src/w32notify.c

   1 /* Filesystem notifications support for GNU Emacs on the Microsoft Windows API.
   2    Copyright (C) 2012-2015 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 watch_list;
 122
 123 /* Signal to the main thread that we have file notifications for it to
 124    process.  */
 125 static void
 126 send_notifications (BYTE *info, DWORD info_size, void *desc,
 127                     volatile int *terminate)
 128 {
 129   int done = 0;
 130   struct frame *f = SELECTED_FRAME ();
 131
 132   /* A single buffer is used to communicate all notifications to the
 133      main thread.  Since both the main thread and several watcher
 134      threads could be active at the same time, we use a critical area
 135      and an "in-use" flag to synchronize them.  A watcher thread can
 136      only put its notifications in the buffer if it acquires the
 137      critical area and finds the "in-use" flag reset.  The main thread
 138      resets the flag after it is done processing notifications.
 139
 140      FIXME: is there a better way of dealing with this?  */
 141   while (!done && !*terminate)
 142     {
 143       enter_crit ();
 144       if (!notification_buffer_in_use)
 145         {
 146           if (info_size)
 147             memcpy (file_notifications, info, info_size);
 148           notifications_size = info_size;
 149           notifications_desc = desc;
 150           /* If PostMessage fails, the message queue is full.  If that
 151              happens, the last thing they will worry about is file
 152              notifications.  So we effectively discard the
 153              notification in that case.  */
 154           if ((FRAME_TERMCAP_P (f)
 155                /* We send the message to the main (a.k.a. "Lisp")
 156                   thread, where it will wake up MsgWaitForMultipleObjects
 157                   inside sys_select, causing it to report that there's
 158                   some keyboard input available.  This will in turn cause
 159                   w32_console_read_socket to be called, which will pick
 160                   up the file notifications.  */
 161                && PostThreadMessage (dwMainThreadId, WM_EMACS_FILENOTIFY, 0, 0))
 162               || (FRAME_W32_P (f)
 163                   && PostMessage (FRAME_W32_WINDOW (f),
 164                                   WM_EMACS_FILENOTIFY, 0, 0))
 165               /* When we are running in batch mode, there's no one to
 166                  send a message, so we just signal the data is
 167                  available and hope sys_select will be called soon and
 168                  will read the data.  */
 169               || (FRAME_INITIAL_P (f) && noninteractive))
 170             notification_buffer_in_use = 1;
 171           done = 1;
 172         }
 173       leave_crit ();
 174       if (!done)
 175         Sleep (5);
 176     }
 177 }
 178
 179 /* An APC routine to cancel outstanding directory watch.  Invoked by
 180    the main thread via QueueUserAPC.  This is needed because only the
 181    thread that issued the ReadDirectoryChangesW call can call CancelIo
 182    to cancel that.  (CancelIoEx is only available since Vista, so we
 183    cannot use it on XP.)  */
 184 VOID CALLBACK
 185 watch_end (ULONG_PTR arg)
 186 {
 187   HANDLE hdir = (HANDLE)arg;
 188
 189   if (hdir && hdir != INVALID_HANDLE_VALUE)
 190     {
 191       CancelIo (hdir);
 192       CloseHandle (hdir);
 193     }
 194 }
 195
 196 /* A completion routine (a.k.a. "APC function") for handling events
 197    read by ReadDirectoryChangesW.  Called by the OS when the thread
 198    which issued the asynchronous ReadDirectoryChangesW call is in the
 199    "alertable state", i.e. waiting inside SleepEx call.  */
 200 VOID CALLBACK
 201 watch_completion (DWORD status, DWORD bytes_ret, OVERLAPPED *io_info)
 202 {
 203   struct notification *dirwatch;
 204
 205   /* Who knows what happened?  Perhaps the OVERLAPPED structure was
 206      freed by someone already?  In any case, we cannot do anything
 207      with this request, so just punt and skip it.  FIXME: should we
 208      raise the 'terminate' flag in this case?  */
 209   if (!io_info)
 210     return;
 211
 212   /* We have a pointer to our dirwatch structure conveniently stashed
 213      away in the hEvent member of the OVERLAPPED struct.  According to
 214      MSDN documentation of ReadDirectoryChangesW: "The hEvent member
 215      of the OVERLAPPED structure is not used by the system, so you can
 216      use it yourself."  */
 217   dirwatch = (struct notification *)io_info->hEvent;
 218   if (status == ERROR_OPERATION_ABORTED)
