Experimental USB API

chrome/browser/extensions/api/usb/usb_device_resource.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_EXTENSIONS_API_USB_USB_DEVICE_RESOURCE_H_
+#define CHROME_BROWSER_EXTENSIONS_API_USB_USB_DEVICE_RESOURCE_H_
+#pragma once
+
+#include <set>
+
+#include "base/basictypes.h"
+#include "base/memory/linked_ptr.h"
+#include "base/synchronization/lock.h"
+#include "chrome/browser/extensions/api/api_resource.h"
+#include "chrome/common/extensions/api/experimental.usb.h"
+
+class UsbDevice;
+
+namespace net {
+class IOBuffer;
+}  // namespace net
+
+namespace extensions {
+
+class APIResourceEventNotifier;
+
+// A UsbDeviceResource is an APIResource wrapper for a UsbDevice. When invoking
+// transfers on the underlying device it will use the APIResourceEventNotifier
+// associated with the underlying APIResource to deliver completion messages.
+class UsbDeviceResource : public APIResource {
+ public:
+  UsbDeviceResource(APIResourceEventNotifier* notifier, UsbDevice* device);
+  virtual ~UsbDeviceResource();
+
+  // All of the *Transfer variants that are exposed here adapt their arguments
+  // for the underlying UsbDevice's interface and invoke the corresponding
+  // methods with completion callbacks that call OnTransferComplete on the event
+  // notifier.
+  void ControlTransfer(
+      const api::experimental_usb::ControlTransferInfo& transfer);
+  void InterruptTransfer(
+      const api::experimental_usb::GenericTransferInfo& transfer);
+  void BulkTransfer(const api::experimental_usb::GenericTransferInfo& transfer);
+
+ private:
+  // Invoked by the underlying device's transfer callbacks. Indicates transfer
+  // completion to the APIResource's event notifier.
+  void TransferComplete(net::IOBuffer* buffer, const size_t length,
+                        int success);
+
+  scoped_refptr<UsbDevice> device_;
+
+  // pending_transfers_ is used to track the number of transfers that are
+  // currently in flight. Access to pending_transfers_ is protected by lock_.
+  base::Lock lock_;

[asargent_no_longer_on_chrome, 2012/04/26 21:21:45]

Danger Will Robinson! We almost never want to do explicit locking. I will
comment more in the .cc file where you're using this....

...ok, looks like you don't actually use it, so you can just remove.

We usually prefer to just do operations to a piece of state on a given thread
(UI,FILE, etc.), possibly using PostTask to transfer ownership over to another
thread to do some work and then having a control flow there that eventually
PostTask's back to the original thread. The most common pattern is to start on
the UI thread, post a task to do some work on the FILE thread, and then post a
task back to the UI thread.

[Garret Kelly, 2012/04/27 00:32:35]

Hmm, then perhaps I need to do a bit more thinking about the design of the
UsbService going forward. It has its own thread that drives event handling
(thanks to Windows, otherwise this would all live as a set of watched fds in the
IO thread), so finishing a transfer will be performed there. Since I'm not doing
in-flight transfer tracking in this CL I'll just remove it for now and work on
it later.

+  int pending_transfers_;
+
+  DISALLOW_EVIL_CONSTRUCTORS(UsbDeviceResource);

[asargent_no_longer_on_chrome, 2012/04/26 21:21:45]

nit: I think the synonym DISALLOW_COPY_AND_ASSIGN is the preferred macro these
days

[Garret Kelly, 2012/04/27 00:32:35]

Oh yeah, I'd forgotten about that. Done.

+};
+
+}  // namespace extensions
+
+#endif  // CHROME_BROWSER_EXTENSIONS_API_USB_USB_DEVICE_RESOURCE_H_