Media Galleries API Picasa: Add file watch to invalidate database data on disk write.

chrome/browser/media_galleries/fileapi/file_path_watcher_util.cc

+// Copyright 2013 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 "chrome/browser/media_galleries/fileapi/file_path_watcher_util.h"
+
+#include "base/bind.h"
+#include "base/callback.h"
+#include "base/location.h"
+#include "base/logging.h"
+#include "chrome/browser/media_galleries/fileapi/media_file_system_backend.h"
+#include "content/public/browser/browser_thread.h"
+
+namespace chrome {
+
+namespace {
+
+// Bounces |path| and |error| to |callback| from the FILE thread to the media
+// task runner.
+void OnFilePathChangedOnFileThread(
+    const base::FilePathWatcher::Callback& callback,
+    const base::FilePath& path,
+    bool error) {
+  DCHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::FILE));
+  MediaFileSystemBackend::MediaTaskRunner()->PostTask(
+      FROM_HERE, base::Bind(callback, path, error));
+}
+
+// The watch has to be started on the FILE thread, and the callback called by
+// the FilePathWatcher also needs to run on the FILE thread.
+void StartFilePathWatchOnFileThread(
+    const base::FilePath& path,
+    const FileWatchStartedCallback& watch_started_callback,
+    const base::FilePathWatcher::Callback& path_changed_callback) {
+  DCHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::FILE));
+  // The watcher is created on the FILE thread because it is very difficult
+  // to safely pass an already-created file watcher to a different thread.
+  scoped_ptr<base::FilePathWatcher> watcher(new base::FilePathWatcher);
+  bool success = watcher->Watch(
+      path,
+      false /* recursive */,
+      base::Bind(&OnFilePathChangedOnFileThread, path_changed_callback));
+  if (!success)
+    LOG(ERROR) << "Adding watch for " << path.value() << " failed";
+  MediaFileSystemBackend::MediaTaskRunner()->PostTask(
+      FROM_HERE, base::Bind(watch_started_callback, base::Passed(&watcher)));
+}
+
+}  // namespace
+
+void StartFilePathWatchOnMediaTaskRunner(
+    const base::FilePath& path,
+    const FileWatchStartedCallback& watch_started_callback,
+    const base::FilePathWatcher::Callback& path_changed_callback) {
+  DCHECK(MediaFileSystemBackend::CurrentlyOnMediaTaskRunnerThread());
+  content::BrowserThread::PostTask(content::BrowserThread::FILE,
+                                   FROM_HERE,
+                                   base::Bind(&StartFilePathWatchOnFileThread,
+                                              path,
+                                              watch_started_callback,
+                                              path_changed_callback));
+}
+
+}  // namespace chrome