 219     {
 220       /* We've been called because the main thread told us to issue
 221          CancelIo on the directory we watch, and watch_end did so.
 222          The directory handle is already closed.  We should clean up
 223          and exit, signaling to the thread worker routine not to
 224          issue another call to ReadDirectoryChangesW.  Note that we
 225          don't free the dirwatch object itself nor the memory consumed
 226          by its buffers; this is done by the main thread in
 227          remove_watch.  Calling malloc/free from a thread other than
 228          the main thread is a no-no.  */
 229       dirwatch->dir = NULL;
 230       dirwatch->terminate = 1;
 231     }
 232   else
 233     {
 234       /* Tell the main thread we have notifications for it.  */
 235       send_notifications (dirwatch->buf, bytes_ret, dirwatch,
 236                           &dirwatch->terminate);
 237     }
 238 }
 239
 240 /* Worker routine for the watch thread.  */
 241 static DWORD WINAPI
 242 watch_worker (LPVOID arg)
 243 {
 244   struct notification *dirwatch = (struct notification *)arg;
 245
 246   do {
 247     BOOL status;
 248     DWORD bytes_ret = 0;
 249
 250     if (dirwatch->dir)
 251       {
 252         status = ReadDirectoryChangesW (dirwatch->dir, dirwatch->buf, 16384,
 253                                         dirwatch->subtree, dirwatch->filter,
 254                                         &bytes_ret,
 255                                         dirwatch->io_info, watch_completion);
 256         if (!status)
 257           {
 258             DebPrint (("watch_worker, abnormal exit: %lu\n", GetLastError ()));
 259             /* We cannot remove the dirwatch object from watch_list,
 260                because we are in a separate thread.  For the same
 261                reason, we also cannot free memory consumed by the
 262                buffers allocated for the dirwatch object.  So we close
 263                the directory handle, but do not free the object itself
 264                or its buffers.  We also don't touch the signature.
 265                This way, remove_watch can still identify the object,
 266                remove it, and free its memory.  */
 267             CloseHandle (dirwatch->dir);
 268             dirwatch->dir = NULL;
 269             return 1;
 270           }
 271       }
 272     /* Sleep indefinitely until awoken by the I/O completion, which
 273        could be either a change notification or a cancellation of the
 274        watch.  */
 275     SleepEx (INFINITE, TRUE);
 276   } while (!dirwatch->terminate);
 277
 278   return 0;
 279 }
 280
 281 /* Launch a thread to watch changes to FILE in a directory open on
 282    handle HDIR.  */
 283 static struct notification *
 284 start_watching (const char *file, HANDLE hdir, BOOL subdirs, DWORD flags)
 285 {
 286   struct notification *dirwatch = xzalloc (sizeof (struct notification));
 287
 288   dirwatch->signature = DIRWATCH_SIGNATURE;
 289   dirwatch->buf = xmalloc (16384);
 290   dirwatch->io_info = xzalloc (sizeof(OVERLAPPED));
 291   /* Stash a pointer to dirwatch structure for use by the completion
 292      routine.  According to MSDN documentation of ReadDirectoryChangesW:
 293      "The hEvent member of the OVERLAPPED structure is not used by the
 294      system, so you can use it yourself." */
 295   dirwatch->io_info->hEvent = dirwatch;
 296   dirwatch->subtree = subdirs;
 297   dirwatch->filter = flags;
 298   dirwatch->watchee = xstrdup (file);
 299   dirwatch->terminate = 0;
 300   dirwatch->dir = hdir;
 301
 302   /* See w32proc.c where it calls CreateThread for the story behind
 303      the 2nd and 5th argument in the call to CreateThread.  */
