Getting service process on Mac to handle having things moved/changed underneath it.

base/file_path_component_watcher.h

+// Copyright (c) 2010 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.
+
+// This module provides a way to monitor a filepath for changes in the path.
+
+#ifndef BASE_FILE_PATH_COMPONENT_WATCHER_H_
+#define BASE_FILE_PATH_COMPONENT_WATCHER_H_
+#pragma once
+
+#include "base/basictypes.h"
+#include "base/file_path.h"
+#include "base/ref_counted.h"
+
+namespace base {
+// This class lets you register interest in changes on a FilePath.
+// The delegate will get called whenever any components of a FilePath are
+// changed (moved, deleted, attributes changed). This is different from
+// FilePathWatcher, in that FilePathWatcher watches a single file, and it's
+// parent directory for changes, whereas this watches each component in a file's
+// path for changes.
+// A watcher will only register a single notification.
+class FilePathComponentWatcher {
+ public:
+  // Declares the callback client code implements to receive notifications. Note
+  // that implementations of this interface should not keep a reference to the
+  // corresponding FileWatcher object to prevent a reference cycle.
+  class Delegate : public base::RefCountedThreadSafe<Delegate> {
+   public:
+    virtual ~Delegate() {}
+    virtual void OnFilePathComponentsChanged(const FilePath& old_path,
+                                             const FilePath& new_path) = 0;
+    // Called when platform specific code detected an error. The watcher will
+    // not call OnFilePathChanged for future changes.
+    virtual void OnError() {}
+  };
+
+  FilePathComponentWatcher();
+  ~FilePathComponentWatcher();
+
+  // Register interest in any changes on |path|. OnPathChanged will be called
+  // back for each change. Returns true on success.
+  bool Watch(const FilePath& path, Delegate* delegate) WARN_UNUSED_RESULT;
+
+  // Used internally to encapsulate different members on different platforms.
+  class PlatformDelegate
+      : public base::RefCountedThreadSafe<PlatformDelegate> {
+   public:
+    virtual ~PlatformDelegate() {}
+
+    // Start watching for the given |path| and notify |delegate| about changes.
+    virtual bool Watch(const FilePath& path, Delegate* delegate)
+        WARN_UNUSED_RESULT = 0;
+
+    // Stop watching. This is called from FilePathComponentWatcher's dtor 
+    // in order to allow it to shut down properly while the object is still 
+    // alive.
+    virtual void Cancel() {}
+  };
+
+ private:
+  scoped_refptr<PlatformDelegate> impl_;
+
+  DISALLOW_COPY_AND_ASSIGN(FilePathComponentWatcher);
+};
+
+}  // namespace
+
+#endif  // BASE_FILE_PATH_COMPONENT_WATCHER_H_