base/files/file_path_watcher_win.cc

   1 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "base/files/file_path_watcher.h"
   6
   7 #include "base/bind.h"
   8 #include "base/files/file.h"
   9 #include "base/files/file_path.h"
  10 #include "base/files/file_util.h"
  11 #include "base/logging.h"
  12 #include "base/memory/ref_counted.h"
  13 #include "base/message_loop/message_loop_proxy.h"
  14 #include "base/profiler/scoped_tracker.h"
  15 #include "base/time/time.h"
  16 #include "base/win/object_watcher.h"
  17
  18 namespace base {
  19
  20 namespace {
  21
  22 class FilePathWatcherImpl : public FilePathWatcher::PlatformDelegate,
  23                             public base::win::ObjectWatcher::Delegate,
  24                             public MessageLoop::DestructionObserver {
  25  public:
  26   FilePathWatcherImpl()
  27       : handle_(INVALID_HANDLE_VALUE),
  28         recursive_watch_(false) {}
  29
  30   // FilePathWatcher::PlatformDelegate overrides.
  31   virtual bool Watch(const FilePath& path,
  32                      bool recursive,
  33                      const FilePathWatcher::Callback& callback) override;
  34   virtual void Cancel() override;
  35
  36   // Deletion of the FilePathWatcher will call Cancel() to dispose of this
  37   // object in the right thread. This also observes destruction of the required
  38   // cleanup thread, in case it quits before Cancel() is called.
  39   virtual void WillDestroyCurrentMessageLoop() override;
  40
  41   // Callback from MessageLoopForIO.
  42   virtual void OnObjectSignaled(HANDLE object) override;
  43
  44  private:
  45   virtual ~FilePathWatcherImpl() {}
  46
  47   // Setup a watch handle for directory |dir|. Set |recursive| to true to watch
  48   // the directory sub trees. Returns true if no fatal error occurs. |handle|
  49   // will receive the handle value if |dir| is watchable, otherwise
  50   // INVALID_HANDLE_VALUE.
  51   static bool SetupWatchHandle(const FilePath& dir,
  52                                bool recursive,
  53                                HANDLE* handle) WARN_UNUSED_RESULT;
  54
  55   // (Re-)Initialize the watch handle.
  56   bool UpdateWatch() WARN_UNUSED_RESULT;
  57
  58   // Destroy the watch handle.
  59   void DestroyWatch();
  60
  61   // Cleans up and stops observing the |message_loop_| thread.
  62   void CancelOnMessageLoopThread() override;
  63
  64   // Callback to notify upon changes.
  65   FilePathWatcher::Callback callback_;
  66
  67   // Path we're supposed to watch (passed to callback).
  68   FilePath target_;
  69
  70   // Handle for FindFirstChangeNotification.
  71   HANDLE handle_;
  72
  73   // ObjectWatcher to watch handle_ for events.
  74   base::win::ObjectWatcher watcher_;
  75
  76   // Set to true to watch the sub trees of the specified directory file path.
  77   bool recursive_watch_;
  78
  79   // Keep track of the last modified time of the file.  We use nulltime
  80   // to represent the file not existing.
  81   Time last_modified_;
  82
  83   // The time at which we processed the first notification with the
  84   // |last_modified_| time stamp.
  85   Time first_notification_;
  86
  87   DISALLOW_COPY_AND_ASSIGN(FilePathWatcherImpl);
  88 };
  89
  90 bool FilePathWatcherImpl::Watch(const FilePath& path,
  91                                 bool recursive,
  92                                 const FilePathWatcher::Callback& callback) {
  93   DCHECK(target_.value().empty());  // Can only watch one path.
  94
  95   set_message_loop(MessageLoopProxy::current());
  96   callback_ = callback;
  97   target_ = path;
  98   recursive_watch_ = recursive;
  99   MessageLoop::current()->AddDestructionObserver(this);
 100
 101   File::Info file_info;
 102   if (GetFileInfo(target_, &file_info)) {
 103     last_modified_ = file_info.last_modified;
 104     first_notification_ = Time::Now();
 105   }
 106
 107   if (!UpdateWatch())
 108     return false;
 109
 110   watcher_.StartWatching(handle_, this);
 111
 112   return true;
 113 }
 114
 115 void FilePathWatcherImpl::Cancel() {
 116   if (callback_.is_null()) {
 117     // Watch was never called, or the |message_loop_| has already quit.
