add device notification to Mac

content/browser/device_monitor_mac.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 "content/browser/device_monitor_mac.h"
+
+#include <IOKit/usb/IOUSBLib.h>
+
+#include "base/logging.h"
+#include "base/mac/scoped_cftyperef.h"
+#include "base/mac/scoped_ioobject.h"
+
+namespace content {
+
+namespace {
+
+struct {

[no longer working on chromium, 2012/08/08 09:23:16]

We can't use const struct here because we need to pass the memory of device_type
to the callback, see line 127
static_cast<void*>(&kDeviceServices[i].device_type).

The purposes of doing this:
# Tell what kind of device has been changed.
# Use one single callback to handle different services, in favor of avoiding
dupped code.

[Mark Mentovai, 2012/08/08 12:38:03]

That’s exactly the problem I was illustrating. It makes it way too easy for the
callback to accidentally change this table.

Why are you passing the address? The callback only needs to see the value.

+  base::SystemMonitor::DeviceType device_type;
+  const io_name_t service_type;
+} kDeviceServices[] = {
+  // Add new services here if needed.
+  { base::SystemMonitor::DEVTYPE_AUDIO_CAPTURE, kIOMatchedNotification },
+  { base::SystemMonitor::DEVTYPE_AUDIO_CAPTURE, kIOTerminatedNotification },
+  { base::SystemMonitor::DEVTYPE_VIDEO_CAPTURE, kIOMatchedNotification },
+  { base::SystemMonitor::DEVTYPE_VIDEO_CAPTURE, kIOTerminatedNotification },
+};
+
+CFMutableDictionaryRef CreateMatchingDictionary(
+    SInt32 interface_class_code, SInt32 interface_subclass_code) {
+  CFMutableDictionaryRef matching_dictionary = IOServiceMatching(
+      kIOUSBInterfaceClassName);
+  base::mac::ScopedCFTypeRef<CFNumberRef> number_ref(CFNumberCreate(
+      kCFAllocatorDefault, kCFNumberSInt32Type, &interface_class_code));
+  DCHECK(number_ref);
+  CFDictionaryAddValue(matching_dictionary, CFSTR(kUSBInterfaceClass),
+                       number_ref);
+
+  number_ref.reset(CFNumberCreate(kCFAllocatorDefault,
+                                  kCFNumberSInt32Type,
+                                  &interface_subclass_code));
+  DCHECK(number_ref);
+  CFDictionaryAddValue(matching_dictionary, CFSTR(kUSBInterfaceSubClass),
+                       number_ref);
+
+  return matching_dictionary;
+}
+
+void AddCallbackToIOService(IONotificationPortRef port,
+                            const io_name_t type,
+                            CFMutableDictionaryRef dictionary,
+                            IOServiceMatchingCallback callback,
+                            void* context,
+                            io_iterator_t* notification) {
+   kern_return_t err = IOServiceAddMatchingNotification(port,
+                                                        type,
+                                                        dictionary,
+                                                        callback,
+                                                        context,
+                                                        notification);
+  if (err) {
+    NOTREACHED() << "Failed to register the IO matched notification for type "
+                 << type;
+    return;
+  }
+  DCHECK(*notification);
+
+  // Iterate over set of matching devices to access already-present devices
+  // and to arm the notification.
+  base::mac::ScopedIOObject<io_service_t> this_object(
+      IOIteratorNext(*notification));
+  for (; this_object; this_object.reset(IOIteratorNext(*notification)));
+}
+
+}  // namespace
+
+DeviceMonitorMac::DeviceMonitorMac() {
+
+  // Add the notification port to the run loop.
+  notification_port_ = IONotificationPortCreate(kIOMasterPortDefault);
+  DCHECK(notification_port_);
+
+  RegisterServices();
+
+  CFRunLoopAddSource(CFRunLoopGetCurrent(),
+                     IONotificationPortGetRunLoopSource(notification_port_),
+                     kCFRunLoopCommonModes);
+}
+
+DeviceMonitorMac::~DeviceMonitorMac() {
+  // Stop the notifications and free the objects.
+  for (size_t i = 0; i < arraysize(kDeviceServices); ++i) {
+    IOObjectRelease(notification_iterators_[i]);
+  }
+
+  // Remove the sleep notification port from the application runloop.
+  CFRunLoopRemoveSource(CFRunLoopGetCurrent(),
+                        IONotificationPortGetRunLoopSource(notification_port_),
+                        kCFRunLoopCommonModes);
+
+  // Destroy the notification port allocated by IONotificationPortCreate.
+  IONotificationPortDestroy(notification_port_);
+}
+
+void DeviceMonitorMac::RegisterServices() {
+  notification_iterators_.reset(new io_iterator_t[arraysize(kDeviceServices)]);
+  CFMutableDictionaryRef matching_dictionary;
+  for (size_t i = 0; i < arraysize(kDeviceServices); ++i) {
+    switch (kDeviceServices[i].device_type) {
+      case base::SystemMonitor::DEVTYPE_AUDIO_CAPTURE:
+        matching_dictionary = CreateMatchingDictionary(
+            kUSBAudioInterfaceClass, kUSBAudioControlSubClass);
+        break;
+      case base::SystemMonitor::DEVTYPE_VIDEO_CAPTURE:
+        matching_dictionary = CreateMatchingDictionary(
+            kUSBVideoInterfaceClass, kUSBVideoControlSubClass);
+        break;
+      default:
+        NOTREACHED();
+        return;
+    }
+
+    // Add callback to the service.
+    AddCallbackToIOService(notification_port_,
+                           kDeviceServices[i].service_type,
+                           matching_dictionary,
+                           &DeviceChangedCallback,
+                           static_cast<void*>(&kDeviceServices[i].device_type),
+                           &notification_iterators_[i]);
+  }
+}
+
+void DeviceMonitorMac::DeviceChangedCallback(void *context,
+                                             io_iterator_t iterator) {
+  base::mac::ScopedIOObject<io_service_t> this_object(IOIteratorNext(iterator));
+  for (; this_object; this_object.reset(IOIteratorNext(iterator))) {
+    if (context) {
+      base::SystemMonitor::DeviceType device_type =
+          *reinterpret_cast<base::SystemMonitor::DeviceType*>(context);
+      DCHECK(device_type == base::SystemMonitor::DEVTYPE_AUDIO_CAPTURE ||
+             device_type == base::SystemMonitor::DEVTYPE_VIDEO_CAPTURE);
+      // TODO(xians): Remove the global variable for SystemMonitor.
+      base::SystemMonitor::Get()->ProcessDevicesChanged(device_type);
+    }
+  }
+}
+
+}  // namespace content