Add the AsyncPolicyProvider and AsyncPolicyLoader

chrome/browser/policy/async_policy_loader.h

+// Copyright (c) 2012 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 CHROME_BROWSER_POLICY_ASYNC_POLICY_LOADER_H_
+#define CHROME_BROWSER_POLICY_ASYNC_POLICY_LOADER_H_
+#pragma once
+
+#include "base/callback.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/memory/scoped_vector.h"
+#include "base/memory/weak_ptr.h"
+#include "base/time.h"
+
+class FilePath;
+
+namespace base {
+namespace files {
+class FilePathWatcher;
+}  // namespace files
+}  // namespace base
+
+namespace policy {
+
+class PolicyBundle;
+
+// Base implementation for platform-specific policy loaders. Together with the
+// AsyncPolicyProvider, this base implementation takes care of the initial load,
+// periodic reloads, watching file changes, refreshing policies and object
+// lifetime.
+//
+// All methods are invoked on FILE, including the destructor. The only
+// exceptions are the constructor (which may be called on any thread), and the
+// initial Load() which is called on UI. LastModificationTime() is also invoked
+// once on UI at startup.
+class AsyncPolicyLoader {
+ public:
+  AsyncPolicyLoader();
+  virtual ~AsyncPolicyLoader();
+
+  // Returns the currently configured policies. Load() is always invoked on
+  // FILE, except for the initial Load() at startup which is invoked from UI.

[Mattias Nissler (ping if slow), 2012/06/04 08:48:26]

say FILE _thread_, otherwise this won't make any sense to people not intimately
experienced with the project. Same from UI (also elsewhere in this file).

[Joao da Silva, 2012/06/04 14:05:06]

Done.

+  virtual scoped_ptr<PolicyBundle> Load() = 0;
+
+  // Allows implementations to finalize their initialization on the FILE
+  // thread (e.g. setup file watchers with WatchPath()).
+  virtual void InitOnFile() = 0;
+
+  // Implementations should return the time of the last modification detected,
+  // or base::Time() if it doesn't apply, which is the default.
+  virtual base::Time LastModificationTime();
+
+  // Implementations should invoke Reload() when a change is detected. This
+  // must be invoked from FILE and will trigger a Load(), and pass the
+  // returned bundle to the provider.
+  // The load is immediate when |force| is true. Otherwise, the loader
+  // reschedules the reload until the LastModificationTime() is a couple of
+  // seconds in the past.

[Mattias Nissler (ping if slow), 2012/06/04 08:48:26]

explain why.

[Joao da Silva, 2012/06/04 14:05:06]

Done.

+  //
+  // A reload is posted periodically, and whenever changes are detected to
+  // paths passed to WatchPath().
+  void Reload(bool force);
+
+  // Starts watching |path| and posts Reload() whenever a change is detected.
+  // Must be invoked on FILE.
+  void WatchPath(const FilePath& path);

[Mattias Nissler (ping if slow), 2012/06/04 08:48:26]

seems like this should be protected.

[Joao da Silva, 2012/06/04 14:05:06]

Obsolete; this has been removed, as suggested elsewhere.

+
+ private:
+  // Allow AsyncPolicyProvider to call Init().
+  friend class AsyncPolicyProvider;
+
+  typedef base::Callback<void(scoped_ptr<PolicyBundle>)> UpdateCallback;
+
+  // Used by the AsyncPolicyProvider to do the initial Load(). The first load
+  // is also used to initialize |last_modification_time_|.
+  scoped_ptr<PolicyBundle> InitialLoad();
+
+  // Used by the AsyncPolicyProvider to install the |update_callback_|.
+  // Invoked on FILE.
+  void Init(const UpdateCallback& update_callback);
+
+  // Cancels any pending periodic reload and posts one |delay| time units from
+  // now.
+  void ScheduleNextReload(base::TimeDelta delay);
+
+  // Checks if the underlying files haven't changed recently, by checking the
+  // LastModificationTime(). |delay| is updated with a suggested time to wait
+  // before retrying when this returns false.
+  bool IsSafeToReload(const base::Time& now, base::TimeDelta* delay);
+
+  // Callback for updates, passed in Init().
+  UpdateCallback update_callback_;
+
+  // |reload_weak_factory_| is used to get WeakPtrs for the periodic reload
+  // tasks, and |watchers_weak_factory_| to get WeakPtrs for the update callback
+  // passed to the |watchers_|. They're separate because |reload_weak_factory_|
+  // is invalidated whenever a new reload is scheduled, while

[Mattias Nissler (ping if slow), 2012/06/04 08:48:26]

use base/timer.h instead?

[Joao da Silva, 2012/06/04 14:05:06]

The weak factory for the watchers is now gone. I tried using a Timer for the
periodic refresh task, but ScheduleNextReload() is also used to post reloads
"soon" after the settle period; resetting the Timer to trigger once with a
different delay was a bit clunky, so I've left the weak_factory for reloads
only.

+  // |watchers_weak_factory_| is valid until destruction of |this| object.
+  base::WeakPtrFactory<AsyncPolicyLoader> reload_weak_factory_;
+  base::WeakPtrFactory<AsyncPolicyLoader> watchers_weak_factory_;
+
+  // Records last known modification timestamp.
+  base::Time last_modification_time_;
+
+  // The wall clock time at which the last modification timestamp was
+  // recorded.  It's better to not assume the file notification time and the
+  // wall clock times come from the same source, just in case there is some
+  // non-local filesystem involved.
+  base::Time last_modification_clock_;
+
+  // List of watchers, one per call to WatchPath.
+  ScopedVector<base::files::FilePathWatcher> watchers_;
+
+  DISALLOW_COPY_AND_ASSIGN(AsyncPolicyLoader);
+};
+
+}  // namespace policy
+
+#endif  // CHROME_BROWSER_POLICY_ASYNC_POLICY_LOADER_H_