 118     set_cancelled();
 119     return;
 120   }
 121
 122   // Switch to the file thread if necessary so we can stop |watcher_|.
 123   if (!message_loop()->BelongsToCurrentThread()) {
 124     message_loop()->PostTask(FROM_HERE,
 125                              Bind(&FilePathWatcher::CancelWatch,
 126                                   make_scoped_refptr(this)));
 127   } else {
 128     CancelOnMessageLoopThread();
 129   }
 130 }
 131
 132 void FilePathWatcherImpl::CancelOnMessageLoopThread() {
 133   DCHECK(message_loop()->BelongsToCurrentThread());
 134   set_cancelled();
 135
 136   if (handle_ != INVALID_HANDLE_VALUE)
 137     DestroyWatch();
 138
 139   if (!callback_.is_null()) {
 140     MessageLoop::current()->RemoveDestructionObserver(this);
 141     callback_.Reset();
 142   }
 143 }
 144
 145 void FilePathWatcherImpl::WillDestroyCurrentMessageLoop() {
 146   CancelOnMessageLoopThread();
 147 }
 148
 149 void FilePathWatcherImpl::OnObjectSignaled(HANDLE object) {
 150   // TODO(vadimt): Remove ScopedTracker below once crbug.com/418183 is fixed.
 151   tracked_objects::ScopedTracker tracking_profile(
 152       FROM_HERE_WITH_EXPLICIT_FUNCTION("FilePathWatcherImpl_OnObjectSignaled"));
 153
 154   DCHECK(object == handle_);
 155   // Make sure we stay alive through the body of this function.
 156   scoped_refptr<FilePathWatcherImpl> keep_alive(this);
 157
 158   if (!UpdateWatch()) {
 159     callback_.Run(target_, true /* error */);
 160     return;
 161   }
 162
 163   // Check whether the event applies to |target_| and notify the callback.
 164   File::Info file_info;
 165   bool file_exists = GetFileInfo(target_, &file_info);
 166   if (recursive_watch_) {
 167     // Only the mtime of |target_| is tracked but in a recursive watch,
 168     // some other file or directory may have changed so all notifications
 169     // are passed through. It is possible to figure out which file changed
 170     // using ReadDirectoryChangesW() instead of FindFirstChangeNotification(),
 171     // but that function is quite complicated:
 172     // http://qualapps.blogspot.com/2010/05/understanding-readdirectorychangesw.html
 173     callback_.Run(target_, false);
 174   } else if (file_exists && (last_modified_.is_null() ||
 175              last_modified_ != file_info.last_modified)) {
 176     last_modified_ = file_info.last_modified;
 177     first_notification_ = Time::Now();
 178     callback_.Run(target_, false);
 179   } else if (file_exists && last_modified_ == file_info.last_modified &&
 180              !first_notification_.is_null()) {
 181     // The target's last modification time is equal to what's on record. This
 182     // means that either an unrelated event occurred, or the target changed
 183     // again (file modification times only have a resolution of 1s). Comparing
 184     // file modification times against the wall clock is not reliable to find
 185     // out whether the change is recent, since this code might just run too
 186     // late. Moreover, there's no guarantee that file modification time and wall
 187     // clock times come from the same source.
 188     //
 189     // Instead, the time at which the first notification carrying the current
 190     // |last_notified_| time stamp is recorded. Later notifications that find
 191     // the same file modification time only need to be forwarded until wall
 192     // clock has advanced one second from the initial notification. After that
 193     // interval, client code is guaranteed to having seen the current revision
 194     // of the file.
 195     if (Time::Now() - first_notification_ > TimeDelta::FromSeconds(1)) {
 196       // Stop further notifications for this |last_modification_| time stamp.
 197       first_notification_ = Time();
 198     }
 199     callback_.Run(target_, false);
 200   } else if (!file_exists && !last_modified_.is_null()) {
 201     last_modified_ = Time();
 202     callback_.Run(target_, false);
 203   }
 204
 205   // The watch may have been cancelled by the callback.
