Use FSEvents for recursive file watch on Mac

base/files/file_path_watcher_fsevents.h

+// Copyright 2014 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.
+
+#ifndef BASE_FILES_FILE_PATH_WATCHER_FSEVENTS_H_
+#define BASE_FILES_FILE_PATH_WATCHER_FSEVENTS_H_
+
+#include <CoreServices/CoreServices.h>
+
+#include <vector>
+
+#include "base/files/file_path.h"
+#include "base/files/file_path_watcher.h"
+
+namespace base {
+
+// There are trade-offs between the FSEvents implementation and a kqueue
+// implementation. The biggest issues are that FSEvents on 10.6 sometimes drops
+// events and kqueue does not trigger for modifications to a file in a watched
+// directory.

[Mattias Nissler (ping if slow), 2014/05/26 07:39:37]

Would be good to add a sentence explaining which strategy we use for deciding
whether we want to use kqueue and/or fsevents?

[vandebo (ex-Chrome), 2014/05/28 00:26:55]

Done.

+class FilePathWatcherFSEvents : public FilePathWatcher::PlatformDelegate {
+ public:
+  FilePathWatcherFSEvents();
+
+  // Called from the FSEvents callback whenever there is a change to the paths

[Mattias Nissler (ping if slow), 2014/05/26 07:39:37]

Missing period.

[vandebo (ex-Chrome), 2014/05/28 00:26:55]

Done.

+  void OnFilePathChanged(const std::vector<FilePath>& paths);

[Mattias Nissler (ping if slow), 2014/05/26 07:39:37]

nit: Name is inconsistent, should probably be OnFilePathsChanged (note the
plural)

[vandebo (ex-Chrome), 2014/05/28 00:26:55]

Done.

+
+  // (Re-)Initialize the event stream to start reporting events from
+  // |start_event|.
+  void UpdateEventStream(FSEventStreamEventId start_event);
+
+  // FilePathWatcher::PlatformDelegate overrides.
+  virtual bool Watch(const FilePath& path,
+                     bool recursive,
+                     const FilePathWatcher::Callback& callback) OVERRIDE;
+  virtual void Cancel() OVERRIDE;
+
+ private:
+  virtual ~FilePathWatcherFSEvents();
+
+  // Destroy the event stream.
+  void DestroyEventStream();
+
+  // Start watchign the FSEventStream.

[Mattias Nissler (ping if slow), 2014/05/26 07:39:37]

*watching

[vandebo (ex-Chrome), 2014/05/28 00:26:55]

Done.

+  void StartEventStream(const base::FilePath& target,
+                        FSEventStreamEventId start_event);
+
+  // Cleans up and stops the event stream.
+  virtual void CancelOnMessageLoopThread() OVERRIDE;
+
+  // Callback to notify upon changes.
+  FilePathWatcher::Callback callback_;
+
+  // Target path to watch (passed to callback).
+  FilePath target_;
+
+  // Backend stream we receive event callbacks from (strong reference).
+  FSEventStreamRef fsevent_stream_;
+
+  DISALLOW_COPY_AND_ASSIGN(FilePathWatcherFSEvents);
+};
+
+}  // namespace
+
+#endif  // BASE_FILES_FILE_PATH_WATCHER_FSEVENTS_H_