src/w32notify.c

   1 /* Filesystem notifications support for GNU Emacs on the Microsoft Windows API.
   2    Copyright (C) 2012-2014 Free Software Foundation, Inc.
   3
   4 This file is part of GNU Emacs.
   5
   6 GNU Emacs is free software: you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation, either version 3 of the License, or
   9 (at your option) any later version.
  10
  11 GNU Emacs is distributed in the hope that it will be useful,
  12 but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 GNU General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
  18
  19 /* Written by Eli Zaretskii <eliz@gnu.org>.
  20
  21    Design overview:
  22
  23    For each watch request, we launch a separate worker thread.  The
  24    worker thread runs the watch_worker function, which issues an
  25    asynchronous call to ReadDirectoryChangesW, and then waits in
  26    SleepEx for that call to complete.  Waiting in SleepEx puts the
  27    thread in an "alertable" state, so it wakes up when either (a) the
  28    call to ReadDirectoryChangesW completes, or (b) the main thread
  29    instructs the worker thread to terminate by sending it an APC, see
  30    below.
  31
  32    When the ReadDirectoryChangesW call completes, its completion
  33    routine watch_completion is automatically called.  watch_completion
  34    stashes the received file events in a buffer used to communicate
  35    them to the main thread (using a critical section, so that several
  36    threads could use the same buffer), posts a special message,
  37    WM_EMACS_FILENOTIFY, to the Emacs's message queue, and returns.
  38    That causes the SleepEx function call inside watch_worker to
  39    return, and watch_worker then issues another call to
  40    ReadDirectoryChangesW.  (Except when it does not, see below.)
  41
  42    In a GUI session, the WM_EMACS_FILENOTIFY message posted to the
  43    message queue gets dispatched to the main Emacs window procedure,
  44    which queues it for processing by w32_read_socket.  When
  45    w32_read_socket sees this message, it accesses the buffer with file
  46    notifications (using a critical section), extracts the information,
  47    converts it to a series of FILE_NOTIFY_EVENT events, and stuffs
  48    them into the input event queue to be processed by keyboard.c input
  49    machinery (read_char via a call to kbd_buffer_get_event).
  50
  51    In a non-GUI session, we send the WM_EMACS_FILENOTIFY message to
  52    the main (a.k.a. "Lisp") thread instead, since there are no window
  53    procedures in console programs.  That message wakes up
  54    MsgWaitForMultipleObjects inside sys_select, which then signals to
  55    its caller that some keyboard input is available.  This causes
  56    w32_console_read_socket to be called, which accesses the buffer
  57    with file notifications and stuffs them into the input event queue
  58    for keyboard.c to process.
  59
  60    When the FILE_NOTIFY_EVENT event is processed by keyboard.c's
  61    kbd_buffer_get_event, it is converted to a Lispy event that can be
  62    bound to a command.  The default binding is file-notify-handle-event,
  63    defined on subr.el.
  64
  65    After w32_read_socket or w32_console_read_socket are done
  66    processing the notifications, they reset a flag signaling to all
  67    watch worker threads that the notifications buffer is available for
  68    more input.
