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| 1 // Copyright (c) 2009 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 "chrome/browser/file_path_watcher.h" | |
| 6 | |
| 7 #include "base/file_path.h" | |
| 8 #include "base/file_util.h" | |
| 9 #include "base/logging.h" | |
| 10 #include "base/object_watcher.h" | |
| 11 #include "base/ref_counted.h" | |
| 12 #include "base/time.h" | |
| 13 | |
| 14 namespace { | |
| 15 | |
| 16 class FilePathWatcherImpl : public FilePathWatcher::PlatformDelegate, | |
| 17 public base::ObjectWatcher::Delegate { | |
| 18 public: | |
| 19 FilePathWatcherImpl() : delegate_(NULL), handle_(INVALID_HANDLE_VALUE) {} | |
| 20 | |
| 21 virtual bool Watch(const FilePath& path, FilePathWatcher::Delegate* delegate); | |
| 22 virtual void Cancel(); | |
| 23 | |
| 24 // Callback from MessageLoopForIO. | |
| 25 virtual void OnObjectSignaled(HANDLE object); | |
| 26 | |
| 27 private: | |
| 28 virtual ~FilePathWatcherImpl(); | |
| 29 | |
| 30 // Setup a watch handle for directory |dir|. Returns true if no fatal error | |
| 31 // occurs. |handle| will receive the handle value if |dir| is watchable, | |
| 32 // otherwise INVALID_HANDLE_VALUE. | |
| 33 static bool SetupWatchHandle(const FilePath& dir, HANDLE* handle) | |
| 34 WARN_UNUSED_RESULT; | |
| 35 | |
| 36 // (Re-)Initialize the watch handle. | |
| 37 bool UpdateWatch() WARN_UNUSED_RESULT; | |
| 38 | |
| 39 // Destroy the watch handle. | |
| 40 void DestroyWatch(); | |
| 41 | |
| 42 // Delegate to notify upon changes. | |
| 43 scoped_refptr<FilePathWatcher::Delegate> delegate_; | |
| 44 | |
| 45 // Path we're supposed to watch (passed to delegate). | |
| 46 FilePath target_; | |
| 47 | |
| 48 // Handle for FindFirstChangeNotification. | |
| 49 HANDLE handle_; | |
| 50 | |
| 51 // ObjectWatcher to watch handle_ for events. | |
| 52 base::ObjectWatcher watcher_; | |
| 53 | |
| 54 // Keep track of the last modified time of the file. We use nulltime | |
| 55 // to represent the file not existing. | |
| 56 base::Time last_modified_; | |
| 57 | |
| 58 // The time at which we processed the first notification with the | |
| 59 // |last_modified_| time stamp. | |
| 60 base::Time first_notification_; | |
| 61 | |
| 62 DISALLOW_COPY_AND_ASSIGN(FilePathWatcherImpl); | |
| 63 }; | |
| 64 | |
| 65 bool FilePathWatcherImpl::Watch(const FilePath& path, | |
| 66 FilePathWatcher::Delegate* delegate) { | |
| 67 DCHECK(target_.value().empty()); // Can only watch one path. | |
| 68 delegate_ = delegate; | |
| 69 target_ = path; | |
| 70 | |
| 71 if (!UpdateWatch()) | |
| 72 return false; | |
| 73 | |
| 74 watcher_.StartWatching(handle_, this); | |
| 75 | |
| 76 return true; | |
| 77 } | |
| 78 | |
| 79 void FilePathWatcherImpl::Cancel() { | |
| 80 // Switch to the file thread if necessary so we can stop |watcher_|. | |
| 81 if (!BrowserThread::CurrentlyOn(BrowserThread::FILE)) { | |
| 82 BrowserThread::PostTask(BrowserThread::FILE, FROM_HERE, | |
| 83 NewRunnableMethod(this, &FilePathWatcherImpl::Cancel)); | |
| 84 return; | |
| 85 } | |
| 86 | |
| 87 if (handle_ != INVALID_HANDLE_VALUE) | |
| 88 DestroyWatch(); | |
| 89 } | |
| 90 | |
| 91 void FilePathWatcherImpl::OnObjectSignaled(HANDLE object) { | |
| 92 DCHECK(object == handle_); | |
| 93 // Make sure we stay alive through the body of this function. | |
