device/usb/usb_context.cc

   1 // Copyright 2014 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 "device/usb/usb_context.h"
   6
   7 #include "base/atomicops.h"
   8 #include "base/logging.h"
   9 #include "base/synchronization/waitable_event.h"
  10 #include "base/threading/platform_thread.h"
  11 #include "device/usb/usb_error.h"
  12 #include "third_party/libusb/src/libusb/interrupt.h"
  13 #include "third_party/libusb/src/libusb/libusb.h"
  14
  15 namespace device {
  16
  17 // The UsbEventHandler works around a design flaw in the libusb interface. There
  18 // is currently no way to signal to libusb that any caller into one of the event
  19 // handler calls should return without handling any events.
  20 class UsbContext::UsbEventHandler : public base::PlatformThread::Delegate {
  21  public:
  22   explicit UsbEventHandler(libusb_context* context);
  23   virtual ~UsbEventHandler();
  24
  25   // base::PlatformThread::Delegate
  26   virtual void ThreadMain() OVERRIDE;
  27
  28  private:
  29   base::subtle::Atomic32 running_;
  30   libusb_context* context_;
  31   base::PlatformThreadHandle thread_handle_;
  32   base::WaitableEvent start_polling_;
  33   DISALLOW_COPY_AND_ASSIGN(UsbEventHandler);
  34 };
  35
  36 UsbContext::UsbEventHandler::UsbEventHandler(libusb_context* context)
  37     : context_(context), thread_handle_(0), start_polling_(false, false) {
  38   base::subtle::Release_Store(&running_, 1);
  39   bool success = base::PlatformThread::Create(0, this, &thread_handle_);
  40   DCHECK(success) << "Failed to create USB IO handling thread.";
  41   start_polling_.Wait();
  42 }
  43
  44 UsbContext::UsbEventHandler::~UsbEventHandler() {
  45   base::subtle::Release_Store(&running_, 0);
  46   libusb_interrupt_handle_event(context_);
  47   base::PlatformThread::Join(thread_handle_);
  48 }
  49
  50 void UsbContext::UsbEventHandler::ThreadMain() {
  51   base::PlatformThread::SetName("UsbEventHandler");
  52   VLOG(1) << "UsbEventHandler started.";
  53
  54   if (base::subtle::Acquire_Load(&running_)) {
  55     start_polling_.Signal();
  56   }
  57   while (base::subtle::Acquire_Load(&running_)) {
  58     const int rv = libusb_handle_events(context_);
  59     if (rv != LIBUSB_SUCCESS) {
  60       VLOG(1) << "Failed to handle events: "
  61               << ConvertPlatformUsbErrorToString(rv);
  62     }
  63   }
  64   VLOG(1) << "UsbEventHandler shutting down.";
  65 }
  66
  67 UsbContext::UsbContext(PlatformUsbContext context) : context_(context) {
  68   DCHECK(thread_checker_.CalledOnValidThread());
  69   event_handler_ = new UsbEventHandler(context_);
  70 }
  71
  72 UsbContext::~UsbContext() {
  73   // destruction of UsbEventHandler is a blocking operation.
  74   DCHECK(thread_checker_.CalledOnValidThread());
  75   delete event_handler_;
  76   event_handler_ = NULL;
  77   libusb_exit(context_);
  78 }
  79
  80 }  // namespace device