  69
  70    When the watch is removed by a call to w32notify-rm-watch, the main
  71    thread requests that the worker thread terminates by queuing an APC
  72    for the worker thread.  The APC specifies the watch_end function to
  73    be called.  watch_end calls CancelIo on the outstanding
  74    ReadDirectoryChangesW call and closes the handle on which the
  75    watched directory was open.  When watch_end returns, the
  76    watch_completion function is called one last time with the
  77    ERROR_OPERATION_ABORTED status, which causes it to clean up and set
  78    a flag telling watch_worker to exit without issuing another
  79    ReadDirectoryChangesW call.  Since watch_worker is the thread
  80    procedure of the worker thread, exiting it causes the thread to
  81    exit.  The main thread waits for some time for the worker thread to
  82    exit, and if it doesn't, terminates it forcibly.  */
  83
  84 #include <stddef.h>
  85 #include <errno.h>
  86
  87 /* must include CRT headers *before* config.h */
  88 #include <config.h>
  89
  90 #include <windows.h>
  91
  92 #include "lisp.h"
  93 #include "w32term.h"    /* for enter_crit/leave_crit and WM_EMACS_FILENOTIFY */
  94 #include "w32common.h"  /* for OS version data */
  95 #include "w32.h"        /* for w32_strerror */
  96 #include "coding.h"
  97 #include "keyboard.h"
  98 #include "frame.h"      /* needed by termhooks.h */
  99 #include "termhooks.h"  /* for FILE_NOTIFY_EVENT */
 100
 101 #define DIRWATCH_SIGNATURE 0x01233210
 102
 103 struct notification {
 104   BYTE *buf;            /* buffer for ReadDirectoryChangesW */
 105   OVERLAPPED *io_info;  /* the OVERLAPPED structure for async I/O */
 106   BOOL subtree;         /* whether to watch subdirectories */
 107   DWORD filter;         /* bit mask for events to watch */
 108   char *watchee;        /* the file we are interested in, UTF-8 encoded */
 109   HANDLE dir;           /* handle to the watched directory */
 110   HANDLE thr;           /* handle to the thread that watches */
 111   volatile int terminate; /* if non-zero, request for the thread to terminate */
 112   unsigned signature;
 113 };
 114
 115 /* Used for communicating notifications to the main thread.  */
 116 volatile int notification_buffer_in_use;
 117 BYTE file_notifications[16384];
 118 DWORD notifications_size;
 119 void *notifications_desc;
 120
 121 static Lisp_Object Qfile_name, Qdirectory_name, Qattributes, Qsize;
 122 static Lisp_Object Qlast_write_time, Qlast_access_time, Qcreation_time;
 123 static Lisp_Object Qsecurity_desc, Qsubtree, watch_list;
 124
 125 /* Signal to the main thread that we have file notifications for it to
 126    process.  */
 127 static void
 128 send_notifications (BYTE *info, DWORD info_size, void *desc,
 129                     volatile int *terminate)
 130 {
 131   int done = 0;
 132   struct frame *f = SELECTED_FRAME ();
 133
 134   /* A single buffer is used to communicate all notifications to the
 135      main thread.  Since both the main thread and several watcher
 136      threads could be active at the same time, we use a critical area
 137      and an "in-use" flag to synchronize them.  A watcher thread can
 138      only put its notifications in the buffer if it acquires the
 139      critical area and finds the "in-use" flag reset.  The main thread
 140      resets the flag after it is done processing notifications.
 141
 142      FIXME: is there a better way of dealing with this?  */
 143   while (!done && !*terminate)
 144     {
 145       enter_crit ();
 146       if (!notification_buffer_in_use)
 147         {
 148           if (info_size)
 149             memcpy (file_notifications, info, info_size);
 150           notifications_size = info_size;
 151           notifications_desc = desc;
 152           /* If PostMessage fails, the message queue is full.  If that
 153              happens, the last thing they will worry about is file
 154              notifications.  So we effectively discard the
 155              notification in that case.  */
 156           if ((FRAME_TERMCAP_P (f)
 157                /* We send the message to the main (a.k.a. "Lisp")
 158                   thread, where it will wake up MsgWaitForMultipleObjects
 159                   inside sys_select, causing it to report that there's
 160                   some keyboard input available.  This will in turn cause
 161                   w32_console_read_socket to be called, which will pick
 162                   up the file notifications.  */
 163                && PostThreadMessage (dwMainThreadId, WM_EMACS_FILENOTIFY, 0, 0))
