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_path.h"
   9 #include "base/file_util.h"
  10 #include "base/logging.h"
  11 #include "base/memory/ref_counted.h"
  12 #include "base/message_loop_proxy.h"
  13 #include "base/time.h"
  14 #include "base/win/object_watcher.h"
  15
  16 namespace base {
  17 namespace files {
  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       : delegate_(NULL),
  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                      FilePathWatcher::Delegate* delegate) 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);
  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   // Delegate to notify upon changes.
  65   scoped_refptr<FilePathWatcher::Delegate> delegate_;
  66
  67   // Path we're supposed to watch (passed to delegate).
  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   base::Time last_modified_;
  82
  83   // The time at which we processed the first notification with the
  84   // |last_modified_| time stamp.
  85   base::Time first_notification_;
  86
  87   DISALLOW_COPY_AND_ASSIGN(FilePathWatcherImpl);
  88 };
  89
  90 bool FilePathWatcherImpl::Watch(const FilePath& path,
  91                                 bool recursive,
  92                                 FilePathWatcher::Delegate* delegate) {
  93   DCHECK(target_.value().empty());  // Can only watch one path.
  94
  95   set_message_loop(base::MessageLoopProxy::current());
  96   delegate_ = delegate;
  97   target_ = path;
  98   recursive_watch_ = recursive;
  99   MessageLoop::current()->AddDestructionObserver(this);
 100
 101   if (!UpdateWatch())
 102     return false;
 103
 104   watcher_.StartWatching(handle_, this);
 105
 106   return true;
 107 }
 108
 109 void FilePathWatcherImpl::Cancel() {
 110   if (!delegate_) {
 111     // Watch was never called, or the |message_loop_| has already quit.
 112     set_cancelled();
 113     return;
 114   }
 115
 116   // Switch to the file thread if necessary so we can stop |watcher_|.
 117   if (!message_loop()->BelongsToCurrentThread()) {
 118     message_loop()->PostTask(FROM_HERE,
 119                              base::Bind(&FilePathWatcher::CancelWatch,
 120                                         make_scoped_refptr(this)));
 121   } else {
 122     CancelOnMessageLoopThread();
 123   }
 124 }
 125
 126 void FilePathWatcherImpl::CancelOnMessageLoopThread() {
 127   set_cancelled();
 128
 129   if (handle_ != INVALID_HANDLE_VALUE)
 130     DestroyWatch();
 131
 132   if (delegate_) {
 133     MessageLoop::current()->RemoveDestructionObserver(this);
 134     delegate_ = NULL;
 135   }
 136 }
 137
 138 void FilePathWatcherImpl::WillDestroyCurrentMessageLoop() {
 139   CancelOnMessageLoopThread();
 140 }
 141
 142 void FilePathWatcherImpl::OnObjectSignaled(HANDLE object) {
 143   DCHECK(object == handle_);
 144   // Make sure we stay alive through the body of this function.
 145   scoped_refptr<FilePathWatcherImpl> keep_alive(this);
 146
 147   if (!UpdateWatch()) {
 148     delegate_->OnFilePathError(target_);
 149     return;
 150   }
 151
 152   // Check whether the event applies to |target_| and notify the delegate.
 153   base::PlatformFileInfo file_info;
 154   bool file_exists = file_util::GetFileInfo(target_, &file_info);
 155   if (file_exists && (last_modified_.is_null() ||
 156       last_modified_ != file_info.last_modified)) {
 157     last_modified_ = file_info.last_modified;
 158     first_notification_ = base::Time::Now();
 159     delegate_->OnFilePathChanged(target_);
 160   } else if (file_exists && !first_notification_.is_null()) {
 161     // The target's last modification time is equal to what's on record. This
 162     // means that either an unrelated event occurred, or the target changed
 163     // again (file modification times only have a resolution of 1s). Comparing
 164     // file modification times against the wall clock is not reliable to find
 165     // out whether the change is recent, since this code might just run too
 166     // late. Moreover, there's no guarantee that file modification time and wall
 167     // clock times come from the same source.
 168     //
 169     // Instead, the time at which the first notification carrying the current
 170     // |last_notified_| time stamp is recorded. Later notifications that find
 171     // the same file modification time only need to be forwarded until wall
 172     // clock has advanced one second from the initial notification. After that
 173     // interval, client code is guaranteed to having seen the current revision
 174     // of the file.
 175     if (base::Time::Now() - first_notification_ >
 176         base::TimeDelta::FromSeconds(1)) {
 177       // Stop further notifications for this |last_modification_| time stamp.
 178       first_notification_ = base::Time();
 179     }
 180     delegate_->OnFilePathChanged(target_);
 181   } else if (!file_exists && !last_modified_.is_null()) {
 182     last_modified_ = base::Time();
 183     delegate_->OnFilePathChanged(target_);
 184   }
 185
 186   // The watch may have been cancelled by the callback.
