/* Filesystem notifications support for GNU Emacs on the Microsoft Windows API. Copyright (C) 2012-2023 Free Software Foundation, Inc. Author: Eli Zaretskii This file is part of GNU Emacs. GNU Emacs is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. GNU Emacs is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with GNU Emacs. If not, see . */ /* Design overview: For each watch request, we launch a separate worker thread. The worker thread runs the watch_worker function, which issues an asynchronous call to ReadDirectoryChangesW, and then calls WaitForSingleObjectEx to wait that an event be signaled to terminate the thread. Waiting with WaitForSingleObjectEx puts the thread in an "alertable" state, so it wakes up when either (a) the call to ReadDirectoryChangesW completes, or (b) the main thread instructs the worker thread to terminate by signaling an event, see below. When the ReadDirectoryChangesW call completes, its completion routine watch_completion is automatically called. watch_completion stashes the received file events in a linked list used to communicate them to the main thread (using a critical section, so that several threads could alter the same linked list), posts a special message, WM_EMACS_FILENOTIFY, to the Emacs's message queue, and returns. That causes the WaitForSingleObjectEx function call inside watch_worker to return, but the thread won't terminate until the event telling to do so will be signaled. The completion routine then issues another call to ReadDirectoryChangesW as quickly as possible. (Except when it does not, see below.) In a GUI session, the WM_EMACS_FILENOTIFY message posted to the message queue gets dispatched to the main Emacs window procedure, which queues it for processing by w32_read_socket. When w32_read_socket sees this message, it accesses the linked list with file notifications (using a critical section), extracts the information, converts it to a series of FILE_NOTIFY_EVENT events, and stuffs them into the input event queue to be processed by keyboard.c input machinery (read_char via a call to kbd_buffer_get_event). In a non-GUI session, we send the WM_EMACS_FILENOTIFY message to the main (a.k.a. "Lisp") thread instead, since there are no window procedures in console programs. That message wakes up MsgWaitForMultipleObjects inside sys_select, which then signals to its caller that some keyboard input is available. This causes w32_console_read_socket to be called, which accesses the linked list with file notifications and stuffs them into the input event queue for keyboard.c to process. When the FILE_NOTIFY_EVENT event is processed by keyboard.c's kbd_buffer_get_event, it is converted to a Lispy event that can be bound to a command. The default binding is file-notify-handle-event, defined on subr.el. Routines w32_read_socket or w32_console_read_socket process notifications sets as long as some are available. When the watch is removed by a call to w32notify-rm-watch, the main thread requests that the worker thread terminates by signaling the appropriate event and queuing an APC for the worker thread. The APC specifies the watch_end function to be called. watch_end calls CancelIo on the outstanding ReadDirectoryChangesW call. When watch_end returns, the watch_completion function is called one last time with the ERROR_OPERATION_ABORTED status, which causes it to clean up and set a flag telling watch_worker to exit without issuing another ReadDirectoryChangesW call. Since watch_worker is the thread procedure of the worker thread, exiting it causes the thread to exit. The main thread waits for some time for the worker thread to exit, and if it doesn't, terminates it forcibly. */ #define DEFER_MS_W32_H #include #include #include /* Include CRT headers *before* ms-w32.h. */ #include #include #include "lisp.h" #include "w32term.h" /* for enter_crit/leave_crit and WM_EMACS_FILENOTIFY */ #include "w32common.h" /* for OS version data */ #include "w32.h" /* for w32_strerror */ #include "coding.h" #include "keyboard.h" #include "frame.h" /* needed by termhooks.h */ #include "termhooks.h" /* for FILE_NOTIFY_EVENT */ #define DIRWATCH_BUFFER_SIZE 16384 #define DIRWATCH_SIGNATURE 0x01233210 struct notification { BYTE *buf; /* buffer for ReadDirectoryChangesW */ OVERLAPPED *io_info; /* the OVERLAPPED structure for async I/O */ BOOL subtree; /* whether to watch subdirectories */ DWORD filter; /* bit mask for events to watch */ char *watchee; /* the file we are interested in, UTF-8 encoded */ HANDLE dir; /* handle to the watched directory */ HANDLE thr; /* handle to the thread that watches */ HANDLE terminate; /* event signaling the thread to terminate */ unsigned signature; }; /* Used for communicating notifications to the main thread. */ struct notifications_set *notifications_set_head; static Lisp_Object watch_list; /* Signal to the main thread that we have file notifications for it to process. */ static void send_notifications (struct notifications_set *ns) { struct frame *f = SELECTED_FRAME (); /* We add the current notification set to the linked list. Use the critical section to make sure only one thread will access the linked list. */ enter_crit (); ns->next = notifications_set_head; ns->prev = notifications_set_head->prev; ns->prev->next = ns; notifications_set_head->prev = ns; leave_crit(); /* If PostMessage fails, the message queue is full. If that happens, the last thing they will worry about is file notifications. So we effectively discard the notification in that case. */ if (FRAME_TERMCAP_P (f)) /* We send the message to the main (a.k.a. "Lisp") thread, where it will wake up MsgWaitForMultipleObjects inside sys_select, causing it to report that there's some keyboard input available. This will in turn cause w32_console_read_socket to be called, which will pick up the file notifications. */ PostThreadMessage (dwMainThreadId, WM_EMACS_FILENOTIFY, 0, 0); else if (FRAME_W32_P (f)) PostMessage (FRAME_W32_WINDOW (f), WM_EMACS_FILENOTIFY, 0, 0); /* When we are running in batch mode, there's no one to send a message, so we just signal the data is available and hope sys_select will be called soon and will read the data. */ #if 0 else if (FRAME_INITIAL_P (f) && noninteractive) ; #endif } /* An APC routine to cancel outstanding directory watch. Invoked by the main thread via QueueUserAPC. This is needed because only the thread that issued the ReadDirectoryChangesW call can call CancelIo to cancel that. (CancelIoEx is only available since Vista, so we cannot use it on XP.) */ VOID CALLBACK watch_end (ULONG_PTR); VOID CALLBACK watch_end (ULONG_PTR arg) { HANDLE hdir = (HANDLE)arg; if (hdir && hdir != INVALID_HANDLE_VALUE) CancelIo (hdir); } /* A completion routine (a.k.a. "APC function") for handling events read by ReadDirectoryChangesW. Called by the OS when the thread which issued the asynchronous ReadDirectoryChangesW call is in the "alertable state", i.e. waiting inside SleepEx call. */ VOID CALLBACK watch_completion (DWORD, DWORD, OVERLAPPED *); VOID CALLBACK watch_completion (DWORD status, DWORD bytes_ret, OVERLAPPED *io_info) { struct notification *dirwatch; DWORD _bytes; struct notifications_set *ns = NULL; BOOL terminate = FALSE; /* Who knows what happened? Perhaps the OVERLAPPED structure was freed by someone already? In any case, we cannot do anything with this request, so just punt and skip it. FIXME: should we raise the 'terminate' flag in this case? */ if (!io_info) { DebPrint(("watch_completion: io_info is null.