 164               || (FRAME_W32_P (f)
 165                   && PostMessage (FRAME_W32_WINDOW (f),
 166                                   WM_EMACS_FILENOTIFY, 0, 0))
 167               /* When we are running in batch mode, there's no one to
 168                  send a message, so we just signal the data is
 169                  available and hope sys_select will be called soon and
 170                  will read the data.  */
 171               || (FRAME_INITIAL_P (f) && noninteractive))
 172             notification_buffer_in_use = 1;
 173           done = 1;
 174         }
 175       leave_crit ();
 176       if (!done)
 177         Sleep (5);
 178     }
 179 }
 180
 181 /* An APC routine to cancel outstanding directory watch.  Invoked by
 182    the main thread via QueueUserAPC.  This is needed because only the
 183    thread that issued the ReadDirectoryChangesW call can call CancelIo
 184    to cancel that.  (CancelIoEx is only available since Vista, so we
 185    cannot use it on XP.)  */
 186 VOID CALLBACK
 187 watch_end (ULONG_PTR arg)
 188 {
 189   HANDLE hdir = (HANDLE)arg;
 190
 191   if (hdir && hdir != INVALID_HANDLE_VALUE)
 192     {
 193       CancelIo (hdir);
 194       CloseHandle (hdir);
 195     }
 196 }
 197
 198 /* A completion routine (a.k.a. "APC function") for handling events
 199    read by ReadDirectoryChangesW.  Called by the OS when the thread
 200    which issued the asynchronous ReadDirectoryChangesW call is in the
 201    "alertable state", i.e. waiting inside SleepEx call.  */
 202 VOID CALLBACK
 203 watch_completion (DWORD status, DWORD bytes_ret, OVERLAPPED *io_info)
 204 {
 205   struct notification *dirwatch;
 206
 207   /* Who knows what happened?  Perhaps the OVERLAPPED structure was
 208      freed by someone already?  In any case, we cannot do anything
 209      with this request, so just punt and skip it.  FIXME: should we
 210      raise the 'terminate' flag in this case?  */
 211   if (!io_info)
 212     return;
 213
 214   /* We have a pointer to our dirwatch structure conveniently stashed
 215      away in the hEvent member of the OVERLAPPED struct.  According to
 216      MSDN documentation of ReadDirectoryChangesW: "The hEvent member
 217      of the OVERLAPPED structure is not used by the system, so you can
 218      use it yourself."  */
 219   dirwatch = (struct notification *)io_info->hEvent;
 220   if (status == ERROR_OPERATION_ABORTED)
 221     {
 222       /* We've been called because the main thread told us to issue
 223          CancelIo on the directory we watch, and watch_end did so.
 224          The directory handle is already closed.  We should clean up
 225          and exit, signaling to the thread worker routine not to
 226          issue another call to ReadDirectoryChangesW.  Note that we
 227          don't free the dirwatch object itself nor the memory consumed
 228          by its buffers; this is done by the main thread in
 229          remove_watch.  Calling malloc/free from a thread other than
 230          the main thread is a no-no.  */
 231       dirwatch->dir = NULL;
 232       dirwatch->terminate = 1;
 233     }
 234   else
 235     {
 236       /* Tell the main thread we have notifications for it.  */
 237       send_notifications (dirwatch->buf, bytes_ret, dirwatch,
 238                           &dirwatch->terminate);
 239     }
 240 }
 241
 242 /* Worker routine for the watch thread.  */
 243 static DWORD WINAPI
 244 watch_worker (LPVOID arg)
 245 {
 246   struct notification *dirwatch = (struct notification *)arg;
 247
 248   do {
 249     BOOL status;
 250     DWORD bytes_ret = 0;
 251
 252     if (dirwatch->dir)
 253       {
 254         status = ReadDirectoryChangesW (dirwatch->dir, dirwatch->buf, 16384,
 255                                         dirwatch->subtree, dirwatch->filter,
 256                                         &bytes_ret,
 257                                         dirwatch->io_info, watch_completion);
 258         if (!status)
 259           {
 260             DebPrint (("watch_worker, abnormal exit: %lu\n", GetLastError ()));
 261             /* We cannot remove the dirwatch object from watch_list,
 262                because we are in a separate thread.  For the same
 263                reason, we also cannot free memory consumed by the
 264                buffers allocated for the dirwatch object.  So we close
 265                the directory handle, but do not free the object itself
 266                or its buffers.  We also don't touch the signature.