 187   if (handle_ != INVALID_HANDLE_VALUE)
 188     watcher_.StartWatching(handle_, this);
 189 }
 190
 191 // static
 192 bool FilePathWatcherImpl::SetupWatchHandle(const FilePath& dir,
 193                                            bool recursive,
 194                                            HANDLE* handle) {
 195   *handle = FindFirstChangeNotification(
 196       dir.value().c_str(),
 197       recursive,
 198       FILE_NOTIFY_CHANGE_FILE_NAME | FILE_NOTIFY_CHANGE_SIZE |
 199       FILE_NOTIFY_CHANGE_LAST_WRITE | FILE_NOTIFY_CHANGE_DIR_NAME |
 200       FILE_NOTIFY_CHANGE_ATTRIBUTES | FILE_NOTIFY_CHANGE_SECURITY);
 201   if (*handle != INVALID_HANDLE_VALUE) {
 202     // Make sure the handle we got points to an existing directory. It seems
 203     // that windows sometimes hands out watches to directories that are
 204     // about to go away, but doesn't sent notifications if that happens.
 205     if (!file_util::DirectoryExists(dir)) {
 206       FindCloseChangeNotification(*handle);
 207       *handle = INVALID_HANDLE_VALUE;
 208     }
 209     return true;
 210   }
 211
 212   // If FindFirstChangeNotification failed because the target directory
 213   // doesn't exist, access is denied (happens if the file is already gone but
 214   // there are still handles open), or the target is not a directory, try the
 215   // immediate parent directory instead.
 216   DWORD error_code = GetLastError();
 217   if (error_code != ERROR_FILE_NOT_FOUND &&
 218       error_code != ERROR_PATH_NOT_FOUND &&
 219       error_code != ERROR_ACCESS_DENIED &&
 220       error_code != ERROR_SHARING_VIOLATION &&
 221       error_code != ERROR_DIRECTORY) {
 222     using ::operator<<; // Pick the right operator<< below.
 223     DPLOG(ERROR) << "FindFirstChangeNotification failed for "
 224                  << dir.value();
 225     return false;
 226   }
 227
 228   return true;
 229 }
 230
 231 bool FilePathWatcherImpl::UpdateWatch() {
 232   if (handle_ != INVALID_HANDLE_VALUE)
 233     DestroyWatch();
 234
 235   base::PlatformFileInfo file_info;
 236   if (file_util::GetFileInfo(target_, &file_info)) {
 237     last_modified_ = file_info.last_modified;
 238     first_notification_ = base::Time::Now();
 239   }
 240
 241   // Start at the target and walk up the directory chain until we succesfully
 242   // create a watch handle in |handle_|. |child_dirs| keeps a stack of child
 243   // directories stripped from target, in reverse order.
 244   std::vector<FilePath> child_dirs;
 245   FilePath watched_path(target_);
 246   while (true) {
 247     if (!SetupWatchHandle(watched_path, recursive_watch_, &handle_))
 248       return false;
 249
 250     // Break if a valid handle is returned. Try the parent directory otherwise.
 251     if (handle_ != INVALID_HANDLE_VALUE)
 252       break;
 253
 254     // Abort if we hit the root directory.
 255     child_dirs.push_back(watched_path.BaseName());
 256     FilePath parent(watched_path.DirName());
 257     if (parent == watched_path) {
 258       DLOG(ERROR) << "Reached the root directory";
 259       return false;
 260     }
 261     watched_path = parent;
 262   }
 263
 264   // At this point, handle_ is valid. However, the bottom-up search that the
 265   // above code performs races against directory creation. So try to walk back
 266   // down and see whether any children appeared in the mean time.
 267   while (!child_dirs.empty()) {
 268     watched_path = watched_path.Append(child_dirs.back());
 269     child_dirs.pop_back();
 270     HANDLE temp_handle = INVALID_HANDLE_VALUE;
 271     if (!SetupWatchHandle(watched_path, recursive_watch_, &temp_handle))
 272       return false;
 273     if (temp_handle == INVALID_HANDLE_VALUE)
 274       break;
 275     FindCloseChangeNotification(handle_);
 276     handle_ = temp_handle;
 277   }
 278
 279   return true;
 280 }
 281
 282 void FilePathWatcherImpl::DestroyWatch() {
 283   watcher_.StopWatching();
 284   FindCloseChangeNotification(handle_);
 285   handle_ = INVALID_HANDLE_VALUE;
 286 }
 287
 288 }  // namespace
 289
 290 FilePathWatcher::FilePathWatcher() {
 291   impl_ = new FilePathWatcherImpl();
 292 }
 293
 294 }  // namespace files
 295 }  // namespace base