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                                 // This will break the wait in Monitor ()
 220                                 lock (connLock) {
 221                                         if (conn != -1)
 222                                                 close (conn);
 223                                         conn = -1;
 224                                 }
 225
 226                                 if (!thread.Join (2000))
 227                                         thread.Abort ();
 228
 229                                 requestStop = false;
 230                                 started = false;
 231
 232                                 if (exc != null)
 233                                         throw exc;
 234                         }
 235                 }
 236
 237                 void CleanUp ()
 238                 {
 239                         lock (connLock) {
 240                                 if (conn != -1)
 241                                         close (conn);
 242                                 conn = -1;
 243                         }
 244
 245                         foreach (int fd in fdsDict.Keys)
 246                                 close (fd);
 247
 248                         fdsDict.Clear ();
 249                         pathsDict.Clear ();
 250                 }
 251
 252                 void DoMonitor ()
 253                 {
 254                         try {
 255                                 Setup ();
 256                         } catch (Exception e) {
 257                                 exc = e;
 258                         } finally {
 259                                 startedEvent.Set ();
 260                         }
 261
 262                         if (exc != null) {
 263                                 fsw.DispatchErrorEvents (new ErrorEventArgs (exc));
 264                                 return;
 265                         }
 266
 267                         try {
 268                                 Monitor ();
 269                         } catch (Exception e) {
 270                                 exc = e;
 271                         } finally {
 272                                 CleanUp ();
 273                                 if (!requestStop) { // failure
 274                                         started = false;
 275                                         inDispatch = false;
 276                                         fsw.EnableRaisingEvents = false;
 277                                         throw exc;
 278                                 }
 279                                 if (exc != null)
 280                                         fsw.DispatchErrorEvents (new ErrorEventArgs (exc));
 281                                 requestStop = false;
 282                         }
 283                 }
 284
 285                 void Setup ()
 286                 {
 287                         var initialFds = new List<int> ();
 288
 289                         // fsw.FullPath may end in '/', see https://bugzilla.xamarin.com/show_bug.cgi?id=5747
 290                         if (fsw.FullPath != "/" && fsw.FullPath.EndsWith ("/", StringComparison.Ordinal))
 291                                 fullPathNoLastSlash = fsw.FullPath.Substring (0, fsw.FullPath.Length - 1);
 292                         else
 293                                 fullPathNoLastSlash = fsw.FullPath;
 294
 295                         // GetFilenameFromFd() returns the *realpath* which can be different than fsw.FullPath because symlinks.
 296                         // If so, introduce a fixup step.
 297                         int fd = open (fullPathNoLastSlash, O_EVTONLY, 0);
 298                         var resolvedFullPath = GetFilenameFromFd (fd);
 299                         close (fd);
 300
 301                         if (resolvedFullPath != fullPathNoLastSlash)
 302                                 fixupPath = resolvedFullPath;
 303                         else
 304                                 fixupPath = null;
 305
 306                         Scan (fullPathNoLastSlash, false, ref initialFds);
 307
 308                         var immediate_timeout = new timespec { tv_sec = (IntPtr)0, tv_usec = (IntPtr)0 };
 309                         var eventBuffer = new kevent[0]; // we don't want to take any events from the queue at this point
 310                         var changes = CreateChangeList (ref initialFds);
 311
 312                         int numEvents = kevent (conn, changes, changes.Length, eventBuffer, eventBuffer.Length, ref immediate_timeout);
 313
 314                         if (numEvents == -1) {
 315                                 var errMsg = String.Format ("kevent() error at initial event registration, error code = '{0}'", Marshal.GetLastWin32Error ());
 316                                 throw new IOException (errMsg);
 317                         }
 318                 }
 319
 320                 kevent[] CreateChangeList (ref List<int> FdList)
 321                 {
 322                         if (FdList.Count == 0)
