Add the AsyncPolicyProvider and AsyncPolicyLoader

chrome/browser/policy/async_policy_provider.cc

+// 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.
+
+#include "chrome/browser/policy/async_policy_provider.h"
+
+#include "base/bind.h"
+#include "base/bind_helpers.h"
+#include "base/message_loop.h"
+#include "base/message_loop_proxy.h"
+#include "chrome/browser/policy/async_policy_loader.h"
+#include "chrome/browser/policy/policy_bundle.h"
+#include "content/public/browser/browser_thread.h"
+
+using content::BrowserThread;
+
+namespace policy {
+
+namespace {
+
+// Helper for a PostTaskAndReply used as a synchronization point between the
+// main thread and FILE thread. See AsyncPolicyProvider::RefreshPolicies.
+void Nop() {}
+
+}  // namespace
+
+AsyncPolicyProvider::AsyncPolicyProvider(
+    const PolicyDefinitionList* policy_list,
+    scoped_ptr<AsyncPolicyLoader> loader)
+    : ConfigurationPolicyProvider(policy_list),
+      loader_(loader.release()),
+      ALLOW_THIS_IN_INITIALIZER_LIST(weak_factory_(this)) {
+  // The FILE thread isn't ready early during startup. Post a task to the
+  // current loop to resume initialization on FILE once the loops are spinning.
+  MessageLoop::current()->PostTask(
+      FROM_HERE,
+      base::Bind(&AsyncPolicyProvider::InitWithLoopsReady,
+                 weak_factory_.GetWeakPtr()));
+  // Make an immediate synchronous load on startup.
+  OnLoaderReloaded(loader_->InitialLoad());
+}
+
+AsyncPolicyProvider::~AsyncPolicyProvider() {
+  DCHECK(CalledOnValidThread());
+
+  // Note on the lifetime of |loader_|:
+  // The |loader_| lives on the FILE thread, and is deleted from here. This
+  // means that posting tasks on the |loader_| to FILE from the
+  // AsyncPolicyProvider is always safe, since a potential DeleteSoon() is only
+  // posted from here. The |loader_| posts back to the AsyncPolicyProvider
+  // through the |update_callback_|, which has a WeakPtr to |this|.
+  BrowserThread::DeleteSoon(BrowserThread::FILE, FROM_HERE, loader_);
+}
+
+void AsyncPolicyProvider::RefreshPolicies() {
+  DCHECK(CalledOnValidThread());
+
+  // Subtle: RefreshPolicies() has a contract that requires the next policy
+  // update notification (triggered from UpdatePolicy()) to reflect any changes
+  // made before this call. So if a caller has modified the policy settings and
+  // invoked RefreshPolicies(), then by the next notification these policies
+  // should already be provided.
+  // However, it's also possible that an asynchronous Reload() is in progress
+  // and just posted OnLoaderReloaded(). Therefore a task is posted to the
+  // FILE thread before posting the next Reload, to prevent a potential
+  // concurrent Reload() from triggering a notification too early. If another
+  // refresh task has been posted, it is invalidated now.
+  refresh_callback_.Reset(
+      base::Bind(&AsyncPolicyProvider::ReloadAfterRefreshSync,
+                 base::Unretained(this)));
+  BrowserThread::PostTaskAndReply(
+      BrowserThread::FILE, FROM_HERE,
+      base::Bind(Nop),
+      refresh_callback_.callback());
+}
+
+void AsyncPolicyProvider::InitWithLoopsReady() {
+  DCHECK(CalledOnValidThread());
+  BrowserThread::PostTask(
+      BrowserThread::FILE, FROM_HERE,
+      base::Bind(&AsyncPolicyLoader::Init,
+                 base::Unretained(loader_),
+                 base::MessageLoopProxy::current(),
+                 base::Bind(&AsyncPolicyProvider::OnLoaderReloaded,
+                            weak_factory_.GetWeakPtr())));
+}
+
+void AsyncPolicyProvider::ReloadAfterRefreshSync() {
+  DCHECK(CalledOnValidThread());
+  // This task can only enter if it was posted from RefreshPolicies(), and it
+  // hasn't been cancelled meanwhile by another call to RefreshPolicies().
+  DCHECK(!refresh_callback_.IsCancelled());
+  // There can't be another refresh callback pending now, since its creation
+  // in RefreshPolicies() would have cancelled the current execution. So it's
+  // safe to cancel the |refresh_callback_| now, so that OnLoaderReloaded()
+  // sees that there is no refresh pending.
+  refresh_callback_.Cancel();
+
+  BrowserThread::PostTask(
+      BrowserThread::FILE, FROM_HERE,
+      base::Bind(&AsyncPolicyLoader::Reload,
+                 base::Unretained(loader_),
+                 true  /* force */));
+}
+
+void AsyncPolicyProvider::OnLoaderReloaded(scoped_ptr<PolicyBundle> bundle) {
+  DCHECK(CalledOnValidThread());
+  if (refresh_callback_.IsCancelled())
+    UpdatePolicy(bundle.Pass());
+}
+
+}  // namespace policy