mcs/class/System/System.IO/KeventWatcher.cs

   1 //
   2 // System.IO.KeventWatcher.cs: interface with osx kevent
   3 //
   4 // Authors:
   5 //      Geoff Norton (gnorton@customerdna.com)
   6 //      Cody Russell (cody@xamarin.com)
   7 //      Alexis Christoforides (lexas@xamarin.com)
   8 //
   9 // (c) 2004 Geoff Norton
  10 // Copyright 2014 Xamarin Inc
  11 //
  12 // Permission is hereby granted, free of charge, to any person obtaining
  13 // a copy of this software and associated documentation files (the
  14 // "Software"), to deal in the Software without restriction, including
  15 // without limitation the rights to use, copy, modify, merge, publish,
  16 // distribute, sublicense, and/or sell copies of the Software, and to
  17 // permit persons to whom the Software is furnished to do so, subject to
  18 // the following conditions:
  19 //
  20 // The above copyright notice and this permission notice shall be
  21 // included in all copies or substantial portions of the Software.
  22 //
  23 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  24 // EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  25 // MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  26 // NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
  27 // LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
  28 // OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
  29 // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  30 //
  31
  32 using System;
  33 using System.Collections;
  34 using System.Collections.Generic;
  35 using System.ComponentModel;
  36 using System.Runtime.CompilerServices;
  37 using System.Runtime.InteropServices;
  38 using System.Text;
  39 using System.Threading;
  40 using System.Reflection;
  41
  42 namespace System.IO {
  43
  44         [Flags]
  45         enum EventFlags : ushort {
  46                 Add         = 0x0001,
  47                 Delete      = 0x0002,
  48                 Enable      = 0x0004,
  49                 Disable     = 0x0008,
  50                 OneShot     = 0x0010,
  51                 Clear       = 0x0020,
  52                 Receipt     = 0x0040,
  53                 Dispatch    = 0x0080,
  54
  55                 Flag0       = 0x1000,
  56                 Flag1       = 0x2000,
  57                 SystemFlags = unchecked (0xf000),
  58
  59                 // Return values.
  60                 EOF         = 0x8000,
  61                 Error       = 0x4000,
  62         }
  63
  64         enum EventFilter : short {
  65                 Read = -1,
  66                 Write = -2,
  67                 Aio = -3,
  68                 Vnode = -4,
  69                 Proc = -5,
  70                 Signal = -6,
  71                 Timer = -7,
  72                 MachPort = -8,
  73                 FS = -9,
  74                 User = -10,
  75                 VM = -11
  76         }
  77
  78         [Flags]
  79         enum FilterFlags : uint {
  80                 ReadPoll          = EventFlags.Flag0,
  81                 ReadOutOfBand     = EventFlags.Flag1,
  82                 ReadLowWaterMark  = 0x00000001,
  83
  84                 WriteLowWaterMark = ReadLowWaterMark,
  85
  86                 NoteTrigger       = 0x01000000,
  87                 NoteFFNop         = 0x00000000,
  88                 NoteFFAnd         = 0x40000000,
  89                 NoteFFOr          = 0x80000000,
  90                 NoteFFCopy        = 0xc0000000,
  91                 NoteFFCtrlMask    = 0xc0000000,
  92                 NoteFFlagsMask    = 0x00ffffff,
  93
  94                 VNodeDelete       = 0x00000001,
  95                 VNodeWrite        = 0x00000002,
  96                 VNodeExtend       = 0x00000004,
  97                 VNodeAttrib       = 0x00000008,
  98                 VNodeLink         = 0x00000010,
  99                 VNodeRename       = 0x00000020,
 100                 VNodeRevoke       = 0x00000040,
 101                 VNodeNone         = 0x00000080,
 102
 103                 ProcExit          = 0x80000000,
 104                 ProcFork          = 0x40000000,
 105                 ProcExec          = 0x20000000,
 106                 ProcReap          = 0x10000000,
 107                 ProcSignal        = 0x08000000,
 108                 ProcExitStatus    = 0x04000000,
 109                 ProcResourceEnd   = 0x02000000,
 110
 111                 // iOS only
 112                 ProcAppactive     = 0x00800000,
 113                 ProcAppBackground = 0x00400000,
 114                 ProcAppNonUI      = 0x00200000,
 115                 ProcAppInactive   = 0x00100000,
 116                 ProcAppAllStates  = 0x00f00000,
 117
 118                 // Masks
 119                 ProcPDataMask     = 0x000fffff,
 120                 ProcControlMask   = 0xfff00000,
 121
 122                 VMPressure        = 0x80000000,
 123                 VMPressureTerminate = 0x40000000,
 124                 VMPressureSuddenTerminate = 0x20000000,
 125                 VMError           = 0x10000000,
 126                 TimerSeconds      =    0x00000001,
 127                 TimerMicroSeconds =   0x00000002,
 128                 TimerNanoSeconds  =   0x00000004,
 129                 TimerAbsolute     =   0x00000008,
 130         }
 131
 132         [StructLayout(LayoutKind.Sequential)]
 133         struct kevent : IDisposable {
 134                 public UIntPtr ident;
 135                 public EventFilter filter;
 136                 public EventFlags flags;
 137                 public FilterFlags fflags;
 138                 public IntPtr data;
 139                 public IntPtr udata;
 140
 141                 public void Dispose ()
 142                 {