 206   if (handle_ != INVALID_HANDLE_VALUE)
 207     watcher_.StartWatching(handle_, this);
 208 }
 209
 210 // static
 211 bool FilePathWatcherImpl::SetupWatchHandle(const FilePath& dir,
 212                                            bool recursive,
 213                                            HANDLE* handle) {
 214   *handle = FindFirstChangeNotification(
 215       dir.value().c_str(),
 216       recursive,
 217       FILE_NOTIFY_CHANGE_FILE_NAME | FILE_NOTIFY_CHANGE_SIZE |
 218       FILE_NOTIFY_CHANGE_LAST_WRITE | FILE_NOTIFY_CHANGE_DIR_NAME |
 219       FILE_NOTIFY_CHANGE_ATTRIBUTES | FILE_NOTIFY_CHANGE_SECURITY);
 220   if (*handle != INVALID_HANDLE_VALUE) {
 221     // Make sure the handle we got points to an existing directory. It seems
 222     // that windows sometimes hands out watches to directories that are
 223     // about to go away, but doesn't sent notifications if that happens.
 224     if (!DirectoryExists(dir)) {
 225       FindCloseChangeNotification(*handle);
 226       *handle = INVALID_HANDLE_VALUE;
 227     }
 228     return true;
 229   }
 230
 231   // If FindFirstChangeNotification failed because the target directory
 232   // doesn't exist, access is denied (happens if the file is already gone but
 233   // there are still handles open), or the target is not a directory, try the
 234   // immediate parent directory instead.
 235   DWORD error_code = GetLastError();
 236   if (error_code != ERROR_FILE_NOT_FOUND &&
 237       error_code != ERROR_PATH_NOT_FOUND &&
 238       error_code != ERROR_ACCESS_DENIED &&
 239       error_code != ERROR_SHARING_VIOLATION &&
 240       error_code != ERROR_DIRECTORY) {
 241     DPLOG(ERROR) << "FindFirstChangeNotification failed for "
 242                  << dir.value();
 243     return false;
 244   }
 245
 246   return true;
 247 }
 248
 249 bool FilePathWatcherImpl::UpdateWatch() {
 250   if (handle_ != INVALID_HANDLE_VALUE)
 251     DestroyWatch();
 252
 253   // Start at the target and walk up the directory chain until we succesfully
 254   // create a watch handle in |handle_|. |child_dirs| keeps a stack of child
 255   // directories stripped from target, in reverse order.
 256   std::vector<FilePath> child_dirs;
 257   FilePath watched_path(target_);
 258   while (true) {
 259     if (!SetupWatchHandle(watched_path, recursive_watch_, &handle_))
 260       return false;
 261
 262     // Break if a valid handle is returned. Try the parent directory otherwise.
 263     if (handle_ != INVALID_HANDLE_VALUE)
 264       break;
 265
 266     // Abort if we hit the root directory.
 267     child_dirs.push_back(watched_path.BaseName());
 268     FilePath parent(watched_path.DirName());
 269     if (parent == watched_path) {
 270       DLOG(ERROR) << "Reached the root directory";
 271       return false;
 272     }
 273     watched_path = parent;
 274   }
 275
 276   // At this point, handle_ is valid. However, the bottom-up search that the
 277   // above code performs races against directory creation. So try to walk back
 278   // down and see whether any children appeared in the mean time.
 279   while (!child_dirs.empty()) {
 280     watched_path = watched_path.Append(child_dirs.back());
 281     child_dirs.pop_back();
 282     HANDLE temp_handle = INVALID_HANDLE_VALUE;
 283     if (!SetupWatchHandle(watched_path, recursive_watch_, &temp_handle))
 284       return false;
 285     if (temp_handle == INVALID_HANDLE_VALUE)
 286       break;
 287     FindCloseChangeNotification(handle_);
 288     handle_ = temp_handle;
 289   }
 290
 291   return true;
 292 }
 293
 294 void FilePathWatcherImpl::DestroyWatch() {
 295   watcher_.StopWatching();
 296   FindCloseChangeNotification(handle_);
 297   handle_ = INVALID_HANDLE_VALUE;
 298 }
 299
 300 }  // namespace
 301
 302 FilePathWatcher::FilePathWatcher() {
 303   impl_ = new FilePathWatcherImpl();
 304 }
 305
 306 }  // namespace base