 323                                 return emptyEventList;
 324
 325                         var changes = new List<kevent> ();
 326                         foreach (int fd in FdList) {
 327                                 var change = new kevent {
 328
 329                                         ident = (UIntPtr)fd,
 330                                         filter = EventFilter.Vnode,
 331                                         flags = EventFlags.Add | EventFlags.Enable | EventFlags.Clear,
 332                                         fflags = FilterFlags.VNodeDelete | FilterFlags.VNodeExtend |
 333                                                 FilterFlags.VNodeRename | FilterFlags.VNodeAttrib |
 334                                                 FilterFlags.VNodeLink | FilterFlags.VNodeRevoke |
 335                                                 FilterFlags.VNodeWrite,
 336                                         data = IntPtr.Zero,
 337                                         udata = IntPtr.Zero
 338                                 };
 339
 340                                 changes.Add (change);
 341                         }
 342                         FdList.Clear ();
 343
 344                         return changes.ToArray ();
 345                 }
 346
 347                 void Monitor ()
 348                 {
 349                         var eventBuffer = new kevent[32];
 350                         var newFds = new List<int> ();
 351                         List<PathData> removeQueue = new List<PathData> ();
 352                         List<string> rescanQueue = new List<string> ();
 353
 354                         int retries = 0;
 355
 356                         while (!requestStop) {
 357                                 var changes = CreateChangeList (ref newFds);
 358
 359                                 int numEvents = kevent_notimeout (conn, changes, changes.Length, eventBuffer, eventBuffer.Length, IntPtr.Zero);
 360
 361                                 if (numEvents == -1) {
 362                                         // Stop () signals us to stop by closing the connection
 363                                         if (requestStop)
 364                                                 break;
 365                                         if (++retries == 3)
 366                                                 throw new IOException (String.Format (
 367                                                         "persistent kevent() error, error code = '{0}'", Marshal.GetLastWin32Error ()));
 368
 369                                         continue;
 370                                 }
 371
 372                                 retries = 0;
 373
 374                                 for (var i = 0; i < numEvents; i++) {
 375                                         var kevt = eventBuffer [i];
 376                                         var pathData = fdsDict [(int)kevt.ident];
 377
 378                                         if ((kevt.flags & EventFlags.Error) == EventFlags.Error) {
 379                                                 var errMsg = String.Format ("kevent() error watching path '{0}', error code = '{1}'", pathData.Path, kevt.data);
 380                                                 fsw.DispatchErrorEvents (new ErrorEventArgs (new IOException (errMsg)));
 381                                                 continue;
 382                                         }
 383
 384                                         if ((kevt.fflags & FilterFlags.VNodeDelete) == FilterFlags.VNodeDelete || (kevt.fflags & FilterFlags.VNodeRevoke) == FilterFlags.VNodeRevoke) {
 385                                                 removeQueue.Add (pathData);
 386                                                 continue;
 387                                         }
 388
 389                                         if ((kevt.fflags & FilterFlags.VNodeRename) == FilterFlags.VNodeRename) {
 390                                                         UpdatePath (pathData);
 391                                         }
 392
 393                                         if ((kevt.fflags & FilterFlags.VNodeWrite) == FilterFlags.VNodeWrite) {
 394                                                 if (pathData.IsDirectory) //TODO: Check if dirs trigger Changed events on .NET
 395                                                         rescanQueue.Add (pathData.Path);
 396                                                 else
 397                                                         PostEvent (FileAction.Modified, pathData.Path);
 398                                         }
 399
 400                                         if ((kevt.fflags & FilterFlags.VNodeAttrib) == FilterFlags.VNodeAttrib || (kevt.fflags & FilterFlags.VNodeExtend) == FilterFlags.VNodeExtend)
 401                                                 PostEvent (FileAction.Modified, pathData.Path);
 402                                 }
 403
 404                                 removeQueue.ForEach (Remove);
 405                                 removeQueue.Clear ();
 406