 143                         if (udata != IntPtr.Zero)
 144                                 Marshal.FreeHGlobal (udata);
 145                 }
 146
 147
 148         }
 149
 150         [StructLayout(LayoutKind.Sequential)]
 151         struct timespec {
 152                 public IntPtr tv_sec;
 153                 public IntPtr tv_usec;
 154         }
 155
 156         class PathData
 157         {
 158                 public string Path;
 159                 public bool IsDirectory;
 160                 public int Fd;
 161         }
 162
 163         class KqueueMonitor : IDisposable
 164         {
 165                 public int Connection
 166                 {
 167                         get { return conn; }
 168                 }
 169
 170                 public KqueueMonitor (FileSystemWatcher fsw)
 171                 {
 172                         this.fsw = fsw;
 173                         this.conn = -1;
 174                 }
 175
 176                 public void Dispose ()
 177                 {
 178                         CleanUp ();
 179                 }
 180
 181                 public void Start ()
 182                 {
 183                         lock (stateLock) {
 184                                 if (started)
 185                                         return;
 186
 187                                 conn = kqueue ();
 188
 189                                 if (conn == -1)
 190                                         throw new IOException (String.Format (
 191                                                 "kqueue() error at init, error code = '{0}'", Marshal.GetLastWin32Error ()));
 192
 193                                 thread = new Thread (() => DoMonitor ());
 194                                 thread.IsBackground = true;
 195                                 thread.Start ();
 196
 197                                 startedEvent.WaitOne ();
 198
 199                                 if (exc != null) {
 200                                         thread.Join ();
 201                                         CleanUp ();
 202                                         throw exc;
 203                                 }
 204
 205                                 started = true;
 206                         }
 207                 }
 208
 209                 public void Stop ()
 210                 {
 211                         lock (stateLock) {
 212                                 if (!started)
 213                                         return;
 214
 215                                 requestStop = true;
 216
 217                                 if (inDispatch)
 218                                         return;
 219                                 if (!thread.Join (2000))
 220                                         thread.Abort ();
 221
 222                                 requestStop = false;
 223                                 started = false;
 224
 225                                 if (exc != null)
 226                                         throw exc;
 227                         }
 228                 }
 229
 230                 void CleanUp ()
 231                 {
 232                         if (conn != -1)
 233                                 close (conn);
 234
 235                         conn = -1;
 236
 237                         foreach (int fd in fdsDict.Keys)
 238                                 close (fd);
 239
 240                         fdsDict.Clear ();
 241                         pathsDict.Clear ();
 242                 }
 243
 244                 void DoMonitor ()
 245                 {
 246                         try {
 247                                 Setup ();
 248                         } catch (Exception e) {
 249                                 exc = e;
 250                         } finally {
 251                                 startedEvent.Set ();
 252                         }
 253
 254                         if (exc != null) {
 255                                 fsw.DispatchErrorEvents (new ErrorEventArgs (exc));
 256                                 return;
 257                         }
 258
 259                         try {
 260                                 Monitor ();
 261                         } catch (Exception e) {
 262                                 exc = e;
 263                         } finally {
 264                                 CleanUp ();
 265                                 if (!requestStop) { // failure
 266                                         started = false;
 267                                         inDispatch = false;
 268                                         fsw.EnableRaisingEvents = false;
 269                                         throw exc;
 270                                 }
 271                                 if (exc != null)
 272                                         fsw.DispatchErrorEvents (new ErrorEventArgs (exc));
 273                                 requestStop = false;
 274                         }
 275                 }
 276
 277                 void Setup ()
 278                 {
 279                         var initialFds = new List<int> ();
 280
 281                         // fsw.FullPath may end in '/', see https://bugzilla.xamarin.com/show_bug.cgi?id=5747
 282                         if (fsw.FullPath.EndsWith ("/", StringComparison.Ordinal))
 283                                 fullPathNoLastSlash = fsw.FullPath.Substring (0, fsw.FullPath.Length - 1);
 284                         else
 285                                 fullPathNoLastSlash = fsw.FullPath;
 286
 287                         // GetFilenameFromFd() returns the *realpath* which can be different than fsw.FullPath because symlinks.
