Fail gracefully when libusb_init fails

chrome/browser/usb/usb_service.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/usb/usb_service.h"
 
 #include <set>
 #include <vector>
 
 #include "base/basictypes.h"
@@ skipping 46 matching lines @@
     }
   }
   UsbService* service_;
   content::NotificationRegistrar registrar_;
 };
 
 }  // namespace
 
 using content::BrowserThread;
 
-UsbService::UsbService()
-    : context_(new UsbContext()),
+UsbService::UsbService(PlatformUsbContext context)
+    : context_(new UsbContext(context)),
       next_unique_id_(0) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
   // Will be deleted upon NOTIFICATION_APP_TERMINATING.
   new ExitObserver(this);
 }
 
 UsbService::~UsbService() {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
   for (DeviceMap::iterator it = devices_.begin(); it != devices_.end(); ++it) {
     it->second->OnDisconnect();
   }
 }
 
+struct InitUsbContextTraits : public LeakySingletonTraits<UsbService> {
+  // LeakySingletonTraits<UsbService>
+  static UsbService* New() {
+    PlatformUsbContext context;
+    libusb_init(&context);
+    if (!context)

[xiyuan, 2013/09/04 20:22:22]

nit: should we check the return code of libusb_init instead of relying on it to
nullify |context|?

[Bei Zhang, 2013/09/04 21:04:58]

I see. There's chance that context is not even initialized.

On 2013/09/04 20:22:22, xiyuan wrote:

+      return NULL;
+    return new UsbService(context);
+  }
+};
+
 UsbService* UsbService::GetInstance() {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
   // UsbService deletes itself upon APP_TERMINATING.
-  return Singleton<UsbService, LeakySingletonTraits<UsbService> >::get();
+  return Singleton<UsbService, InitUsbContextTraits>::get();
 }
 
 void UsbService::GetDevices(std::vector<scoped_refptr<UsbDevice> >* devices) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
   STLClearObject(devices);
   RefreshDevices();
 
   for (DeviceMap::iterator it = devices_.begin(); it != devices_.end(); ++it) {
     devices->push_back(it->second);
   }
@@ skipping 47 matching lines @@
 
   // Remove disconnected devices from devices_.
   for (size_t i = 0; i < disconnected_devices.size(); ++i) {
     // UsbDevice will be destroyed after this. The corresponding
     // PlatformUsbDevice will be unref'ed during this process.
     devices_.erase(disconnected_devices[i]);
   }
 
   libusb_free_device_list(platform_devices, true);
 }