 407                                 rescanQueue.ForEach (path => {
 408                                         Scan (path, true, ref newFds);
 409                                 });
 410                                 rescanQueue.Clear ();
 411                         }
 412                 }
 413
 414                 PathData Add (string path, bool postEvents, ref List<int> fds)
 415                 {
 416                         PathData pathData;
 417                         pathsDict.TryGetValue (path, out pathData);
 418
 419                         if (pathData != null)
 420                                 return pathData;
 421
 422                         if (fdsDict.Count >= maxFds)
 423                                 throw new IOException ("kqueue() FileSystemWatcher has reached the maximum nunmber of files to watch.");
 424
 425                         var fd = open (path, O_EVTONLY, 0);
 426
 427                         if (fd == -1) {
 428                                 fsw.DispatchErrorEvents (new ErrorEventArgs (new IOException (String.Format (
 429                                         "open() error while attempting to process path '{0}', error code = '{1}'", path, Marshal.GetLastWin32Error ()))));
 430                                 return null;
 431                         }
 432
 433                         try {
 434                                 fds.Add (fd);
 435
 436                                 var attrs = File.GetAttributes (path);
 437
 438                                 pathData = new PathData {
 439                                         Path = path,
 440                                         Fd = fd,
 441                                         IsDirectory = (attrs & FileAttributes.Directory) == FileAttributes.Directory
 442                                 };
 443
 444                                 pathsDict.Add (path, pathData);
 445                                 fdsDict.Add (fd, pathData);
 446
 447                                 if (postEvents)
 448                                         PostEvent (FileAction.Added, path);
 449
 450                                 return pathData;
 451                         } catch (Exception e) {
 452                                 close (fd);
 453                                 fsw.DispatchErrorEvents (new ErrorEventArgs (e));
 454                                 return null;
 455                         }
 456
 457                 }
 458
 459                 void Remove (PathData pathData)
 460                 {
 461                         fdsDict.Remove (pathData.Fd);
 462                         pathsDict.Remove (pathData.Path);
 463                         close (pathData.Fd);
 464                         PostEvent (FileAction.Removed, pathData.Path);
 465                 }
 466
 467                 void RemoveTree (PathData pathData)
 468                 {
 469                         var toRemove = new List<PathData> ();
 470
 471                         toRemove.Add (pathData);
 472
 473                         if (pathData.IsDirectory) {
 474                                 var prefix = pathData.Path + Path.DirectorySeparatorChar;
 475                                 foreach (var path in pathsDict.Keys)
 476                                         if (path.StartsWith (prefix)) {
 477                                                 toRemove.Add (pathsDict [path]);
 478                                         }
 479                         }
 480                         toRemove.ForEach (Remove);
 481                 }
 482
 483                 void UpdatePath (PathData pathData)
 484                 {
 485                         var newRoot = GetFilenameFromFd (pathData.Fd);
 486                         if (!newRoot.StartsWith (fullPathNoLastSlash)) { // moved outside of our watched path (so stop observing it)
 487                                 RemoveTree (pathData);
 488                                 return;
 489                         }
 490
 491                         var toRename = new List<PathData> ();
 492                         var oldRoot = pathData.Path;
 493
 494                         toRename.Add (pathData);
 495
 496                         if (pathData.IsDirectory) { // anything under the directory must have their paths updated
 497                                 var prefix = oldRoot + Path.DirectorySeparatorChar;
 498                                 foreach (var path in pathsDict.Keys)
 499                                         if (path.StartsWith (prefix))
 500                                                 toRename.Add (pathsDict [path]);
 501                         }
 502
 503                         foreach (var renaming in toRename) {
 504                                 var oldPath = renaming.Path;
 505                                 var newPath = newRoot + oldPath.Substring (oldRoot.Length);
 506
 507                                 renaming.Path = newPath;
 508                                 pathsDict.Remove (oldPath);
 509
 510                                 // destination may exist in our records from a Created event, take care of it