 288                         // If so, introduce a fixup step.
 289                         int fd = open (fullPathNoLastSlash, O_EVTONLY, 0);
 290                         var resolvedFullPath = GetFilenameFromFd (fd);
 291                         close (fd);
 292
 293                         if (resolvedFullPath != fullPathNoLastSlash)
 294                                 fixupPath = resolvedFullPath;
 295                         else
 296                                 fixupPath = null;
 297
 298                         Scan (fullPathNoLastSlash, false, ref initialFds);
 299
 300                         var immediate_timeout = new timespec { tv_sec = (IntPtr)0, tv_usec = (IntPtr)0 };
 301                         var eventBuffer = new kevent[0]; // we don't want to take any events from the queue at this point
 302                         var changes = CreateChangeList (ref initialFds);
 303
 304                         int numEvents = kevent (conn, changes, changes.Length, eventBuffer, eventBuffer.Length, ref immediate_timeout);
 305
 306                         if (numEvents == -1) {
 307                                 var errMsg = String.Format ("kevent() error at initial event registration, error code = '{0}'", Marshal.GetLastWin32Error ());
 308                                 throw new IOException (errMsg);
 309                         }
 310                 }
 311
 312                 kevent[] CreateChangeList (ref List<int> FdList)
 313                 {
 314                         if (FdList.Count == 0)
 315                                 return emptyEventList;
 316
 317                         var changes = new List<kevent> ();
 318                         foreach (int fd in FdList) {
 319                                 var change = new kevent {
 320
 321                                         ident = (UIntPtr)fd,
 322                                         filter = EventFilter.Vnode,
 323                                         flags = EventFlags.Add | EventFlags.Enable | EventFlags.Clear,
 324                                         fflags = FilterFlags.VNodeDelete | FilterFlags.VNodeExtend |
 325                                                 FilterFlags.VNodeRename | FilterFlags.VNodeAttrib |
 326                                                 FilterFlags.VNodeLink | FilterFlags.VNodeRevoke |
 327                                                 FilterFlags.VNodeWrite,
 328                                         data = IntPtr.Zero,
 329                                         udata = IntPtr.Zero
 330                                 };
 331
 332                                 changes.Add (change);
 333                         }
 334                         FdList.Clear ();
 335
 336                         return changes.ToArray ();
 337                 }
 338
 339                 void Monitor ()
 340                 {
 341                         var timeout = new timespec { tv_sec = (IntPtr)0, tv_usec = (IntPtr)500000000 };
 342                         var eventBuffer = new kevent[32];
 343                         var newFds = new List<int> ();
 344                         List<PathData> removeQueue = new List<PathData> ();
 345                         List<string> rescanQueue = new List<string> ();
 346
 347                         int retries = 0;
 348
 349                         while (!requestStop) {
 350                                 var changes = CreateChangeList (ref newFds);
 351
 352                                 int numEvents = kevent (conn, changes, changes.Length, eventBuffer, eventBuffer.Length, ref timeout);
 353
 354                                 if (numEvents == -1) {
 355                                         if (++retries == 3)
 356                                                 throw new IOException (String.Format (
 357                                                         "persistent kevent() error, error code = '{0}'", Marshal.GetLastWin32Error ()));
 358
 359                                         continue;
 360                                 }
 361
 362                                 retries = 0;
 363
 364                                 for (var i = 0; i < numEvents; i++) {
 365                                         var kevt = eventBuffer [i];
 366                                         var pathData = fdsDict [(int)kevt.ident];
 367
 368                                         if ((kevt.flags & EventFlags.Error) == EventFlags.Error) {
 369                                                 var errMsg = String.Format ("kevent() error watching path '{0}', error code = '{1}'", pathData.Path, kevt.data);
 370                                                 fsw.DispatchErrorEvents (new ErrorEventArgs (new IOException (errMsg)));
 371                                                 continue;
 372                                         }
 373
 374                                         if ((kevt.fflags & FilterFlags.VNodeDelete) == FilterFlags.VNodeDelete || (kevt.fflags & FilterFlags.VNodeRevoke) == FilterFlags.VNodeRevoke) {
 375                                                 removeQueue.Add (pathData);
 376                                                 continue;
 377                                         }
 378
 379                                         if ((kevt.fflags & FilterFlags.VNodeRename) == FilterFlags.VNodeRename) {