 267                This way, remove_watch can still identify the object,
 268                remove it, and free its memory.  */
 269             CloseHandle (dirwatch->dir);
 270             dirwatch->dir = NULL;
 271             return 1;
 272           }
 273       }
 274     /* Sleep indefinitely until awoken by the I/O completion, which
 275        could be either a change notification or a cancellation of the
 276        watch.  */
 277     SleepEx (INFINITE, TRUE);
 278   } while (!dirwatch->terminate);
 279
 280   return 0;
 281 }
 282
 283 /* Launch a thread to watch changes to FILE in a directory open on
 284    handle HDIR.  */
 285 static struct notification *
 286 start_watching (const char *file, HANDLE hdir, BOOL subdirs, DWORD flags)
 287 {
 288   struct notification *dirwatch = xzalloc (sizeof (struct notification));
 289
 290   dirwatch->signature = DIRWATCH_SIGNATURE;
 291   dirwatch->buf = xmalloc (16384);
 292   dirwatch->io_info = xzalloc (sizeof(OVERLAPPED));
 293   /* Stash a pointer to dirwatch structure for use by the completion
 294      routine.  According to MSDN documentation of ReadDirectoryChangesW:
 295      "The hEvent member of the OVERLAPPED structure is not used by the
 296      system, so you can use it yourself." */
 297   dirwatch->io_info->hEvent = dirwatch;
 298   dirwatch->subtree = subdirs;
 299   dirwatch->filter = flags;
 300   dirwatch->watchee = xstrdup (file);
 301   dirwatch->terminate = 0;
 302   dirwatch->dir = hdir;
 303
 304   /* See w32proc.c where it calls CreateThread for the story behind
 305      the 2nd and 5th argument in the call to CreateThread.  */
 306   dirwatch->thr = CreateThread (NULL, 64 * 1024, watch_worker, (void *)dirwatch,
 307                                 0x00010000, NULL);
 308
 309   if (!dirwatch->thr)
 310     {
 311       xfree (dirwatch->buf);
 312       xfree (dirwatch->io_info);
 313       xfree (dirwatch->watchee);
 314       xfree (dirwatch);
 315       dirwatch = NULL;
 316     }
 317   return dirwatch;
 318 }
 319
 320 /* Called from the main thread to start watching FILE in PARENT_DIR,
 321    subject to FLAGS.  If SUBDIRS is TRUE, watch the subdirectories of
 322    PARENT_DIR as well.  Value is a pointer to 'struct notification'
 323    used by the thread that watches the changes.  */
 324 static struct notification *
 325 add_watch (const char *parent_dir, const char *file, BOOL subdirs, DWORD flags)
 326 {
 327   HANDLE hdir;
 328   struct notification *dirwatch = NULL;
 329
 330   if (!file)
 331     return NULL;
 332
 333   if (w32_unicode_filenames)
 334     {
 335       wchar_t dir_w[MAX_PATH], file_w[MAX_PATH];
 336
 337       filename_to_utf16 (parent_dir, dir_w);
 338       if (*file)
 339         filename_to_utf16 (file, file_w);
 340       else
 341         file_w[0] = 0;
 342
 343       hdir = CreateFileW (dir_w,
 344                           FILE_LIST_DIRECTORY,
 345                           /* FILE_SHARE_DELETE doesn't preclude other
 346                              processes from deleting files inside
 347                              parent_dir.  */
 348                           FILE_SHARE_READ|FILE_SHARE_WRITE|FILE_SHARE_DELETE,
 349                           NULL, OPEN_EXISTING,
 350                           FILE_FLAG_BACKUP_SEMANTICS | FILE_FLAG_OVERLAPPED,
 351                           NULL);
 352     }
 353   else
 354     {
 355       char dir_a[MAX_PATH], file_a[MAX_PATH];
 356
 357       filename_to_ansi (parent_dir, dir_a);
 358       if (*file)
 359         filename_to_ansi (file, file_a);
 360       else
 361         file_a[0] = '\0';
 362
 363       hdir = CreateFileA (dir_a,
 364                           FILE_LIST_DIRECTORY,
 365                           FILE_SHARE_READ|FILE_SHARE_WRITE|FILE_SHARE_DELETE,
 366                           NULL, OPEN_EXISTING,
 367                           FILE_FLAG_BACKUP_SEMANTICS | FILE_FLAG_OVERLAPPED,
 368                           NULL);
 369     }
 370   if (hdir == INVALID_HANDLE_VALUE)
 371     return NULL;
 372
 373   if ((dirwatch = start_watching (file, hdir, subdirs, flags)) == NULL)
 374     CloseHandle (hdir);
 375
 376   return dirwatch;
 377 }
 378
 379 /* Stop watching a directory specified by a pointer to its dirwatch object.  */
 380 static int
 381 remove_watch (struct notification *dirwatch)
 382 {
 383   if (dirwatch && dirwatch->signature == DIRWATCH_SIGNATURE)
 384     {
 385       int i;