\n")); return; } /* We have a pointer to our dirwatch structure conveniently stashed away in the hEvent member of the OVERLAPPED struct. According to MSDN documentation of ReadDirectoryChangesW: "The hEvent member of the OVERLAPPED structure is not used by the system, so you can use it yourself." */ dirwatch = (struct notification *)io_info->hEvent; if (status == ERROR_OPERATION_ABORTED) { /* We've been called because the main thread told us to issue CancelIo on the directory we watch, and watch_end did so. We must exit, without issuing another call to ReadDirectoryChangesW. */ return; } /* We allocate a new set of notifications to be linked to the linked list of notifications set. This will be processed by Emacs event loop in the main thread. We need to duplicate the notifications buffer, but not the dirwatch structure. */ /* Implementation note: In general, allocating memory in non-main threads is a no-no in Emacs. We certainly cannot call xmalloc and friends, because it can longjmp when allocation fails, which will crash Emacs because the jmp_buf is set up to a location on the main thread's stack. However, we can call 'malloc' directly, since that is redirected to HeapAlloc that uses our private heap, see w32heap.c, and that is thread-safe. */ ns = malloc (sizeof(struct notifications_set)); if (ns) { memset (ns, 0, sizeof(struct notifications_set)); ns->notifications = malloc (bytes_ret); if (ns->notifications) { memcpy (ns->notifications, dirwatch->buf, bytes_ret); ns->size = bytes_ret; ns->desc = dirwatch; } else { free (ns); ns = NULL; } } if (ns == NULL) DebPrint(("Out of memory. Notifications lost.")); /* Calling ReadDirectoryChangesW quickly to watch again for new notifications. */ if (!ReadDirectoryChangesW (dirwatch->dir, dirwatch->buf, DIRWATCH_BUFFER_SIZE, dirwatch->subtree, dirwatch->filter, &_bytes, dirwatch->io_info, watch_completion)) { DebPrint (("ReadDirectoryChangesW error: %lu\n", GetLastError ())); /* If this call fails, it means that the directory is not watchable any more. We need to terminate the worker thread. Still, we will wait until the current notifications have been sent to the main thread. */ terminate = TRUE; } if (ns) send_notifications(ns); /* If we were asked to terminate the thread, then fire the event. */ if (terminate) SetEvent(dirwatch->terminate); } /* Worker routine for the watch thread. */ static DWORD WINAPI watch_worker (LPVOID arg) { struct notification *dirwatch = (struct notification *)arg; BOOL bErr; DWORD _bytes = 0; DWORD status; if (dirwatch->dir) { bErr = ReadDirectoryChangesW (dirwatch->dir, dirwatch->buf, DIRWATCH_BUFFER_SIZE, dirwatch->subtree, dirwatch->filter, &_bytes, dirwatch->io_info, watch_completion); if (!bErr) { DebPrint (("ReadDirectoryChangesW: %lu\n", GetLastError ())); /* We cannot remove the dirwatch object from watch_list, because we are in a separate thread. For the same reason, we also cannot free memory consumed by the buffers allocated for the dirwatch object. So we close the directory handle, but do not free the object itself or its buffers. We also don't touch the signature. This way, remove_watch can still identify the object, remove it, and free its memory. */ CloseHandle (dirwatch->dir); dirwatch->dir = NULL; return 1; } } do { status = WaitForSingleObjectEx(dirwatch->terminate, INFINITE, TRUE); } while (status == WAIT_IO_COMPLETION); /* The thread is about to terminate, so we clean up the dir handle. */ CloseHandle (dirwatch->dir); dirwatch->dir = NULL; return 0; } /* Launch a thread to watch changes to FILE in a directory open on handle HDIR. */ static struct notification * start_watching (const char *file, HANDLE hdir, BOOL subdirs, DWORD flags) { struct notification *dirwatch = xzalloc (sizeof (struct notification)); dirwatch->signature = DIRWATCH_SIGNATURE; dirwatch->buf = xmalloc (DIRWATCH_BUFFER_SIZE); dirwatch->io_info = xzalloc (sizeof(OVERLAPPED)); /* Stash a pointer to dirwatch structure for use by the completion routine. According to MSDN documentation of ReadDirectoryChangesW: "The hEvent member of the OVERLAPPED structure is not used by the system, so you can use it yourself." */ dirwatch->io_info->hEvent = dirwatch; dirwatch->subtree = subdirs; dirwatch->filter = flags; dirwatch->watchee = xstrdup (file); dirwatch->terminate = CreateEvent(NULL, FALSE, FALSE, NULL); dirwatch->dir = hdir; /* See w32proc.c where it calls CreateThread for the story behind the 2nd and 5th argument in the call to CreateThread. */ dirwatch->thr = CreateThread (NULL, 64 * 1024, watch_worker, (void *)dirwatch, 0x00010000, NULL); if (!dirwatch->thr) { CloseHandle(dirwatch->terminate); xfree (dirwatch->buf); xfree (dirwatch->io_info); xfree (dirwatch->watchee); xfree (dirwatch); } return dirwatch; } /* Called from the main thread to start watching FILE in PARENT_DIR, subject to FLAGS. If SUBDIRS is TRUE, watch the subdirectories of PARENT_DIR as well. Value is a pointer to 'struct notification' used by the thread that watches the changes. */ static struct notification * add_watch (const char *parent_dir, const char *file, BOOL subdirs, DWORD flags) { HANDLE hdir; struct notification *dirwatch = NULL; if (!file) return NULL; /* Do not follow symlinks, so that the caller could watch symlink files. */ DWORD crflags = FILE_FLAG_BACKUP_SEMANTICS | FILE_FLAG_OVERLAPPED; if (symlinks_supported (parent_dir)) crflags |= FILE_FLAG_OPEN_REPARSE_POINT; if (w32_unicode_filenames) { wchar_t dir_w[MAX_PATH], file_w[MAX_PATH]; filename_to_utf16 (parent_dir, dir_w); if (*file) filename_to_utf16 (file, file_w); else file_w[0] = 0; hdir = CreateFileW (dir_w, FILE_LIST_DIRECTORY, /* FILE_SHARE_DELETE doesn't preclude other processes from deleting files inside parent_dir. */ FILE_SHARE_READ|FILE_SHARE_WRITE|FILE_SHARE_DELETE, NULL, OPEN_EXISTING, crflags, NULL); } else { char dir_a[MAX_PATH], file_a[MAX_PATH]; filename_to_ansi (parent_dir, dir_a); if (*file) filename_to_ansi (file, file_a); else file_a[0] = '\0'; hdir = CreateFileA (dir_a, FILE_LIST_DIRECTORY, FILE_SHARE_READ|FILE_SHARE_WRITE|FILE_SHARE_DELETE, NULL, OPEN_EXISTING, crflags, NULL); } if (hdir == INVALID_HANDLE_VALUE) return NULL; if ((dirwatch = start_watching (file, hdir, subdirs, flags)) == NULL) { CloseHandle (hdir); dirwatch->dir = NULL; } return dirwatch; } /* Stop watching a directory specified by a pointer to its dirwatch object. */ static int remove_watch (struct notification *dirwatch) { if (dirwatch && dirwatch->signature == DIRWATCH_SIGNATURE) { int i; BOOL status; DWORD exit_code = 0, err = 0; /* Only the thread that issued the outstanding I/O call can call CancelIo on it. (CancelIoEx is available only since Vista.) So we need to queue an APC for the worker thread telling it to terminate. */ if (!QueueUserAPC (watch_end, dirwatch->thr, (ULONG_PTR)dirwatch->dir)) DebPrint (("QueueUserAPC failed (%lu)!\n", GetLastError ())); /* We also signal the thread that it can terminate. */ SetEvent(dirwatch->terminate); /* Wait for the thread to exit. FIXME: is there a better method that is not overly complex? */ for (i = 0; i < 50; i++) { if (!((status = GetExitCodeThread (dirwatch->thr, &exit_code)) && exit_code == STILL_ACTIVE)) break; Sleep (10); } if ((status == FALSE && (err = GetLastError ()) == ERROR_INVALID_HANDLE) || exit_code == STILL_ACTIVE) { if (!(status == FALSE && err == ERROR_INVALID_HANDLE)) { DebPrint(("Forcing thread termination.\n")); TerminateThread (dirwatch->thr, 0); if (dirwatch->dir) CloseHandle (dirwatch->dir); } } /* Clean up. */ if (dirwatch->thr) { CloseHandle (dirwatch->thr); dirwatch->thr = NULL; } CloseHandle(dirwatch->terminate); xfree (dirwatch->buf); xfree (dirwatch->io_info); xfree (dirwatch->watchee); xfree (dirwatch); return 0; } else { DebPrint (("Unknown dirwatch object!