 380                                                         UpdatePath (pathData);
 381                                         }
 382
 383                                         if ((kevt.fflags & FilterFlags.VNodeWrite) == FilterFlags.VNodeWrite) {
 384                                                 if (pathData.IsDirectory) //TODO: Check if dirs trigger Changed events on .NET
 385                                                         rescanQueue.Add (pathData.Path);
 386                                                 else
 387                                                         PostEvent (FileAction.Modified, pathData.Path);
 388                                         }
 389
 390                                         if ((kevt.fflags & FilterFlags.VNodeAttrib) == FilterFlags.VNodeAttrib || (kevt.fflags & FilterFlags.VNodeExtend) == FilterFlags.VNodeExtend)
 391                                                 PostEvent (FileAction.Modified, pathData.Path);
 392                                 }
 393
 394                                 removeQueue.ForEach (Remove);
 395                                 removeQueue.Clear ();
 396
 397                                 rescanQueue.ForEach (path => {
 398                                         Scan (path, true, ref newFds);
 399                                 });
 400                                 rescanQueue.Clear ();
 401                         }
 402                 }
 403
 404                 PathData Add (string path, bool postEvents, ref List<int> fds)
 405                 {
 406                         PathData pathData;
 407                         pathsDict.TryGetValue (path, out pathData);
 408
 409                         if (pathData != null)
 410                                 return pathData;
 411
 412                         if (fdsDict.Count >= maxFds)
 413                                 throw new IOException ("kqueue() FileSystemWatcher has reached the maximum nunmber of files to watch.");
 414
 415                         var fd = open (path, O_EVTONLY, 0);
 416
 417                         if (fd == -1) {
 418                                 fsw.DispatchErrorEvents (new ErrorEventArgs (new IOException (String.Format (
 419                                         "open() error while attempting to process path '{0}', error code = '{1}'", path, Marshal.GetLastWin32Error ()))));
 420                                 return null;
 421                         }
 422
 423                         try {
 424                                 fds.Add (fd);
 425
 426                                 var attrs = File.GetAttributes (path);
 427
 428                                 pathData = new PathData {
 429                                         Path = path,
 430                                         Fd = fd,
 431                                         IsDirectory = (attrs & FileAttributes.Directory) == FileAttributes.Directory
 432                                 };
 433
 434                                 pathsDict.Add (path, pathData);
 435                                 fdsDict.Add (fd, pathData);
 436
 437                                 if (postEvents)
 438                                         PostEvent (FileAction.Added, path);
 439
 440                                 return pathData;
 441                         } catch (Exception e) {
 442                                 close (fd);
 443                                 fsw.DispatchErrorEvents (new ErrorEventArgs (e));
 444                                 return null;
 445                         }
 446
 447                 }
 448
 449                 void Remove (PathData pathData)
 450                 {
 451                         fdsDict.Remove (pathData.Fd);
 452                         pathsDict.Remove (pathData.Path);
 453                         close (pathData.Fd);
 454                         PostEvent (FileAction.Removed, pathData.Path);
 455                 }
 456
 457                 void RemoveTree (PathData pathData)
 458                 {
 459                         var toRemove = new List<PathData> ();
 460
 461                         toRemove.Add (pathData);
 462
 463                         if (pathData.IsDirectory) {
 464                                 var prefix = pathData.Path + Path.DirectorySeparatorChar;
 465                                 foreach (var path in pathsDict.Keys)
 466                                         if (path.StartsWith (prefix)) {
 467                                                 toRemove.Add (pathsDict [path]);
 468                                         }
 469                         }
 470                         toRemove.ForEach (Remove);
 471                 }
 472
 473                 void UpdatePath (PathData pathData)
 474                 {
 475                         var newRoot = GetFilenameFromFd (pathData.Fd);
 476                         if (!newRoot.StartsWith (fullPathNoLastSlash)) { // moved outside of our watched path (so stop observing it)
 477                                 RemoveTree (pathData);
 478                                 return;
 479                         }
 480
 481                         var toRename = new List<PathData> ();
 482                         var oldRoot = pathData.Path;
 483
 484                         toRename.Add (pathData);
 485
 486                         if (pathData.IsDirectory) { // anything under the directory must have their paths updated
