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