 511                                 if (pathsDict.ContainsKey (newPath)) {
 512                                         var conflict = pathsDict [newPath];
 513                                         if (GetFilenameFromFd (renaming.Fd) == GetFilenameFromFd (conflict.Fd))
 514                                                 Remove (conflict);
 515                                         else
 516                                                 UpdatePath (conflict);
 517                                 }
 518
 519                                 pathsDict.Add (newPath, renaming);
 520                         }
 521
 522                         PostEvent (FileAction.RenamedNewName, oldRoot, newRoot);
 523                 }
 524
 525                 void Scan (string path, bool postEvents, ref List<int> fds)
 526                 {
 527                         if (requestStop)
 528                                 return;
 529
 530                         var pathData = Add (path, postEvents, ref fds);
 531
 532                         if (pathData == null)
 533                                 return;
 534
 535                         if (!pathData.IsDirectory)
 536                                 return;
 537
 538                         var dirsToProcess = new List<string> ();
 539                         dirsToProcess.Add (path);
 540
 541                         while (dirsToProcess.Count > 0) {
 542                                 var tmp = dirsToProcess [0];
 543                                 dirsToProcess.RemoveAt (0);
 544
 545                                 var info = new DirectoryInfo (tmp);
 546                                 FileSystemInfo[] fsInfos = null;
 547                                 try {
 548                                         fsInfos = info.GetFileSystemInfos ();
 549
 550                                 } catch (IOException) {
 551                                         // this can happen if the directory has been deleted already.
 552                                         // that's okay, just keep processing the other dirs.
 553                                         fsInfos = new FileSystemInfo[0];
 554                                 }
 555
 556                                 foreach (var fsi in fsInfos) {
 557                                         if ((fsi.Attributes & FileAttributes.Directory) == FileAttributes.Directory && !fsw.IncludeSubdirectories)
 558                                                 continue;
 559
 560                                         if ((fsi.Attributes & FileAttributes.Directory) != FileAttributes.Directory && !fsw.Pattern.IsMatch (fsi.FullName))
 561                                                 continue;
 562
 563                                         var currentPathData = Add (fsi.FullName, postEvents, ref fds);
 564
 565                                         if (currentPathData != null && currentPathData.IsDirectory)
 566                                                 dirsToProcess.Add (fsi.FullName);
 567                                 }
 568                         }
 569                 }
 570
 571                 void PostEvent (FileAction action, string path, string newPath = null)
 572                 {
 573                         RenamedEventArgs renamed = null;
 574
 575                         if (requestStop || action == 0)
 576                                 return;
 577
 578                         // e.Name
 579                         string name = path.Substring (fullPathNoLastSlash.Length + 1);
 580
 581                         // only post events that match filter pattern. check both old and new paths for renames
 582                         if (!fsw.Pattern.IsMatch (path) && (newPath == null || !fsw.Pattern.IsMatch (newPath)))
 583                                 return;
 584
 585                         if (action == FileAction.RenamedNewName) {
 586                                 string newName = newPath.Substring (fullPathNoLastSlash.Length + 1);
 587                                 renamed = new RenamedEventArgs (WatcherChangeTypes.Renamed, fsw.Path, newName, name);
 588                         }
 589
 590                         fsw.DispatchEvents (action, name, ref renamed);
 591
 592                         if (fsw.Waiting) {
 593                                 lock (fsw) {
 594                                         fsw.Waiting = false;
 595                                         System.Threading.Monitor.PulseAll (fsw);
 596                                 }
 597                         }
 598                 }
 599
 600                 private string GetFilenameFromFd (int fd)
 601                 {
 602                         var sb = new StringBuilder (__DARWIN_MAXPATHLEN);
 603
 604                         if (fcntl (fd, F_GETPATH, sb) != -1) {
 605                                 if (fixupPath != null)
 606                                         sb.Replace (fixupPath, fullPathNoLastSlash, 0, fixupPath.Length); // see Setup()
 607
 608                                 return sb.ToString ();