 386       BOOL status;
 387       DWORD exit_code, err;
 388
 389       /* Only the thread that issued the outstanding I/O call can call
 390          CancelIo on it.  (CancelIoEx is available only since Vista.)
 391          So we need to queue an APC for the worker thread telling it
 392          to terminate.  */
 393       if (!QueueUserAPC (watch_end, dirwatch->thr, (ULONG_PTR)dirwatch->dir))
 394         DebPrint (("QueueUserAPC failed (%lu)!\n", GetLastError ()));
 395       /* We also set the terminate flag, for when the thread is
 396          waiting on the critical section that never gets acquired.
 397          FIXME: is there a cleaner method?  Using SleepEx there is a
 398          no-no, as that will lead to recursive APC invocations and
 399          stack overflow.  */
 400       dirwatch->terminate = 1;
 401       /* Wait for the thread to exit.  FIXME: is there a better method
 402          that is not overly complex?  */
 403       for (i = 0; i < 50; i++)
 404         {
 405           if (!((status = GetExitCodeThread (dirwatch->thr, &exit_code))
 406                 && exit_code == STILL_ACTIVE))
 407             break;
 408           Sleep (10);
 409         }
 410       if ((status == FALSE && (err = GetLastError ()) == ERROR_INVALID_HANDLE)
 411           || exit_code == STILL_ACTIVE)
 412         {
 413           if (!(status == FALSE && err == ERROR_INVALID_HANDLE))
 414             {
 415               TerminateThread (dirwatch->thr, 0);
 416               if (dirwatch->dir)
 417                 CloseHandle (dirwatch->dir);
 418             }
 419         }
 420
 421       /* Clean up.  */
 422       if (dirwatch->thr)
 423         {
 424           CloseHandle (dirwatch->thr);
 425           dirwatch->thr = NULL;
 426         }
 427       xfree (dirwatch->buf);
 428       xfree (dirwatch->io_info);
 429       xfree (dirwatch->watchee);
 430       xfree (dirwatch);
 431
 432       return 0;
 433     }
 434   else
 435     {
 436       DebPrint (("Unknown dirwatch object!\n"));
 437       return -1;
 438     }
 439 }
 440
 441 static DWORD
 442 filter_list_to_flags (Lisp_Object filter_list)
 443 {
 444   DWORD flags = 0;
 445
 446   if (NILP (filter_list))
 447     return flags;
 448
 449   if (!NILP (Fmember (Qfile_name, filter_list)))
 450     flags |= FILE_NOTIFY_CHANGE_FILE_NAME;
 451   if (!NILP (Fmember (Qdirectory_name, filter_list)))
 452     flags |= FILE_NOTIFY_CHANGE_DIR_NAME;
 453   if (!NILP (Fmember (Qattributes, filter_list)))
 454     flags |= FILE_NOTIFY_CHANGE_ATTRIBUTES;
 455   if (!NILP (Fmember (Qsize, filter_list)))
 456     flags |= FILE_NOTIFY_CHANGE_SIZE;
 457   if (!NILP (Fmember (Qlast_write_time, filter_list)))
 458     flags |= FILE_NOTIFY_CHANGE_LAST_WRITE;
 459   if (!NILP (Fmember (Qlast_access_time, filter_list)))
 460     flags |= FILE_NOTIFY_CHANGE_LAST_ACCESS;
 461   if (!NILP (Fmember (Qcreation_time, filter_list)))
 462     flags |= FILE_NOTIFY_CHANGE_CREATION;
 463   if (!NILP (Fmember (Qsecurity_desc, filter_list)))
 464     flags |= FILE_NOTIFY_CHANGE_SECURITY;
 465
 466   return flags;
 467 }
 468
 469 DEFUN ("w32notify-add-watch", Fw32notify_add_watch,
 470        Sw32notify_add_watch, 3, 3, 0,
 471        doc: /* Add a watch for filesystem events pertaining to FILE.