\n")); return -1; } } static DWORD filter_list_to_flags (Lisp_Object filter_list) { DWORD flags = 0; if (NILP (filter_list)) return flags; if (!NILP (Fmember (Qfile_name, filter_list))) flags |= FILE_NOTIFY_CHANGE_FILE_NAME; if (!NILP (Fmember (Qdirectory_name, filter_list))) flags |= FILE_NOTIFY_CHANGE_DIR_NAME; if (!NILP (Fmember (Qattributes, filter_list))) flags |= FILE_NOTIFY_CHANGE_ATTRIBUTES; if (!NILP (Fmember (Qsize, filter_list))) flags |= FILE_NOTIFY_CHANGE_SIZE; if (!NILP (Fmember (Qlast_write_time, filter_list))) flags |= FILE_NOTIFY_CHANGE_LAST_WRITE; if (!NILP (Fmember (Qlast_access_time, filter_list))) flags |= FILE_NOTIFY_CHANGE_LAST_ACCESS; if (!NILP (Fmember (Qcreation_time, filter_list))) flags |= FILE_NOTIFY_CHANGE_CREATION; if (!NILP (Fmember (Qsecurity_desc, filter_list))) flags |= FILE_NOTIFY_CHANGE_SECURITY; return flags; } DEFUN ("w32notify-add-watch", Fw32notify_add_watch, Sw32notify_add_watch, 3, 3, 0, doc: /* Add a watch for filesystem events pertaining to FILE. This arranges for filesystem events pertaining to FILE to be reported to Emacs. Use `w32notify-rm-watch' to cancel the watch. Value is a descriptor for the added watch. If the file cannot be watched for some reason, this function signals a `file-error' error. FILTER is a list of conditions for reporting an event. It can include the following symbols: `file-name' -- report file creation, deletion, or renaming `directory-name' -- report directory creation, deletion, or renaming `attributes' -- report changes in attributes `size' -- report changes in file-size `last-write-time' -- report changes in last-write time `last-access-time' -- report changes in last-access time `creation-time' -- report changes in creation time `security-desc' -- report changes in security descriptor If FILE is a directory, and FILTER includes `subtree', then all the subdirectories will also be watched and changes in them reported. When any event happens that satisfies the conditions specified by FILTER, Emacs will call the CALLBACK function passing it a single argument EVENT, which is of the form (DESCRIPTOR ACTION FILE) DESCRIPTOR is the same object as the one returned by this function. ACTION is the description of the event. It could be any one of the following: `added' -- FILE was added `removed' -- FILE was deleted `modified' -- FILE's contents or its attributes were modified `renamed-from' -- a file was renamed whose old name was FILE `renamed-to' -- a file was renamed and its new name is FILE FILE is the name of the file whose event is being reported. Note that some networked filesystems, such as Samba-mounted Unix volumes, might not send notifications about file changes. In these cases, this function will return a valid descriptor, but notifications will never come in. Volumes shared from remote Windows machines do generate notifications correctly, though. */) (Lisp_Object file, Lisp_Object filter, Lisp_Object callback) { Lisp_Object dirfn, basefn, watch_object, watch_descriptor; DWORD flags; BOOL subdirs = FALSE; struct notification *dirwatch = NULL; Lisp_Object lisp_errstr; char *errstr; CHECK_LIST (filter); /* The underlying features are available only since XP. */ if (os_subtype == OS_SUBTYPE_9X || (w32_major_version == 5 && w32_minor_version < 1)) { errno = ENOSYS; report_file_notify_error ("Watching filesystem events is not supported", Qnil); } /* filenotify.el always passes us a directory, either the parent directory of a file to be watched, or the directory to be watched. */ file = Fdirectory_file_name (Fexpand_file_name (file, Qnil)); if (NILP (Ffile_directory_p (file))) { /* This