chrome/browser/usb/usb_context.cc

   1 // Copyright 2013 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "chrome/browser/usb/usb_context.h"
   6
   7 #include "base/logging.h"
   8 #include "base/synchronization/waitable_event.h"
   9 #include "base/threading/platform_thread.h"
  10 #include "content/public/browser/browser_thread.h"
  11 #include "third_party/libusb/src/libusb/interrupt.h"
  12 #include "third_party/libusb/src/libusb/libusb.h"
  13
  14 // The UsbEventHandler works around a design flaw in the libusb interface. There
  15 // is currently no way to signal to libusb that any caller into one of the event
  16 // handler calls should return without handling any events.
  17 class UsbContext::UsbEventHandler : public base::PlatformThread::Delegate {
  18  public:
  19   explicit UsbEventHandler(libusb_context* context);
  20   virtual ~UsbEventHandler();
  21
  22   // base::PlatformThread::Delegate
  23   virtual void ThreadMain() OVERRIDE;
  24
  25  private:
  26   volatile bool running_;
  27   libusb_context* context_;
  28   base::PlatformThreadHandle thread_handle_;
  29   base::WaitableEvent start_polling_;
  30   DISALLOW_COPY_AND_ASSIGN(UsbEventHandler);
  31 };
  32
  33 UsbContext::UsbEventHandler::UsbEventHandler(libusb_context* context)
  34     : running_(true),
  35       context_(context),
  36       thread_handle_(0),
  37       start_polling_(false, false) {
  38   bool success = base::PlatformThread::Create(0, this, &thread_handle_);
  39   DCHECK(success) << "Failed to create USB IO handling thread.";
  40   start_polling_.Wait();
  41 }
  42
  43 UsbContext::UsbEventHandler::~UsbEventHandler() {
  44   running_ = false;
  45   // Spreading running_ to the UsbEventHandler thread.
  46   base::subtle::MemoryBarrier();
  47   libusb_interrupt_handle_event(context_);
  48   base::PlatformThread::Join(thread_handle_);
  49 }
  50
  51 void UsbContext::UsbEventHandler::ThreadMain() {
  52   base::PlatformThread::SetName("UsbEventHandler");
  53   VLOG(1) << "UsbEventHandler started.";
  54   if (running_) {
  55     start_polling_.Signal();
  56     libusb_handle_events(context_);
  57   }
  58   while (running_)
  59     libusb_handle_events(context_);
  60   VLOG(1) << "UsbEventHandler shutting down.";
  61 }
  62
  63 UsbContext::UsbContext(PlatformUsbContext context) : context_(context) {
  64   DCHECK(thread_checker_.CalledOnValidThread());
  65   event_handler_ = new UsbEventHandler(context_);
  66 }
  67
  68 UsbContext::~UsbContext() {
  69   // destruction of UsbEventHandler is a blocking operation.
  70   DCHECK(thread_checker_.CalledOnValidThread());
  71   delete event_handler_;
  72   event_handler_ = NULL;
  73   libusb_exit(context_);
  74 }