| 94 scoped_refptr<FilePathWatcherImpl> keep_alive(this); | |
| 95 | |
| 96 if (!UpdateWatch()) { | |
| 97 delegate_->OnError(); | |
| 98 return; | |
| 99 } | |
| 100 | |
| 101 // Check whether the event applies to |target_| and notify the delegate. | |
| 102 base::PlatformFileInfo file_info; | |
| 103 bool file_exists = file_util::GetFileInfo(target_, &file_info); | |
| 104 if (file_exists && (last_modified_.is_null() || | |
| 105 last_modified_ != file_info.last_modified)) { | |
| 106 last_modified_ = file_info.last_modified; | |
| 107 first_notification_ = base::Time::Now(); | |
| 108 delegate_->OnFilePathChanged(target_); | |
| 109 } else if (file_exists && !first_notification_.is_null()) { | |
| 110 // The target's last modification time is equal to what's on record. This | |
| 111 // means that either an unrelated event occurred, or the target changed | |
| 112 // again (file modification times only have a resolution of 1s). Comparing | |
| 113 // file modification times against the wall clock is not reliable to find | |
| 114 // out whether the change is recent, since this code might just run too | |
| 115 // late. Moreover, there's no guarantee that file modification time and wall | |
| 116 // clock times come from the same source. | |
| 117 // | |
| 118 // Instead, the time at which the first notification carrying the current | |
| 119 // |last_notified_| time stamp is recorded. Later notifications that find | |
| 120 // the same file modification time only need to be forwarded until wall | |
| 121 // clock has advanced one second from the initial notification. After that | |
| 122 // interval, client code is guaranteed to having seen the current revision | |
| 123 // of the file. | |
| 124 if (base::Time::Now() - first_notification_ > | |
| 125 base::TimeDelta::FromSeconds(1)) { | |
| 126 // Stop further notifications for this |last_modification_| time stamp. | |
| 127 first_notification_ = base::Time(); | |
| 128 } | |
| 129 delegate_->OnFilePathChanged(target_); | |
| 130 } else if (!file_exists && !last_modified_.is_null()) { | |
| 131 last_modified_ = base::Time(); | |
| 132 delegate_->OnFilePathChanged(target_); | |
| 133 } | |
| 134 | |
| 135 // The watch may have been cancelled by the callback. | |
| 136 if (handle_ != INVALID_HANDLE_VALUE) | |
| 137 watcher_.StartWatching(handle_, this); | |
| 138 } | |
| 139 | |
| 140 FilePathWatcherImpl::~FilePathWatcherImpl() { | |
| 141 if (handle_ != INVALID_HANDLE_VALUE) | |
| 142 DestroyWatch(); | |
| 143 } | |
| 144 | |
| 145 // static | |
| 146 bool FilePathWatcherImpl::SetupWatchHandle(const FilePath& dir, | |
| 147 HANDLE* handle) { | |
| 148 *handle = FindFirstChangeNotification( | |
| 149 dir.value().c_str(), | |
| 150 false, // Don't watch subtrees | |
| 151 FILE_NOTIFY_CHANGE_FILE_NAME | FILE_NOTIFY_CHANGE_SIZE | | |
| 152 FILE_NOTIFY_CHANGE_LAST_WRITE | FILE_NOTIFY_CHANGE_DIR_NAME | | |
| 153 FILE_NOTIFY_CHANGE_ATTRIBUTES | FILE_NOTIFY_CHANGE_SECURITY); | |
| 154 if (*handle != INVALID_HANDLE_VALUE) { | |
| 155 // Make sure the handle we got points to an existing directory. It seems | |
| 156 // that windows sometimes hands out watches to direectories that are | |
| 157 // about to go away, but doesn't sent notifications if that happens. | |
| 158 if (!file_util::DirectoryExists(dir)) { | |