 304   dirwatch->thr = CreateThread (NULL, 64 * 1024, watch_worker, (void *)dirwatch,
 305                                 0x00010000, NULL);
 306
 307   if (!dirwatch->thr)
 308     {
 309       xfree (dirwatch->buf);
 310       xfree (dirwatch->io_info);
 311       xfree (dirwatch->watchee);
 312       xfree (dirwatch);
 313       dirwatch = NULL;
 314     }
 315   return dirwatch;
 316 }
 317
 318 /* Called from the main thread to start watching FILE in PARENT_DIR,
 319    subject to FLAGS.  If SUBDIRS is TRUE, watch the subdirectories of
 320    PARENT_DIR as well.  Value is a pointer to 'struct notification'
 321    used by the thread that watches the changes.  */
 322 static struct notification *
 323 add_watch (const char *parent_dir, const char *file, BOOL subdirs, DWORD flags)
 324 {
 325   HANDLE hdir;
 326   struct notification *dirwatch = NULL;
 327
 328   if (!file)
 329     return NULL;
 330
 331   if (w32_unicode_filenames)
 332     {
 333       wchar_t dir_w[MAX_PATH], file_w[MAX_PATH];
 334
 335       filename_to_utf16 (parent_dir, dir_w);
 336       if (*file)
 337         filename_to_utf16 (file, file_w);
 338       else
 339         file_w[0] = 0;
 340
 341       hdir = CreateFileW (dir_w,
 342                           FILE_LIST_DIRECTORY,
 343                           /* FILE_SHARE_DELETE doesn't preclude other
 344                              processes from deleting files inside
 345                              parent_dir.  */
 346                           FILE_SHARE_READ|FILE_SHARE_WRITE|FILE_SHARE_DELETE,
 347                           NULL, OPEN_EXISTING,
 348                           FILE_FLAG_BACKUP_SEMANTICS | FILE_FLAG_OVERLAPPED,
 349                           NULL);
 350     }
 351   else
 352     {
 353       char dir_a[MAX_PATH], file_a[MAX_PATH];
 354
 355       filename_to_ansi (parent_dir, dir_a);
 356       if (*file)
 357         filename_to_ansi (file, file_a);
 358       else
 359         file_a[0] = '\0';
 360
 361       hdir = CreateFileA (dir_a,
 362                           FILE_LIST_DIRECTORY,
 363                           FILE_SHARE_READ|FILE_SHARE_WRITE|FILE_SHARE_DELETE,
 364                           NULL, OPEN_EXISTING,
 365                           FILE_FLAG_BACKUP_SEMANTICS | FILE_FLAG_OVERLAPPED,
 366                           NULL);
 367     }
 368   if (hdir == INVALID_HANDLE_VALUE)
 369     return NULL;
 370
 371   if ((dirwatch = start_watching (file, hdir, subdirs, flags)) == NULL)
 372     CloseHandle (hdir);
 373
 374   return dirwatch;
 375 }
 376
 377 /* Stop watching a directory specified by a pointer to its dirwatch object.  */
 378 static int
 379 remove_watch (struct notification *dirwatch)
 380 {
 381   if (dirwatch && dirwatch->signature == DIRWATCH_SIGNATURE)
 382     {
 383       int i;
 384       BOOL status;
 385       DWORD exit_code, err;
 386
 387       /* Only the thread that issued the outstanding I/O call can call
 388          CancelIo on it.  (CancelIoEx is available only since Vista.)
 389          So we need to queue an APC for the worker thread telling it
 390          to terminate.  */
 391       if (!QueueUserAPC (watch_end, dirwatch->thr, (ULONG_PTR)dirwatch->dir))
 392         DebPrint (("QueueUserAPC failed (%lu)!\n", GetLastError ()));
 393       /* We also set the terminate flag, for when the thread is
 394          waiting on the critical section that never gets acquired.
 395          FIXME: is there a cleaner method?  Using SleepEx there is a
 396          no-no, as that will lead to recursive APC invocations and
 397          stack overflow.  */
 398       dirwatch->terminate = 1;
 399       /* Wait for the thread to exit.  FIXME: is there a better method
 400          that is not overly complex?  */
 401       for (i = 0; i < 50; i++)