should only happen if we are called directly, not via filenotify.el. If BASEFN is empty, the argument was the root directory on its drive. */ dirfn = ENCODE_FILE (Ffile_name_directory (file)); basefn = ENCODE_FILE (Ffile_name_nondirectory (file)); if (*SDATA (basefn) == '\0') subdirs = TRUE; } else { dirfn = ENCODE_FILE (file); basefn = Qnil; } if (!NILP (Fmember (Qsubtree, filter))) subdirs = TRUE; flags = filter_list_to_flags (filter); dirwatch = add_watch (SSDATA (dirfn), NILP (basefn) ? "" : SSDATA (basefn), subdirs, flags); if (!dirwatch) { DWORD err = GetLastError (); errno = EINVAL; if (err) { errstr = w32_strerror (err); if (!NILP (Vlocale_coding_system)) lisp_errstr = code_convert_string_norecord (build_unibyte_string (errstr), Vlocale_coding_system, 0); else lisp_errstr = build_string (errstr); report_file_notify_error ("Cannot watch file", Fcons (lisp_errstr, Fcons (file, Qnil))); } else report_file_notify_error ("Cannot watch file", Fcons (file, Qnil)); } /* Store watch object in watch list. */ watch_descriptor = make_mint_ptr (dirwatch); watch_object = Fcons (watch_descriptor, callback); watch_list = Fcons (watch_object, watch_list); return watch_descriptor; } DEFUN ("w32notify-rm-watch", Fw32notify_rm_watch, Sw32notify_rm_watch, 1, 1, 0, doc: /* Remove an existing watch specified by its WATCH-DESCRIPTOR. WATCH-DESCRIPTOR should be an object returned by `w32notify-add-watch'. */) (Lisp_Object watch_descriptor) { Lisp_Object watch_object; struct notification *dirwatch; int status = -1; /* Remove the watch object from watch list. Do this before freeing the object, do that even if we fail to free it, watch_list is kept free of junk. */ watch_object = Fassoc (watch_descriptor, watch_list, Qnil); if (!NILP (watch_object)) { watch_list = Fdelete (watch_object, watch_list); dirwatch = (struct notification *)xmint_pointer (watch_descriptor); if (w32_valid_pointer_p (dirwatch, sizeof(struct notification))) status = remove_watch (dirwatch); } if (status == -1) report_file_notify_error ("Invalid watch descriptor", Fcons (watch_descriptor, Qnil)); return Qnil; } Lisp_Object w32_get_watch_object (void *desc) { Lisp_Object descriptor = make_mint_ptr (desc); /* This is called from the input queue handling code, inside a critical section, so we cannot possibly quit if watch_list is not in the right condition. */ return NILP (watch_list) ? Qnil : assoc_no_quit (descriptor, watch_list); } DEFUN ("w32notify-valid-p", Fw32notify_valid_p, Sw32notify_valid_p, 1, 1, 0, doc: /* Check a watch specified by its WATCH-DESCRIPTOR for validity. WATCH-DESCRIPTOR should be an object returned by `w32notify-add-watch'. A watch can become invalid if the directory it watches is deleted, or if the watcher thread exits abnormally for any other reason. Removing the watch by calling `w32notify-rm-watch' also makes it invalid. */) (Lisp_Object watch_descriptor) { Lisp_Object watch_object = Fassoc (watch_descriptor, watch_list, Qnil); if (!NILP (watch_object)) { struct notification *dirwatch = (struct notification *)xmint_pointer (watch_descriptor); if (w32_valid_pointer_p (dirwatch, sizeof(struct notification)) && dirwatch->dir != NULL) return Qt; } return Qnil; } void globals_of_w32notify (void) { watch_list = Qnil; } void syms_of_w32notify (void) { DEFSYM (Qfile_name, "file-name"); DEFSYM (Qdirectory_name, "directory-name"); DEFSYM (Qattributes, "attributes"); DEFSYM (Qlast_write_time, "last-write-time"); DEFSYM (Qlast_access_time, "last-access-time"); DEFSYM (Qcreation_time, "creation-time"); DEFSYM (Qsecurity_desc, "security-desc"); DEFSYM (Qsubtree, "subtree"); defsubr (&Sw32notify_add_watch); defsubr (&Sw32notify_rm_watch); defsubr (&Sw32notify_valid_p); staticpro (&watch_list); Fprovide (intern_c_string ("w32notify"), Qnil); }