Adding UsbService and UsbDevice constructs.

chrome/browser/usb/usb_service.h

+// 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.
+
+#ifndef CHROME_BROWSER_USB_USB_SERVICE_H_
+#define CHROME_BROWSER_USB_USB_SERVICE_H_
+#pragma once
+
+#include <map>
+#include <utility>
+
+#include "base/basictypes.h"
+#include "base/threading/thread.h"
+#include "chrome/browser/usb/usb_device.h"
+#include "third_party/libusb/libusb/libusb.h"
+
+typedef libusb_context *PlatformUsbContext;
+
+// The USB service handles creating and managing an event handler thread that is
+// used to manage and dispatch USB events. It is also responsbile for device
+// discovery on the system, which allows it to re-use device handles to prevent
+// competition for the same USB device.
+class UsbService {

[Elliot Glaysher, 2012/04/25 21:10:20]

Is it safe if there are multiple UsbServices? When you make something attached
to the Profile, you assert that you can have one per open profile.

+ public:
+  UsbService();
+  virtual ~UsbService();
+
+  // Cleanup must be invoked before the service is destroyed. It interrupts the
+  // event handling thread and disposes of open devices.
+  void Cleanup();
+
+  // Find the (topologically) first USB device identified by vendor_id and
+  // product_id. The created device is associated with this service, so that
+  // it can be used to close the device later.
+  UsbDevice *FindDevice(const uint16 vendor_id, const uint16 product_id);

[miket_OOO, 2012/04/25 21:24:36]

Why const a primitive parameter? (not entirely a rhetorical question; I believe
it's a no-op, but happy to learn something.)

[Garret Kelly, 2012/04/26 02:21:42]

My justification's a little weak. :)

I'm in the habit of const'ing everything in sight, especially in the case of
function parameters. If a function is called to deal with a specific set of
inputs I find it easier to think about the inputs as being fixed for the
duration of the call.

+
+  // This function should not be called by normal code. It is invoked by a
+  // UsbDevice's Close function and disposes of the associated platform handle.
+  void CloseDevice(scoped_refptr<UsbDevice> device);
+
+ private:
+  // Posts a HandleEvent task to the event handling thread.
+  void PostHandleEventTask();
+
+  // Handles a single USB event. If the service is still running after the event
+  // is handled, posts another HandleEvent callback to the thread.
+  void HandleEvent();
+
+  // Shutdown is invoked after event handling has been suspended and is used to
+  // free the platform resources associated with the service.
+  void Shutdown();
+
+  bool running_;
+  PlatformUsbContext context_;
+  base::Thread thread_;
+
+  // The devices_ map contains scoped_refptrs to all open devices, indicated by
+  // their vendor and product id. This allows for reusing an open device without
+  // creating another platform handle for it.
+  typedef std::map<std::pair<uint16, uint16>, scoped_refptr<UsbDevice> >
+      DeviceMap;
+  DeviceMap devices_;
+
+  DISALLOW_EVIL_CONSTRUCTORS(UsbService);
+};
+
+#endif  // CHROME_BROWSER_USB_USB_SERVICE_H_