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 "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
+// UI and FILE threads. See AsyncPolicyProvider::RefreshPolicies.
+void Nop() {}
+
+}  // namespace
+
+AsyncPolicyProvider::AsyncPolicyProvider(
+    const PolicyDefinitionList* policy_list,
+    AsyncPolicyLoader* loader)
+    : ConfigurationPolicyProvider(policy_list),
+      loader_(loader),
+      ALLOW_THIS_IN_INITIALIZER_LIST(weak_factory_(this)),
+      pending_refreshes_(0) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));

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

Rather use base::threading::NonThreadSafe? If you choose to do so, you should
also update the code below to call MessageLoop::current()->PostTask instead of
the BrowserThread variant.

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

Done. This also required passing the MessageLoop of the provider to the loader.

+  // The FILE thread isn't ready early during startup. Post a task to UI to
+  // resume initialization on FILE once the loops are spinning.
+  BrowserThread::PostTask(
+      BrowserThread::UI, FROM_HERE,
+      base::Bind(&AsyncPolicyProvider::InitWithLoopsReady,
+                 weak_factory_.GetWeakPtr()));
+  // Make an immediate synchronous load on startup.
+  OnLoaderReloaded(loader->InitialLoad());
+}
+
+AsyncPolicyProvider::~AsyncPolicyProvider() {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  // 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_| on UI, which has a WeakPtr to |this|.
+  BrowserThread::DeleteSoon(BrowserThread::FILE, FROM_HERE, loader_);
+}
+
+void AsyncPolicyProvider::RefreshPolicies() {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  pending_refreshes_++;
+  // 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 test has modified the policy settings and

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

Seems like this doesn't only apply to tests.

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

s/test/caller

+  // 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() to UI. Therefore a task is posted to
+  // FILE before posting the next Reload, to prevent a potential concurrent
+  // Reload() from triggered a notification too early.

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

s/triggered/triggering/

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

Done.

+  BrowserThread::PostTaskAndReply(
+      BrowserThread::FILE, FROM_HERE,
+      base::Bind(Nop),
+      base::Bind(&AsyncPolicyProvider::PostRefreshingReload,
+                 weak_factory_.GetWeakPtr()));
+}
+
+void AsyncPolicyProvider::InitWithLoopsReady() {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  BrowserThread::PostTask(
+      BrowserThread::FILE, FROM_HERE,
+      base::Bind(&AsyncPolicyLoader::Init,
+                 base::Unretained(loader_),
+                 base::Bind(&AsyncPolicyProvider::OnLoaderReloaded,
+                            weak_factory_.GetWeakPtr())));
+}
+
+void AsyncPolicyProvider::PostRefreshingReload() {

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

The name of this function is not very descriptive, and in fact, I couldn't tell
from the name what it's supposed to do. I suggest "ReloadAfterRefreshSync".

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

Done.

+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  DCHECK(pending_refreshes_ > 0);
+  pending_refreshes_--;

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

Ah, counters. In this case, it's probably not an issue, but if I were to write
this code, I would use a separate weak pointer factory (or CancellableCallback)
to just clear all earlier posted refreshes in subsequent RefreshPolicies()
invocations.

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

Redone with a CancellableCallback as suggested offline.

+  if (pending_refreshes_ == 0) {
+    BrowserThread::PostTask(
+        BrowserThread::FILE, FROM_HERE,
+        base::Bind(&AsyncPolicyLoader::Reload,
+                   base::Unretained(loader_),
+                   true  /* force */));
+  }
+}
+
+void AsyncPolicyProvider::OnLoaderReloaded(scoped_ptr<PolicyBundle> bundle) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  if (pending_refreshes_ == 0)
+    UpdatePolicy(bundle.Pass());
+}
+
+}  // namespace policy