 487                                 var prefix = oldRoot + Path.DirectorySeparatorChar;
 488                                 foreach (var path in pathsDict.Keys)
 489                                         if (path.StartsWith (prefix))
 490                                                 toRename.Add (pathsDict [path]);
 491                         }
 492
 493                         foreach (var renaming in toRename) {
 494                                 var oldPath = renaming.Path;
 495                                 var newPath = newRoot + oldPath.Substring (oldRoot.Length);
 496
 497                                 renaming.Path = newPath;
 498                                 pathsDict.Remove (oldPath);
 499
 500                                 // destination may exist in our records from a Created event, take care of it
 501                                 if (pathsDict.ContainsKey (newPath)) {
 502                                         var conflict = pathsDict [newPath];
 503                                         if (GetFilenameFromFd (renaming.Fd) == GetFilenameFromFd (conflict.Fd))
 504                                                 Remove (conflict);
 505                                         else
 506                                                 UpdatePath (conflict);
 507                                 }
 508
 509                                 pathsDict.Add (newPath, renaming);
 510                         }
 511
 512                         PostEvent (FileAction.RenamedNewName, oldRoot, newRoot);
 513                 }
 514
 515                 void Scan (string path, bool postEvents, ref List<int> fds)
 516                 {
 517                         if (requestStop)
 518                                 return;
 519
 520                         var pathData = Add (path, postEvents, ref fds);
 521
 522                         if (pathData == null)
 523                                 return;
 524
 525                         if (!pathData.IsDirectory)
 526                                 return;
 527
 528                         var dirsToProcess = new List<string> ();
 529                         dirsToProcess.Add (path);
 530
 531                         while (dirsToProcess.Count > 0) {
 532                                 var tmp = dirsToProcess [0];
 533                                 dirsToProcess.RemoveAt (0);
 534
 535                                 var info = new DirectoryInfo (tmp);
 536                                 FileSystemInfo[] fsInfos = null;
 537                                 try {
 538                                         fsInfos = info.GetFileSystemInfos ();
 539
 540                                 } catch (IOException) {
 541                                         // this can happen if the directory has been deleted already.
 542                                         // that's okay, just keep processing the other dirs.
 543                                         fsInfos = new FileSystemInfo[0];
 544                                 }
 545
 546                                 foreach (var fsi in fsInfos) {
 547                                         if ((fsi.Attributes & FileAttributes.Directory) == FileAttributes.Directory && !fsw.IncludeSubdirectories)
 548                                                 continue;
 549
 550                                         if ((fsi.Attributes & FileAttributes.Directory) != FileAttributes.Directory && !fsw.Pattern.IsMatch (fsi.FullName))
 551                                                 continue;
 552
 553                                         var currentPathData = Add (fsi.FullName, postEvents, ref fds);
 554
 555                                         if (currentPathData != null && currentPathData.IsDirectory)
 556                                                 dirsToProcess.Add (fsi.FullName);
 557                                 }
 558                         }
 559                 }
 560
 561                 void PostEvent (FileAction action, string path, string newPath = null)
 562                 {
 563                         RenamedEventArgs renamed = null;
 564
 565                         if (requestStop || action == 0)
 566                                 return;
 567
 568                         // e.Name
 569                         string name = path.Substring (fullPathNoLastSlash.Length + 1);
 570
 571                         // only post events that match filter pattern. check both old and new paths for renames
 572                         if (!fsw.Pattern.IsMatch (path) && (newPath == null || !fsw.Pattern.IsMatch (newPath)))
 573                                 return;
 574
 575                         if (action == FileAction.RenamedNewName) {
 576                                 string newName = newPath.Substring (fullPathNoLastSlash.Length + 1);
 577                                 renamed = new RenamedEventArgs (WatcherChangeTypes.Renamed, fsw.Path, newName, name);
 578                         }
 579
 580                         fsw.DispatchEvents (action, name, ref renamed);
 581
 582                         if (fsw.Waiting) {
 583                                 lock (fsw) {
 584                                         fsw.Waiting = false;
 585                                         System.Threading.Monitor.PulseAll (fsw);