| 159 FindCloseChangeNotification(*handle); | |
| 160 *handle = INVALID_HANDLE_VALUE; | |
| 161 } | |
| 162 return true; | |
| 163 } | |
| 164 | |
| 165 // If FindFirstChangeNotification failed because the target directory | |
| 166 // doesn't exist, access is denied (happens if the file is already gone but | |
| 167 // there are still handles open), or the target is not a directory, try the | |
| 168 // immediate parent directory instead. | |
| 169 DWORD error_code = GetLastError(); | |
| 170 if (error_code != ERROR_FILE_NOT_FOUND && | |
| 171 error_code != ERROR_PATH_NOT_FOUND && | |
| 172 error_code != ERROR_ACCESS_DENIED && | |
| 173 error_code != ERROR_SHARING_VIOLATION && | |
| 174 error_code != ERROR_DIRECTORY) { | |
| 175 PLOG(ERROR) << "FindFirstChangeNotification failed for " | |
| 176 << dir.value(); | |
| 177 return false; | |
| 178 } | |
| 179 | |
| 180 return true; | |
| 181 } | |
| 182 | |
| 183 bool FilePathWatcherImpl::UpdateWatch() { | |
| 184 if (handle_ != INVALID_HANDLE_VALUE) | |
| 185 DestroyWatch(); | |
| 186 | |
| 187 base::PlatformFileInfo file_info; | |
| 188 if (file_util::GetFileInfo(target_, &file_info)) { | |
| 189 last_modified_ = file_info.last_modified; | |
| 190 first_notification_ = base::Time::Now(); | |
| 191 } | |
| 192 | |
| 193 // Start at the target and walk up the directory chain until we succesfully | |
| 194 // create a watch handle in |handle_|. |child_dirs| keeps a stack of child | |
| 195 // directories stripped from target, in reverse order. | |
| 196 std::vector<FilePath> child_dirs; | |
| 197 FilePath watched_path(target_); | |
| 198 while (true) { | |
| 199 if (!SetupWatchHandle(watched_path, &handle_)) | |
| 200 return false; | |
| 201 | |
| 202 // Break if a valid handle is returned. Try the parent directory otherwise. | |
| 203 if (handle_ != INVALID_HANDLE_VALUE) | |
| 204 break; | |
| 205 | |
| 206 // Abort if we hit the root directory. | |
| 207 child_dirs.push_back(watched_path.BaseName()); | |
| 208 FilePath parent(watched_path.DirName()); | |
| 209 if (parent == watched_path) { | |
| 210 LOG(ERROR) << "Reached the root directory"; | |
| 211 return false; | |
| 212 } | |
| 213 watched_path = parent; | |
| 214 } | |
| 215 | |
| 216 // At this point, handle_ is valid. However, the bottom-up search that the | |
| 217 // above code performs races against directory creation. So try to walk back | |
| 218 // down and see whether any children appeared in the mean time. | |
| 219 while (!child_dirs.empty()) { | |
| 220 watched_path = watched_path.Append(child_dirs.back()); | |
| 221 child_dirs.pop_back(); | |
| 222 HANDLE temp_handle = INVALID_HANDLE_VALUE; | |
| 223 if (!SetupWatchHandle(watched_path, &temp_handle)) | |
| 224 return false; | |
| 225 if (temp_handle == INVALID_HANDLE_VALUE) | |
| 226 break; | |
| 227 FindCloseChangeNotification(handle_); | |
| 228 handle_ = temp_handle; | |
| 229 } | |
| 230 | |
| 231 return true; | |
| 232 } | |
| 233 | |
| 234 void FilePathWatcherImpl::DestroyWatch() { | |
| 235 watcher_.StopWatching(); | |
| 236 FindCloseChangeNotification(handle_); | |
| 237 handle_ = INVALID_HANDLE_VALUE; | |
| 238 } | |
| 239 | |
| 240 } // namespace | |
| 241 | |
| 242 FilePathWatcher::FilePathWatcher() { | |
| 243 impl_ = new FilePathWatcherImpl(); | |
| 244 } | |
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