Battery Status API: browser-side implementation.

content/browser/battery_status/battery_status_service.cc

+// Copyright 2014 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 "content/browser/battery_status/battery_status_service.h"
+
+#include "base/bind.h"
+#include "content/browser/battery_status/battery_status_manager.h"
+#include "content/public/browser/browser_thread.h"
+
+namespace content {
+
+static void AddCallbackIfNecessary(
+    std::vector<BatteryStatusUpdateCallback>& callbacks,
+    const BatteryStatusUpdateCallback& callback) {
+  for (size_t i = 0; i < callbacks.size(); ++i) {
+    if (callbacks[i].Equals(callback))
+      return;
+  }
+  callbacks.push_back(callback);
+}
+
+static void RemoveCallbackIfNecessary(
+    std::vector<BatteryStatusUpdateCallback>& callbacks,
+    const BatteryStatusUpdateCallback& callback) {
+  for (size_t i = 0; i < callbacks.size(); ++i) {
+    if (callbacks[i].Equals(callback)) {
+      callbacks[i] = callbacks.back();
+      callbacks.pop_back();
+      return;
+    }
+  }
+}
+
+BatteryStatusService::BatteryStatusService()
+    : status_updated_(false),
+      is_shutdown_(false) {
+  update_callback_ = base::Bind(&BatteryStatusService::UpdateBatteryStatus,
+                                base::Unretained(this));
+}
+
+BatteryStatusService::~BatteryStatusService() {
+}
+
+BatteryStatusService* BatteryStatusService::GetInstance() {
+  return Singleton<BatteryStatusService,
+                   LeakySingletonTraits<BatteryStatusService> >::get();
+}
+
+void BatteryStatusService::AddCallback(
+    const BatteryStatusUpdateCallback& callback) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
+  DCHECK(!is_shutdown_);
+
+  if (!battery_fetcher_)
+    battery_fetcher_.reset(new BatteryStatusManager(update_callback_));
+
+  if (callbacks_.empty())
+    battery_fetcher_->StartListeningBatteryChange();
+
+  if (status_updated_) {
+    // Send recent status to the new callback if already available.
+    callback.Run(status_);
+  }
+
+  AddCallbackIfNecessary(callbacks_, callback);

[jochen (gone - plz use gerrit), 2014/05/19 13:14:22]

can this actually happen that the same callback is added muliple times?

[timvolodine, 2014/05/22 10:02:33]

actually no, the message filter keeps track of whether it is started, so I've
probably over-engineered this a bit. This is now solved by using CallbackList.

+}
+
+void BatteryStatusService::RemoveCallback(
+    const BatteryStatusUpdateCallback& callback) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
+  DCHECK(!is_shutdown_);
+
+  RemoveCallbackIfNecessary(callbacks_, callback);
+
+  if (callbacks_.empty()) {
+    battery_fetcher_->StopListeningBatteryChange();
+    status_updated_ = false;
+  }
+}
+
+const BatteryStatusUpdateCallback&
+BatteryStatusService::update_callback() const {
+  return update_callback_;
+}
+
+void BatteryStatusService::UpdateBatteryStatus(
+    const blink::WebBatteryStatus& status) {
+  DCHECK(!is_shutdown_);
+  BrowserThread::PostTask(BrowserThread::IO,

[Michael van Ouwerkerk, 2014/05/19 11:19:22]

I think you can turn BatteryStatusMessageFilter into a WebContentsObserver, so
that all the messages are handled on the UI thread. You can omit all the thread
checking and hopping code, and the comments, that way. Probably rename it to
BatteryStatusDispatcher then.

See this patch for the kind of unnecessary complexity you might otherwise end up
with: https://codereview.chromium.org/273523007/

[timvolodine, 2014/05/22 10:02:33]

The idea is to keep non-UI things away from the UI thread. Battery is clearly IO
so should preferably be handled on IO thread as much as possible. In the current
approach the UpdateBatteryStatus method can be called from any thread also
allowing simpler implementations for other platforms if they happen to use yet
another thread for battery fetching.

+                          FROM_HERE,
+                          base::Bind(&BatteryStatusService::NotifyConsumers,
+                                     base::Unretained(this), status));
+}
+
+void BatteryStatusService::NotifyConsumers(
+    const blink::WebBatteryStatus& status) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
+
+  if (callbacks_.empty())
+    return;
+
+  status_ = status;
+  status_updated_ = true;
+  std::vector<BatteryStatusUpdateCallback>::const_iterator it =
+      callbacks_.begin();
+  for (; it != callbacks_.end(); ++it)
+    (*it).Run(status_);
+}
+
+void BatteryStatusService::Shutdown() {
+  battery_fetcher_.reset();
+  is_shutdown_ = true;
+}
+
+void BatteryStatusService::SetBatteryManagerForTests(
+    BatteryStatusManagerInterface* test_battery_manager) {
+  battery_fetcher_.reset(test_battery_manager);
+  blink::WebBatteryStatus status;
+  status_ = status;
+  status_updated_ = false;
+  callbacks_.clear();
+}
+
+}  // namespace content