 472
 473 This arranges for filesystem events pertaining to FILE to be reported
 474 to Emacs.  Use `w32notify-rm-watch' to cancel the watch.
 475
 476 Value is a descriptor for the added watch.  If the file cannot be
 477 watched for some reason, this function signals a `file-error' error.
 478
 479 FILTER is a list of conditions for reporting an event.  It can include
 480 the following symbols:
 481
 482   'file-name'          -- report file creation, deletion, or renaming
 483   'directory-name'     -- report directory creation, deletion, or renaming
 484   'attributes'         -- report changes in attributes
 485   'size'               -- report changes in file-size
 486   'last-write-time'    -- report changes in last-write time
 487   'last-access-time'   -- report changes in last-access time
 488   'creation-time'      -- report changes in creation time
 489   'security-desc'      -- report changes in security descriptor
 490
 491 If FILE is a directory, and FILTER includes 'subtree', then all the
 492 subdirectories will also be watched and changes in them reported.
 493
 494 When any event happens that satisfies the conditions specified by
 495 FILTER, Emacs will call the CALLBACK function passing it a single
 496 argument EVENT, which is of the form
 497
 498   (DESCRIPTOR ACTION FILE)
 499
 500 DESCRIPTOR is the same object as the one returned by this function.
 501 ACTION is the description of the event.  It could be any one of the
 502 following:
 503
 504   'added'        -- FILE was added
 505   'removed'      -- FILE was deleted
 506   'modified'     -- FILE's contents or its attributes were modified
 507   'renamed-from' -- a file was renamed whose old name was FILE
 508   'renamed-to'   -- a file was renamed and its new name is FILE
 509
 510 FILE is the name of the file whose event is being reported.
 511
 512 Note that some networked filesystems, such as Samba-mounted Unix
 513 volumes, might not send notifications about file changes.  In these
 514 cases, this function will return a valid descriptor, but notifications
 515 will never come in.  Volumes shared from remote Windows machines do
 516 generate notifications correctly, though.  */)
 517   (Lisp_Object file, Lisp_Object filter, Lisp_Object callback)
 518 {
 519   Lisp_Object dirfn, basefn, watch_object, watch_descriptor;
 520   DWORD flags;
 521   BOOL subdirs = FALSE;
 522   struct notification *dirwatch = NULL;
 523   Lisp_Object lisp_errstr;
 524   char *errstr;
 525
 526   CHECK_LIST (filter);
 527
 528   /* The underlying features are available only since XP.  */
 529   if (os_subtype == OS_9X
 530       || (w32_major_version == 5 && w32_major_version < 1))
 531     {
 532       errno = ENOSYS;
 533       report_file_error ("Watching filesystem events is not supported",
 534                          Qnil);
 535     }
 536
 537   /* filenotify.el always passes us a directory, either the parent
 538      directory of a file to be watched, or the directory to be
 539      watched.  */
 540   file = Fdirectory_file_name (Fexpand_file_name (file, Qnil));
 541   if (NILP (Ffile_directory_p (file)))
 542     {
 543       /* This should only happen if we are called directly, not via
 544          filenotify.el.  If BASEFN is empty, the argument was the root
 545          directory on its drive.  */
 546       dirfn = ENCODE_FILE (Ffile_name_directory (file));
 547       basefn = ENCODE_FILE (Ffile_name_nondirectory (file));
 548       if (*SDATA (basefn) == '\0')
 549         subdirs = TRUE;
 550     }
 551   else
 552     {
 553       dirfn = ENCODE_FILE (file);