 402         {
 403           if (!((status = GetExitCodeThread (dirwatch->thr, &exit_code))
 404                 && exit_code == STILL_ACTIVE))
 405             break;
 406           Sleep (10);
 407         }
 408       if ((status == FALSE && (err = GetLastError ()) == ERROR_INVALID_HANDLE)
 409           || exit_code == STILL_ACTIVE)
 410         {
 411           if (!(status == FALSE && err == ERROR_INVALID_HANDLE))
 412             {
 413               TerminateThread (dirwatch->thr, 0);
 414               if (dirwatch->dir)
 415                 CloseHandle (dirwatch->dir);
 416             }
 417         }
 418
 419       /* Clean up.  */
 420       if (dirwatch->thr)
 421         {
 422           CloseHandle (dirwatch->thr);
 423           dirwatch->thr = NULL;
 424         }
 425       xfree (dirwatch->buf);
 426       xfree (dirwatch->io_info);
 427       xfree (dirwatch->watchee);
 428       xfree (dirwatch);
 429
 430       return 0;
 431     }
 432   else
 433     {
 434       DebPrint (("Unknown dirwatch object!\n"));
 435       return -1;
 436     }
 437 }
 438
 439 static DWORD
 440 filter_list_to_flags (Lisp_Object filter_list)
 441 {
 442   DWORD flags = 0;
 443
 444   if (NILP (filter_list))
 445     return flags;
 446
 447   if (!NILP (Fmember (Qfile_name, filter_list)))
 448     flags |= FILE_NOTIFY_CHANGE_FILE_NAME;
 449   if (!NILP (Fmember (Qdirectory_name, filter_list)))
 450     flags |= FILE_NOTIFY_CHANGE_DIR_NAME;
 451   if (!NILP (Fmember (Qattributes, filter_list)))
 452     flags |= FILE_NOTIFY_CHANGE_ATTRIBUTES;
 453   if (!NILP (Fmember (Qsize, filter_list)))
 454     flags |= FILE_NOTIFY_CHANGE_SIZE;
 455   if (!NILP (Fmember (Qlast_write_time, filter_list)))
 456     flags |= FILE_NOTIFY_CHANGE_LAST_WRITE;
 457   if (!NILP (Fmember (Qlast_access_time, filter_list)))
 458     flags |= FILE_NOTIFY_CHANGE_LAST_ACCESS;
 459   if (!NILP (Fmember (Qcreation_time, filter_list)))
 460     flags |= FILE_NOTIFY_CHANGE_CREATION;
 461   if (!NILP (Fmember (Qsecurity_desc, filter_list)))
 462     flags |= FILE_NOTIFY_CHANGE_SECURITY;
 463
 464   return flags;
 465 }
 466
 467 DEFUN ("w32notify-add-watch", Fw32notify_add_watch,
 468        Sw32notify_add_watch, 3, 3, 0,
 469        doc: /* Add a watch for filesystem events pertaining to FILE.
 470
 471 This arranges for filesystem events pertaining to FILE to be reported
 472 to Emacs.  Use `w32notify-rm-watch' to cancel the watch.
 473
 474 Value is a descriptor for the added watch.  If the file cannot be
 475 watched for some reason, this function signals a `file-error' error.
 476
 477 FILTER is a list of conditions for reporting an event.  It can include
 478 the following symbols:
 479
 480   'file-name'          -- report file creation, deletion, or renaming
 481   'directory-name'     -- report directory creation, deletion, or renaming
 482   'attributes'         -- report changes in attributes
 483   'size'               -- report changes in file-size
 484   'last-write-time'    -- report changes in last-write time
 485   'last-access-time'   -- report changes in last-access time
 486   'creation-time'      -- report changes in creation time
 487   'security-desc'      -- report changes in security descriptor
 488
 489 If FILE is a directory, and FILTER includes 'subtree', then all the
 490 subdirectories will also be watched and changes in them reported.
 491
 492 When any event happens that satisfies the conditions specified by
 493 FILTER, Emacs will call the CALLBACK function passing it a single
 494 argument EVENT, which is of the form
 495
 496   (DESCRIPTOR ACTION FILE)
 497
 498 DESCRIPTOR is the same object as the one returned by this function.
 499 ACTION is the description of the event.  It could be any one of the
 500 following:
