Implement device_orientation::Provider.

chrome/browser/device_orientation/provider_impl.cc

+// 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.
+
+#include <cmath>
+#include <set>
+#include <vector>
+
+#include "base/logging.h"
+#include "base/task.h"
+#include "chrome/browser/chrome_thread.h"
+#include "chrome/browser/device_orientation/orientation.h"
+#include "chrome/browser/device_orientation/provider_impl.h"
+
+namespace device_orientation {
+
+ProviderImpl::ProviderImpl(MessageLoop* message_loop,
+                           const DataFetcherFactory factories[])
+    : creator_loop_(message_loop),
+      ALLOW_THIS_IN_INITIALIZER_LIST(do_poll_method_factory_(this)) {
+  for (const DataFetcherFactory* fp = factories; *fp; ++fp)
+    factories_.push_back(*fp);
+}
+
+ProviderImpl::~ProviderImpl() {
+}
+
+void ProviderImpl::AddObserver(Observer* observer) {
+  DCHECK(MessageLoop::current() == creator_loop_);
+
+  observers_.insert(observer);
+  if (observers_.size() == 1)
+    Start();
+  else
+    observer->OnOrientationUpdate(last_notification_);
+}
+
+void ProviderImpl::RemoveObserver(Observer* observer) {
+  DCHECK(MessageLoop::current() == creator_loop_);
+
+  observers_.erase(observer);
+  if (observers_.empty())
+    Stop();
+}
+
+void ProviderImpl::Start() {
+  DCHECK(MessageLoop::current() == creator_loop_);
+  DCHECK(!polling_thread_.get());
+
+  polling_thread_.reset(new base::Thread("Device orientation polling thread"));
+  if (!polling_thread_->Start()) {
+    LOG(ERROR) << "Failed to start device orientation polling thread";
+    polling_thread_.reset();
+    return;
+  }
+  ScheduleInitializePollingThread();
+}
+
+void ProviderImpl::Stop() {
+  DCHECK(MessageLoop::current() == creator_loop_);
+  polling_thread_.reset();
+  data_fetcher_.reset();
+}
+
+void ProviderImpl::DoInitializePollingThread(
+    std::vector<DataFetcherFactory> factories) {
+  DCHECK(MessageLoop::current() == polling_thread_->message_loop());
+
+  typedef std::vector<DataFetcherFactory>::const_iterator Iterator;
+  for (Iterator i = factories_.begin(), e = factories_.end(); i != e; ++i) {
+    DataFetcherFactory factory = *i;
+    scoped_ptr<DataFetcher> fetcher(factory());
+    Orientation orientation;
+
+    if (fetcher.get() && fetcher->GetOrientation(&orientation)) {
+      // Pass ownership of fetcher to provider_.
+      data_fetcher_.swap(fetcher);
+      last_orientation_ = orientation;
+
+      // Notify observers.
+      ScheduleDoNotify(orientation);
+
+      // Start polling.
+      ScheduleDoPoll();
+      return;
+    }
+  }
+
+  // When no orientation data can be provided.
+  ScheduleDoNotify(Orientation::Empty());
+}
+
+void ProviderImpl::ScheduleInitializePollingThread() {
+  DCHECK(MessageLoop::current() == creator_loop_);
+
+  Task* task = NewRunnableMethod(this,
+                                 &ProviderImpl::DoInitializePollingThread,
+                                 factories_);
+  MessageLoop* polling_loop = polling_thread_->message_loop();
+  polling_loop->PostTask(FROM_HERE, task);
+}
+
+void ProviderImpl::DoNotify(Orientation orientation) {
+  DCHECK(MessageLoop::current() == creator_loop_);
+
+  last_notification_ = orientation;
+
+  typedef std::set<Observer*>::const_iterator Iterator;
+  for (Iterator i = observers_.begin(), e = observers_.end(); i != e; ++i)
+    (*i)->OnOrientationUpdate(orientation);
+
+  if (orientation.IsEmpty()) {
+    // Notify observers about failure to provide data exactly once.
+    observers_.clear();
+    Stop();
+  }
+}
+
+void ProviderImpl::ScheduleDoNotify(Orientation orientation) {
+  DCHECK(MessageLoop::current() == polling_thread_->message_loop());
+
+  Task* task = NewRunnableMethod(this, &ProviderImpl::DoNotify, orientation);
+  creator_loop_->PostTask(FROM_HERE, task);
+}
+
+void ProviderImpl::DoPoll() {
+  DCHECK(MessageLoop::current() == polling_thread_->message_loop());
+
+  Orientation orientation;
+  if (!data_fetcher_->GetOrientation(&orientation)) {
+    LOG(ERROR) << "Failed to poll device orientation data fetcher.";
+
+    ScheduleDoNotify(Orientation::Empty());
+    return;
+  }
+
+  if (SignificantlyDifferent(orientation, last_orientation_)) {
+    last_orientation_ = orientation;
+    ScheduleDoNotify(orientation);
+  }
+
+  ScheduleDoPoll();
+}
+
+void ProviderImpl::ScheduleDoPoll() {
+  DCHECK(MessageLoop::current() == polling_thread_->message_loop());
+
+  Task* task = do_poll_method_factory_.NewRunnableMethod(&ProviderImpl::DoPoll);
+  MessageLoop* polling_loop = polling_thread_->message_loop();
+  polling_loop->PostDelayedTask(FROM_HERE, task, SamplingIntervalMs());
+}
+
+namespace {
+bool IsElementSignificantlyDifferent(bool can_provide_element1,
+                                     bool can_provide_element2,
+                                     double element1,
+                                     double element2) {
+  const double kThreshold = 0.1;
+
+  if (can_provide_element1 != can_provide_element2)
+    return true;
+  if (can_provide_element1 &&
+      std::fabs(element1 - element2) >= kThreshold)
+    return true;
+  return false;
+}
+} // namespace
+
+// Returns true if two orientations are considered different enough that
+// observers should be notified of the new orientation.
+bool ProviderImpl::SignificantlyDifferent(const Orientation& o1,
+                                          const Orientation& o2) {
+  return IsElementSignificantlyDifferent(o1.can_provide_alpha_,
+                                         o2.can_provide_alpha_,
+                                         o1.alpha_,
+                                         o2.alpha_) ||
+      IsElementSignificantlyDifferent(o1.can_provide_beta_,
+                                         o2.can_provide_beta_,
+                                         o1.beta_,
+                                         o2.beta_) ||
+      IsElementSignificantlyDifferent(o1.can_provide_gamma_,
+                                         o2.can_provide_gamma_,
+                                         o1.gamma_,
+                                         o2.gamma_);
+}
+
+int ProviderImpl::SamplingIntervalMs() const {
+  DCHECK(MessageLoop::current() == polling_thread_->message_loop());
+  DCHECK(data_fetcher_.get());
+
+  int fetcher_interval = data_fetcher_->MinSamplingIntervalMs();
+
+  if (fetcher_interval > kDesiredSamplingIntervalMs)
+    return fetcher_interval;
+  else
+    return kDesiredSamplingIntervalMs;
+}
+
+}  // namespace device_orientation