Add a FileWatcher to base/.

base/file_watcher_win.cc

+// Copyright (c) 2009 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "base/file_watcher.h"
+
+#include "base/file_path.h"
+#include "base/file_util.h"
+#include "base/logging.h"
+#include "base/object_watcher.h"
+#include "base/ref_counted.h"
+#include "base/time.h"
+
+namespace {
+
+class FileWatcherImpl : public FileWatcher::PlatformDelegate,
+                        public base::ObjectWatcher::Delegate {
+ public:
+  FileWatcherImpl() : delegate_(NULL), handle_(INVALID_HANDLE_VALUE) {}
+
+  virtual bool Watch(const FilePath& path, FileWatcher::Delegate* delegate,
+                     MessageLoop* backend_loop);
+
+  // Callback from MessageLoopForIO.
+  virtual void OnObjectSignaled(HANDLE object);
+
+ private:
+  virtual ~FileWatcherImpl();
+
+  // Delegate to notify upon changes.
+  FileWatcher::Delegate* delegate_;
+
+  // Path we're watching (passed to delegate).
+  FilePath path_;
+
+  // Handle for FindFirstChangeNotification.
+  HANDLE handle_;
+
+  // ObjectWatcher to watch handle_ for events.
+  base::ObjectWatcher watcher_;
+
+  // Keep track of the last modified time of the file.  We use nulltime
+  // to represent the file not existing.
+  base::Time last_modified_;
+
+  DISALLOW_COPY_AND_ASSIGN(FileWatcherImpl);
+};
+
+FileWatcherImpl::~FileWatcherImpl() {
+  if (handle_ != INVALID_HANDLE_VALUE) {
+    watcher_.StopWatching();
+    FindCloseChangeNotification(handle_);
+  }
+}
+
+bool FileWatcherImpl::Watch(const FilePath& path,
+                            FileWatcher::Delegate* delegate,
+                            MessageLoop* backend_loop) {
+  DCHECK(path_.value().empty());  // Can only watch one path.
+  file_util::FileInfo file_info;
+  if (file_util::GetFileInfo(path, &file_info))
+    last_modified_ = file_info.last_modified;
+
+  // FindFirstChangeNotification watches directories, so use the parent path.
+  handle_ = FindFirstChangeNotification(
+      path.DirName().value().c_str(),
+      false,  // Don't watch subtrees
+      FILE_NOTIFY_CHANGE_FILE_NAME | FILE_NOTIFY_CHANGE_SIZE |
+      FILE_NOTIFY_CHANGE_LAST_WRITE | FILE_NOTIFY_CHANGE_DIR_NAME);
+  if (handle_ == INVALID_HANDLE_VALUE)
+    return false;
+
+  delegate_ = delegate;
+  path_ = path;
+  watcher_.StartWatching(handle_, this);
+
+  return true;
+}
+
+void FileWatcherImpl::OnObjectSignaled(HANDLE object) {
+  DCHECK(object == handle_);
+  // Make sure we stay alive through the body of this function.
+  scoped_refptr<FileWatcherImpl> keep_alive(this);
+
+  file_util::FileInfo file_info;
+  bool file_exists = file_util::GetFileInfo(path_, &file_info);
+  if (file_exists && (last_modified_.is_null() ||
+      last_modified_ != file_info.last_modified)) {
+    last_modified_ = file_info.last_modified;
+    delegate_->OnFileChanged(path_);
+  } else if (file_exists && (base::Time::Now() - last_modified_ <
+             base::TimeDelta::FromSeconds(2))) {
+    // Since we only have a resolution of 1s, if we get a callback within
+    // 2s of the file having changed, go ahead and notify our observer.  This
+    // might be from a different file change, but it's better to notify too
+    // much rather than miss a notification.
+    delegate_->OnFileChanged(path_);
+  } else if (!file_exists && !last_modified_.is_null()) {
+    last_modified_ = base::Time();
+    delegate_->OnFileChanged(path_);
+  }
+
+  // Register for more notifications on file change.
+  BOOL ok = FindNextChangeNotification(object);
+  DCHECK(ok);
+  watcher_.StartWatching(object, this);
+}
+
+}  // namespace
+
+FileWatcher::FileWatcher() {
+  impl_ = new FileWatcherImpl();
+}