 586                                 }
 587                         }
 588                 }
 589
 590                 private string GetFilenameFromFd (int fd)
 591                 {
 592                         var sb = new StringBuilder (__DARWIN_MAXPATHLEN);
 593
 594                         if (fcntl (fd, F_GETPATH, sb) != -1) {
 595                                 if (fixupPath != null)
 596                                         sb.Replace (fixupPath, fullPathNoLastSlash, 0, fixupPath.Length); // see Setup()
 597
 598                                 return sb.ToString ();
 599                         } else {
 600                                 fsw.DispatchErrorEvents (new ErrorEventArgs (new IOException (String.Format (
 601                                         "fcntl() error while attempting to get path for fd '{0}', error code = '{1}'", fd, Marshal.GetLastWin32Error ()))));
 602                                 return String.Empty;
 603                         }
 604                 }
 605
 606                 const int O_EVTONLY = 0x8000;
 607                 const int F_GETPATH = 50;
 608                 const int __DARWIN_MAXPATHLEN = 1024;
 609                 static readonly kevent[] emptyEventList = new System.IO.kevent[0];
 610                 const int maxFds = 200;
 611
 612                 FileSystemWatcher fsw;
 613                 int conn;
 614                 Thread thread;
 615                 volatile bool requestStop = false;
 616                 AutoResetEvent startedEvent = new AutoResetEvent (false);
 617                 bool started = false;
 618                 bool inDispatch = false;
 619                 Exception exc = null;
 620                 object stateLock = new object ();
 621
 622                 readonly Dictionary<string, PathData> pathsDict = new Dictionary<string, PathData> ();
 623                 readonly Dictionary<int, PathData> fdsDict = new Dictionary<int, PathData> ();
 624                 string fixupPath = null;
 625                 string fullPathNoLastSlash = null;
 626
 627                 [DllImport ("libc", EntryPoint="fcntl", CharSet=CharSet.Auto, SetLastError=true)]
 628                 static extern int fcntl (int file_names_by_descriptor, int cmd, StringBuilder sb);
 629
 630                 [DllImport ("libc")]
 631                 extern static int open (string path, int flags, int mode_t);
 632
 633                 [DllImport ("libc")]
 634                 extern static int close (int fd);
 635
 636                 [DllImport ("libc")]
 637                 extern static int kqueue ();
 638
 639                 [DllImport ("libc")]
 640                 extern static int kevent (int kq, [In]kevent[] ev, int nchanges, [Out]kevent[] evtlist, int nevents, [In] ref timespec time);
 641         }
 642
 643         class KeventWatcher : IFileWatcher
 644         {
 645                 static bool failed;
 646                 static KeventWatcher instance;
 647                 static Hashtable watches;  // <FileSystemWatcher, KqueueMonitor>
 648
 649                 private KeventWatcher ()
 650                 {
 651                 }
 652
 653                 // Locked by caller
 654                 public static bool GetInstance (out IFileWatcher watcher)
 655                 {
 656                         if (failed == true) {
 657                                 watcher = null;
 658                                 return false;
 659                         }
 660
 661                         if (instance != null) {
 662                                 watcher = instance;
 663                                 return true;
 664                         }
 665
 666                         watches = Hashtable.Synchronized (new Hashtable ());
 667                         var conn = kqueue();
 668                         if (conn == -1) {
 669                                 failed = true;
 670                                 watcher = null;
 671                                 return false;
 672                         }
 673                         close (conn);
 674
 675                         instance = new KeventWatcher ();
 676                         watcher = instance;
 677                         return true;
 678                 }
 679
 680                 public void StartDispatching (FileSystemWatcher fsw)
 681                 {
 682                         KqueueMonitor monitor;
 683
 684                         if (watches.ContainsKey (fsw)) {
 685                                 monitor = (KqueueMonitor)watches [fsw];
 686                         } else {
 687                                 monitor = new KqueueMonitor (fsw);
 688                                 watches.Add (fsw, monitor);
 689                         }
 690
 691                         monitor.Start ();
 692                 }
 693
 694                 public void StopDispatching (FileSystemWatcher fsw)
 695                 {
 696                         KqueueMonitor monitor = (KqueueMonitor)watches [fsw];
 697                         if (monitor == null)
 698                                 return;
 699
 700                         monitor.Stop ();
 701                 }
 702
 703                 [DllImport ("libc")]
 704                 extern static int close (int fd);
 705
 706                 [DllImport ("libc")]
 707                 extern static int kqueue ();
 708         }
 709 }
 710