 609                         } else {
 610                                 fsw.DispatchErrorEvents (new ErrorEventArgs (new IOException (String.Format (
 611                                         "fcntl() error while attempting to get path for fd '{0}', error code = '{1}'", fd, Marshal.GetLastWin32Error ()))));
 612                                 return String.Empty;
 613                         }
 614                 }
 615
 616                 const int O_EVTONLY = 0x8000;
 617                 const int F_GETPATH = 50;
 618                 const int __DARWIN_MAXPATHLEN = 1024;
 619                 static readonly kevent[] emptyEventList = new System.IO.kevent[0];
 620                 const int maxFds = 200;
 621
 622                 FileSystemWatcher fsw;
 623                 int conn;
 624                 Thread thread;
 625                 volatile bool requestStop = false;
 626                 AutoResetEvent startedEvent = new AutoResetEvent (false);
 627                 bool started = false;
 628                 bool inDispatch = false;
 629                 Exception exc = null;
 630                 object stateLock = new object ();
 631                 object connLock = new object ();
 632
 633                 readonly Dictionary<string, PathData> pathsDict = new Dictionary<string, PathData> ();
 634                 readonly Dictionary<int, PathData> fdsDict = new Dictionary<int, PathData> ();
 635                 string fixupPath = null;
 636                 string fullPathNoLastSlash = null;
 637
 638                 [DllImport ("libc", EntryPoint="fcntl", CharSet=CharSet.Auto, SetLastError=true)]
 639                 static extern int fcntl (int file_names_by_descriptor, int cmd, StringBuilder sb);
 640
 641                 [DllImport ("libc")]
 642                 extern static int open (string path, int flags, int mode_t);
 643
 644                 [DllImport ("libc")]
 645                 extern static int close (int fd);
 646
 647                 [DllImport ("libc")]
 648                 extern static int kqueue ();
 649
 650                 [DllImport ("libc")]
 651                 extern static int kevent (int kq, [In]kevent[] ev, int nchanges, [Out]kevent[] evtlist, int nevents, [In] ref timespec time);
 652
 653                 [DllImport ("libc", EntryPoint="kevent")]
 654                 extern static int kevent_notimeout (int kq, [In]kevent[] ev, int nchanges, [Out]kevent[] evtlist, int nevents, IntPtr ptr);
 655         }
 656
 657         class KeventWatcher : IFileWatcher
 658         {
 659                 static bool failed;
 660                 static KeventWatcher instance;
 661                 static Hashtable watches;  // <FileSystemWatcher, KqueueMonitor>
 662
 663                 private KeventWatcher ()
 664                 {
 665                 }
 666
 667                 // Locked by caller
 668                 public static bool GetInstance (out IFileWatcher watcher)
 669                 {
 670                         if (failed == true) {
 671                                 watcher = null;
 672                                 return false;
 673                         }
 674
 675                         if (instance != null) {
 676                                 watcher = instance;
 677                                 return true;
 678                         }
 679
 680                         watches = Hashtable.Synchronized (new Hashtable ());
 681                         var conn = kqueue();
 682                         if (conn == -1) {
 683                                 failed = true;
 684                                 watcher = null;
 685                                 return false;
 686                         }
 687                         close (conn);
 688
 689                         instance = new KeventWatcher ();
 690                         watcher = instance;
 691                         return true;
 692                 }
 693
 694                 public void StartDispatching (FileSystemWatcher fsw)
 695                 {
 696                         KqueueMonitor monitor;
 697
 698                         if (watches.ContainsKey (fsw)) {
 699                                 monitor = (KqueueMonitor)watches [fsw];
 700                         } else {
 701                                 monitor = new KqueueMonitor (fsw);
 702                                 watches.Add (fsw, monitor);
 703                         }
 704
 705                         monitor.Start ();
 706                 }
 707
 708                 public void StopDispatching (FileSystemWatcher fsw)
 709                 {
 710                         KqueueMonitor monitor = (KqueueMonitor)watches [fsw];
 711                         if (monitor == null)
 712                                 return;
 713
 714                         monitor.Stop ();
 715                 }
 716
 717                 [DllImport ("libc")]
 718                 extern static int close (int fd);
 719
 720                 [DllImport ("libc")]
 721                 extern static int kqueue ();
 722         }
 723 }
 724