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/weak_ptr.h"
+#include "base/message_loop_proxy.h"
+#include "base/time.h"
+
+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 the FILE thread, including the destructor.
+// The only exceptions are the constructor (which may be called on any thread),
+// and the initial Load() which is called on the thread that owns the provider.
+// LastModificationTime() is also invoked once on that thread at startup.
+class AsyncPolicyLoader {
+ public:
+  AsyncPolicyLoader();
+  virtual ~AsyncPolicyLoader();
+
+  // Returns the currently configured policies. Load() is always invoked on
+  // the FILE thread, except for the initial Load() at startup which is invoked
+  // from the thread that owns the provider.
+  virtual scoped_ptr<PolicyBundle> Load() = 0;
+
+  // Allows implementations to finalize their initialization on the FILE
+  // thread (e.g. setup file watchers).
+  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 the FILE thread 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. This mitigates the problem of reading files that are
+  // currently being written to, and whose contents are incomplete.
+  // A reload is posted periodically, if it hasn't been triggered recently. This
+  // makes sure the policies are reloaded if the update events aren't triggered.
+  void Reload(bool force);
+
+ 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_|, which
+  // should be posted to the |provider_loop_| on updates.
+  // Invoked on the FILE thread.
+  void Init(scoped_refptr<base::MessageLoopProxy> provider_loop,

[Mattias Nissler (ping if slow), 2012/06/04 15:25:39]

Do we really need the loop? It seems that AsyncPolicyProvider could supply a
callback that can handle running on FILE and does the thread switching behind
the scenes. That way, all thread switching would be in AsyncPolicyProvider,
which would be more consistent and tidy.

[Joao da Silva, 2012/06/04 17:28:12]

Done.

+            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(). It is posted to the
+  // |provider_loop_| on updates..

[Mattias Nissler (ping if slow), 2012/06/04 15:25:39]

Excess period

[Joao da Silva, 2012/06/04 17:28:12]

Done.

+  UpdateCallback update_callback_;
+  scoped_refptr<base::MessageLoopProxy> provider_loop_;
+
+  // Used to get WeakPtrs for the periodic reload task.
+  base::WeakPtrFactory<AsyncPolicyLoader> 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_;
+
+  DISALLOW_COPY_AND_ASSIGN(AsyncPolicyLoader);
+};
+
+}  // namespace policy
+
+#endif  // CHROME_BROWSER_POLICY_ASYNC_POLICY_LOADER_H_