Refactor FileBasedPolicyProvider, introduce AsynchronousPolicyProvider.

chrome/browser/policy/asynchronous_policy_provider.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.
+
+#ifndef CHROME_BROWSER_POLICY_ASYNCHRONOUS_POLICY_PROVIDER_H_
+#define CHROME_BROWSER_POLICY_ASYNCHRONOUS_POLICY_PROVIDER_H_
+#pragma once
+
+#include "base/ref_counted.h"
+#include "base/time.h"
+#include "base/weak_ptr.h"
+#include "chrome/browser/policy/configuration_policy_provider.h"
+
+class CancelableTask;
+class MessageLoop;
+
+namespace policy {
+
+class AsynchronousPolicyLoader;
+
+// Policy provider that loads policy asynchronously. Providers subclass should

[battre (please use the other), 2010/12/02 17:40:25]

Nit: singular/plural in "Providers subclass"?

[danno, 2010/12/03 17:05:38]

Done.

+// subclass from this class if loading the policy requires disk access or must
+// for some other reason be performed on the file thread. The actual logic for
+// loading policy is handled by a delegate passed at construction time.
+class AsynchronousPolicyProvider
+    : public ConfigurationPolicyProvider,
+      public base::SupportsWeakPtr<AsynchronousPolicyProvider> {
+ public:
+  class PolicyChangeObserver;
+
+  // Must be implemented by subclasses of the asynchronous policy provider to
+  // provide the implementation details of when and how policy is loaded.
+  class Delegate {
+   public:
+    Delegate() {}
+    virtual ~Delegate() {}
+
+    // Called on the ui thread to provide the back channel with which delegates
+    // notify the provider that policy has changed and should be reloaded.
+    // The delegate assumes ownership of |observer|.
+    virtual void Init(PolicyChangeObserver* observer) = 0;
+
+    // Called on the ui thread by the provider to indicate that the delegate
+    // should stop providing policy. The delegate must delete the observer that
+    // it was passed during Init at the very latest during this call.

[battre (please use the other), 2010/12/02 17:40:25]

Is it guaranteed that Stop() is called, i.e. the observer gets deleted?

[danno, 2010/12/03 17:05:38]

Done.

+    virtual void Stop() = 0;
+
+    // Load policies, returning a dictionary of the policy to value
+    // mappings. Will always be called on the file thread.
+    virtual DictionaryValue* Load() = 0;
+
+    // Checks whether policy information is safe to read. If not, returns
+    // false and the delay until it is considered safe to reload in |delay|.

[battre (please use the other), 2010/12/02 17:40:25]

Nit: "then" "delays"

[danno, 2010/12/03 17:05:38]

Done.

+    // Will always be called on the file thread.
+    virtual bool IsSafeToReloadPolicy(const base::Time& now,
+                                      base::TimeDelta* delay) = 0;
+
+   private:
+    DISALLOW_COPY_AND_ASSIGN(Delegate);
+  };
+
+  // Assumes ownership of |delegate|.
+  AsynchronousPolicyProvider(
+      const PolicyDefinitionList* policy_list,
+      Delegate* delegate);
+  virtual ~AsynchronousPolicyProvider();
+
+  // ConfigurationPolicyProvider implementation.
+  virtual bool Provide(ConfigurationPolicyStoreInterface* store);
+
+ private:
+  // The loader object used internally.
+  scoped_refptr<AsynchronousPolicyLoader> loader_;
+
+  // The policy provider delegate.
+  Delegate* delegate_;  // weak, owned by loader
+
+  DISALLOW_COPY_AND_ASSIGN(AsynchronousPolicyProvider);
+};
+
+// Observer interface implemented by the asynchronous policy provider and passed
+// to policy provider delegates as a back channel to indicate when policy should
+// be reloaded.
+class AsynchronousPolicyProvider::PolicyChangeObserver {
+ public:
+  virtual ~PolicyChangeObserver() {}
+
+  virtual void OnPolicyChange() = 0;
+
+ protected:
+  PolicyChangeObserver() {}
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(PolicyChangeObserver);
+};
+
+}  // namespace policy
+
+#endif  // CHROME_BROWSER_POLICY_ASYNCHRONOUS_POLICY_PROVIDER_H_