 554       basefn = Qnil;
 555     }
 556
 557   if (!NILP (Fmember (Qsubtree, filter)))
 558     subdirs = TRUE;
 559
 560   flags = filter_list_to_flags (filter);
 561
 562   dirwatch = add_watch (SSDATA (dirfn), NILP (basefn) ? "" : SSDATA (basefn),
 563                         subdirs, flags);
 564   if (!dirwatch)
 565     {
 566       DWORD err = GetLastError ();
 567
 568       errno = EINVAL;
 569       if (err)
 570         {
 571           errstr = w32_strerror (err);
 572           if (!NILP (Vlocale_coding_system))
 573             lisp_errstr
 574               = code_convert_string_norecord (build_unibyte_string (errstr),
 575                                               Vlocale_coding_system, 0);
 576           else
 577             lisp_errstr = build_string (errstr);
 578           report_file_error ("Cannot watch file",
 579                              Fcons (lisp_errstr, Fcons (file, Qnil)));
 580         }
 581       else
 582         report_file_error ("Cannot watch file", Fcons (file, Qnil));
 583     }
 584   /* Store watch object in watch list. */
 585   watch_descriptor = XIL ((EMACS_INT)dirwatch);
 586   watch_object = Fcons (watch_descriptor, callback);
 587   watch_list = Fcons (watch_object, watch_list);
 588
 589   return watch_descriptor;
 590 }
 591
 592 DEFUN ("w32notify-rm-watch", Fw32notify_rm_watch,
 593        Sw32notify_rm_watch, 1, 1, 0,
 594        doc: /* Remove an existing watch specified by its WATCH-DESCRIPTOR.
 595
 596 WATCH-DESCRIPTOR should be an object returned by `w32notify-add-watch'.  */)
 597      (Lisp_Object watch_descriptor)
 598 {
 599   Lisp_Object watch_object;
 600   struct notification *dirwatch;
 601   int status = -1;
 602
 603   /* Remove the watch object from watch list.  Do this before freeing
 604      the object, do that even if we fail to free it, watch_list is
 605      kept free of junk.  */
 606   watch_object = Fassoc (watch_descriptor, watch_list);
 607   if (!NILP (watch_object))
 608     {
 609       watch_list = Fdelete (watch_object, watch_list);
 610       dirwatch = (struct notification *)XLI (watch_descriptor);
 611       if (w32_valid_pointer_p (dirwatch, sizeof(struct notification)))
 612         status = remove_watch (dirwatch);
 613     }
 614
 615   if (status == -1)
 616     report_file_error ("Invalid watch descriptor", Fcons (watch_descriptor,
 617                                                           Qnil));
 618
 619   return Qnil;
 620 }
 621
 622 Lisp_Object
 623 w32_get_watch_object (void *desc)
 624 {
 625   Lisp_Object descriptor = XIL ((EMACS_INT)desc);
 626
 627   /* This is called from the input queue handling code, inside a
 628      critical section, so we cannot possibly QUIT if watch_list is not
 629      in the right condition.  */
 630   return NILP (watch_list) ? Qnil : assoc_no_quit (descriptor, watch_list);
 631 }
 632
 633 void
 634 globals_of_w32notify (void)
 635 {
 636   watch_list = Qnil;
 637 }
 638
 639 void
 640 syms_of_w32notify (void)
 641 {
 642   DEFSYM (Qfile_name, "file-name");
 643   DEFSYM (Qdirectory_name, "directory-name");
 644   DEFSYM (Qattributes, "attributes");
 645   DEFSYM (Qsize, "size");
 646   DEFSYM (Qlast_write_time, "last-write-time");
 647   DEFSYM (Qlast_access_time, "last-access-time");
 648   DEFSYM (Qcreation_time, "creation-time");
 649   DEFSYM (Qsecurity_desc, "security-desc");
 650   DEFSYM (Qsubtree, "subtree");
 651
 652   defsubr (&Sw32notify_add_watch);
 653   defsubr (&Sw32notify_rm_watch);
 654
 655   staticpro (&watch_list);
 656
 657   Fprovide (intern_c_string ("w32notify"), Qnil);
 658 }