Manage UsbService lifetime in DeviceClient implementations.

device/usb/usb_service.cc

 // Copyright 2015 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 "device/usb/usb_service.h"
 
 #include "base/at_exit.h"
 #include "base/bind.h"
 #include "components/device_event_log/device_event_log.h"
 #include "device/usb/usb_device.h"
 #include "device/usb/usb_service_impl.h"
 
 namespace device {
 
-namespace {
-
-UsbService* g_service;
-
-}  // namespace
-
 UsbService::Observer::~Observer() {}
 
 void UsbService::Observer::OnDeviceAdded(scoped_refptr<UsbDevice> device) {
 }
 
 void UsbService::Observer::OnDeviceRemoved(scoped_refptr<UsbDevice> device) {
 }
 
 void UsbService::Observer::OnDeviceRemovedCleanup(
     scoped_refptr<UsbDevice> device) {
 }
 
 // static
-UsbService* UsbService::GetInstance(
+scoped_ptr<UsbService> UsbService::Create(
     scoped_refptr<base::SequencedTaskRunner> blocking_task_runner) {
-  if (!g_service) {
-    // |g_service| is set by the UsbService constructor.
-    new UsbServiceImpl(blocking_task_runner);
-    if (!g_service) {
-      base::AtExitManager::RegisterTask(base::Bind(
-          &base::DeletePointer<UsbService>, base::Unretained(g_service)));
-    }
-  }
-  return g_service;
+  return make_scoped_ptr(new UsbServiceImpl(blocking_task_runner));
 }
 
-UsbService::UsbService() {
-  DCHECK(!g_service);
-  g_service = this;
-}
+UsbService::~UsbService() {}
 
-UsbService::~UsbService() {
-  DCHECK(g_service);
-  g_service = nullptr;
-}
+UsbService::UsbService() {}
 
 void UsbService::AddObserver(Observer* observer) {
   DCHECK(CalledOnValidThread());
   observer_list_.AddObserver(observer);
 }
 
 void UsbService::RemoveObserver(Observer* observer) {
   DCHECK(CalledOnValidThread());
   observer_list_.RemoveObserver(observer);
 }
 
 void UsbService::NotifyDeviceAdded(scoped_refptr<UsbDevice> device) {
   DCHECK(CalledOnValidThread());
 
   FOR_EACH_OBSERVER(Observer, observer_list_, OnDeviceAdded(device));
 }
 
 void UsbService::NotifyDeviceRemoved(scoped_refptr<UsbDevice> device) {
   DCHECK(CalledOnValidThread());
 
   FOR_EACH_OBSERVER(Observer, observer_list_, OnDeviceRemoved(device));
   FOR_EACH_OBSERVER(Observer, observer_list_, OnDeviceRemovedCleanup(device));
 }
 
 }  // namespace device