 501
 502   'added'        -- FILE was added
 503   'removed'      -- FILE was deleted
 504   'modified'     -- FILE's contents or its attributes were modified
 505   'renamed-from' -- a file was renamed whose old name was FILE
 506   'renamed-to'   -- a file was renamed and its new name is FILE
 507
 508 FILE is the name of the file whose event is being reported.
 509
 510 Note that some networked filesystems, such as Samba-mounted Unix
 511 volumes, might not send notifications about file changes.  In these
 512 cases, this function will return a valid descriptor, but notifications
 513 will never come in.  Volumes shared from remote Windows machines do
 514 generate notifications correctly, though.  */)
 515   (Lisp_Object file, Lisp_Object filter, Lisp_Object callback)
 516 {
 517   Lisp_Object dirfn, basefn, watch_object, watch_descriptor;
 518   DWORD flags;
 519   BOOL subdirs = FALSE;
 520   struct notification *dirwatch = NULL;
 521   Lisp_Object lisp_errstr;
 522   char *errstr;
 523
 524   CHECK_LIST (filter);
 525
 526   /* The underlying features are available only since XP.  */
 527   if (os_subtype == OS_9X
 528       || (w32_major_version == 5 && w32_major_version < 1))
 529     {
 530       errno = ENOSYS;
 531       report_file_error ("Watching filesystem events is not supported",
 532                          Qnil);
 533     }
 534
 535   /* filenotify.el always passes us a directory, either the parent
 536      directory of a file to be watched, or the directory to be
 537      watched.  */
 538   file = Fdirectory_file_name (Fexpand_file_name (file, Qnil));
 539   if (NILP (Ffile_directory_p (file)))
 540     {
 541       /* This should only happen if we are called directly, not via
 542          filenotify.el.  If BASEFN is empty, the argument was the root
 543          directory on its drive.  */
 544       dirfn = ENCODE_FILE (Ffile_name_directory (file));
 545       basefn = ENCODE_FILE (Ffile_name_nondirectory (file));
 546       if (*SDATA (basefn) == '\0')
 547         subdirs = TRUE;
 548     }
 549   else
 550     {
 551       dirfn = ENCODE_FILE (file);
 552       basefn = Qnil;
 553     }
 554
 555   if (!NILP (Fmember (Qsubtree, filter)))
 556     subdirs = TRUE;
 557
 558   flags = filter_list_to_flags (filter);
 559
 560   dirwatch = add_watch (SSDATA (dirfn), NILP (basefn) ? "" : SSDATA (basefn),
 561                         subdirs, flags);
 562   if (!dirwatch)
 563     {
 564       DWORD err = GetLastError ();
 565
 566       errno = EINVAL;
 567       if (err)
 568         {
 569           errstr = w32_strerror (err);
 570           if (!NILP (Vlocale_coding_system))
 571             lisp_errstr
 572               = code_convert_string_norecord (build_unibyte_string (errstr),
 573                                               Vlocale_coding_system, 0);
 574           else
 575             lisp_errstr = build_string (errstr);
 576           report_file_error ("Cannot watch file",
 577                              Fcons (lisp_errstr, Fcons (file, Qnil)));
 578         }
 579       else
 580         report_file_error ("Cannot watch file", Fcons (file, Qnil));
 581     }
 582   /* Store watch object in watch list. */
 583   watch_descriptor = make_pointer_integer (dirwatch);
 584   watch_object = Fcons (watch_descriptor, callback);
 585   watch_list = Fcons (watch_object, watch_list);
 586
 587   return watch_descriptor;
 588 }
 589
 590 DEFUN ("w32notify-rm-watch", Fw32notify_rm_watch,
 591        Sw32notify_rm_watch, 1, 1, 0,
 592        doc: /* Remove an existing watch specified by its WATCH-DESCRIPTOR.
 593
 594 WATCH-DESCRIPTOR should be an object returned by `w32notify-add-watch'.  */)
 595      (Lisp_Object watch_descriptor)
 596 {
 597   Lisp_Object watch_object;
 598   struct notification *dirwatch;
 599   int status = -1;
 600
 601   /* Remove the watch object from watch list.  Do this before freeing
 602      the object, do that even if we fail to free it, watch_list is
 603      kept free of junk.  */
 604   watch_object = Fassoc (watch_descriptor, watch_list);
 605   if (!NILP (watch_object))
 606     {
 607       watch_list = Fdelete (watch_object, watch_list);
 608       dirwatch = (struct notification *)XINTPTR (watch_descriptor);
 609       if (w32_valid_pointer_p (dirwatch, sizeof(struct notification)))
 610         status = remove_watch (dirwatch);
 611     }
 612
 613   if (status == -1)
 614     report_file_error ("Invalid watch descriptor", Fcons (watch_descriptor,
 615                                                           Qnil));
 616
 617   return Qnil;
 618 }
 619
 620 Lisp_Object
 621 w32_get_watch_object (void *desc)
 622 {
 623   Lisp_Object descriptor = make_pointer_integer (desc);
 624
 625   /* This is called from the input queue handling code, inside a
 626      critical section, so we cannot possibly QUIT if watch_list is not
 627      in the right condition.  */
 628   return NILP (watch_list) ? Qnil : assoc_no_quit (descriptor, watch_list);
 629 }
 630
 631 void
 632 globals_of_w32notify (void)
 633 {
 634   watch_list = Qnil;
 635 }
 636
 637 void
 638 syms_of_w32notify (void)
 639 {
 640   DEFSYM (Qfile_name, "file-name");
 641   DEFSYM (Qdirectory_name, "directory-name");
 642   DEFSYM (Qattributes, "attributes");
 643   DEFSYM (Qlast_write_time, "last-write-time");
 644   DEFSYM (Qlast_access_time, "last-access-time");
 645   DEFSYM (Qcreation_time, "creation-time");
 646   DEFSYM (Qsecurity_desc, "security-desc");
 647   DEFSYM (Qsubtree, "subtree");
 648
 649   defsubr (&Sw32notify_add_watch);
 650   defsubr (&Sw32notify_rm_watch);
 651
 652   staticpro (&watch_list);
 653
 654   Fprovide (intern_c_string ("w32notify"), Qnil);
 655 }