.Write(ref _handle, handle);
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return true;
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}
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/// <summary>阻塞式监听循环，直到 <see cref="RequestStop"/> 或句柄被关闭。</summary>
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internal void Run()
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{
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var handle = Volatile.Read(ref _handle);
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if (handle is null) return;
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var buffer = new byte[ReadBufferSize];
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try
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{
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while (!_stopRequested)
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{
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uint returned;
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bool ok;
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unsafe
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{
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fixed (byte* p = buffer)
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{
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ok = UsnNative.ReadDirectoryChangesW(
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handle, p, (uint)buffer.Length, true, NotifyFilter, out returned, IntPtr.Zero, IntPtr.Zero);
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}
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}
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if (!ok)
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{
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int readError = Marshal.GetLastWin32Error();
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if (_stopRequested
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|| readError is UsnNative.ERROR_OPERATION_ABORTED or UsnNative.ERROR_CANCELLED or UsnNative.ERROR_INVALID_HANDLE)
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{
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break;
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}
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// 单次失败不放弃：报给 UI 后继续（例如枚举期间目录被临时独占）
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_index.ReportWatchIssue($"ReadDirectoryChangesW 出错：{UsnNative.DescribeError(readError)}");
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continue;
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}
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if (returned == 0)
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{
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// 变更缓冲区溢出：期间的事件已经丢了，只能提示 UI 做一次重建
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_index.ReportWatchIssue("变更缓冲区溢出，部分变更已丢失，建议重建索引以保持一致。");
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continue;
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}
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ProcessEvents(buffer.AsSpan(0, (int)returned));
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FlushPendingResync();
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}
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}
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finally
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{
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Interlocked.Exchange(ref _handle, null)?.Dispose();
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}
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}
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private void ProcessEvents(ReadOnlySpan<byte> buffer)
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{
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int offset = 0;
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while (true)
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{
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if (offset + UsnNative.FileNotifyInformation.HeaderSize > buffer.Length) break;
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uint nextEntry = BinaryPrimitives.ReadUInt32LittleEndian(buffer[offset..]);
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uint action = BinaryPrimitives.ReadUInt32LittleEndian(buffer[(offset + 4)..]);
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int nameBytes = (int)BinaryPrimitives.ReadUInt32LittleEndian(buffer[(offset + 8)..]);
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int nameOffset = offset + UsnNative.FileNotifyInformation.HeaderSize;
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if (nameBytes <= 0 || nameOffset + nameBytes > buffer.Length) break;
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// 文件名是相对被监听目录（这里是卷根）的路径，形如 "Users\Public\x.txt"，不以 NUL 结尾
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var relative = MemoryMarshal.Cast<byte, char>(buffer.Slice(nameOffset, nameBytes));
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Handle(relative, action);
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if (nextEntry == 0) break;
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offset += (int)nextEntry;
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}
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}
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private void Handle(ReadOnlySpan<char> relative, uint action)
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{
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if (relative.Length == 0) return;
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var fullPath = string.Concat(_root, relative);
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switch (action)
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{
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case UsnNative.FILE_ACTION_ADDED:
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case UsnNative.FILE_ACTION_RENAMED_NEW_NAME:
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case UsnNative.FILE_ACTION_MODIFIED:
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UpsertFromDisk(fullPath);
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break;
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case UsnNative.FILE_ACTION_REMOVED:
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case UsnNative.FILE_ACTION_RENAMED_OLD_NAME:
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QueueDirectoryResync(fullPath);
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break;
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}
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}
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/// <summary>按路径 stat 出 FRN + 元数据，然后按 FRN 落入索引（存在则更新，不存在则新增）。</summary>
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private void UpsertFromDisk(string fullPath)
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{
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if (!UsnNative.TryStatPath(fullPath, out var info)) return; // 文件已再次消失等，忽略
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var name = Path.GetFileName(fullPath.AsSpan());
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if (name.Length == 0) return;
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ulong parentFrn = 0;
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var parentPath = Path.GetDirectoryName(fullPath);
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if (!string.IsNullOrEmpty(parentPath) && !parentPath.Equals(_root, StringComparison.OrdinalIgnoreCase))
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{
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parentFrn = GetDirectoryFrn(parentPath);
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}
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bool isDirectory = (info.FileAttributes & UsnNative.FILE_ATTRIBUTE_DIRECTORY) != 0;
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_index.UpsertFromFileSystem(
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info.FileIndex,
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parentFrn,
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name,
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isDirectory,
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isDirectory ? 0 : info.FileSize,
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UsnVolumeIndex.FileTimeToTicks(info.LastWriteTime.ToInt64()),
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info.FileAttributes);
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if (isDirectory) _directoryFrnCache[fullPath] = UsnNative.NormalizeFrn(info.FileIndex);
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}
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private ulong GetDirectoryFrn(string directoryPath)
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{
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if (_directoryFrnCache.TryGetValue(directoryPath, out var cached)) return cached;
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if (!UsnNative.TryStatPath(directoryPath, out var info)) return 0;
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var frn = UsnNative.NormalizeFrn(info.FileIndex);
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_directoryFrnCache[directoryPath] = frn;
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return frn;
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}
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private void QueueDirectoryResync(string fullPath)
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{
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var directory = Path.GetDirectoryName(fullPath);
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if (!string.IsNullOrEmpty(directory)) _pendingResync.Add(directory);
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}
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private void FlushPendingResync()
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{
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if (_pendingResync.Count == 0) return;
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_resyncScratch.Clear();
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foreach (var directory in _pendingResync)
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{
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_resyncScratch.Add(directory);
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if (_resyncScratch.Count >= MaxResyncDirectoriesPerPass) break;
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}
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int removed = 0;
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foreach (var directory in _resyncScratch)
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{
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_pendingResync.Remove(directory);
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removed += _index.ResyncDirectoryFromDisk(directory);
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}
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if (removed > 0) _index.ReportWatchIssue(null, removed);
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}
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}
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