components/usb_service/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 "components/usb_service/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 "components/usb_service/usb_error.h"
  12 #include "third_party/libusb/src/libusb/interrupt.h"
  13 #include "third_party/libusb/src/libusb/libusb.h"
  14
  15 namespace usb_service {
  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),
  38       thread_handle_(0),
  39       start_polling_(false, false) {
  40   base::subtle::Release_Store(&running_, 1);
  41   bool success = base::PlatformThread::Create(0, this, &thread_handle_);
  42   DCHECK(success) << "Failed to create USB IO handling thread.";
  43   start_polling_.Wait();
  44 }
  45
  46 UsbContext::UsbEventHandler::~UsbEventHandler() {
  47   base::subtle::Release_Store(&running_, 0);
  48   libusb_interrupt_handle_event(context_);
  49   base::PlatformThread::Join(thread_handle_);
  50 }
  51
  52 void UsbContext::UsbEventHandler::ThreadMain() {
  53   base::PlatformThread::SetName("UsbEventHandler");
  54   VLOG(1) << "UsbEventHandler started.";
  55
  56   if (base::subtle::Acquire_Load(&running_)) {
  57     start_polling_.Signal();
  58   }
  59   while (base::subtle::Acquire_Load(&running_)) {
  60     const int rv = libusb_handle_events(context_);
  61     if (rv != LIBUSB_SUCCESS) {
  62       VLOG(1) << "Failed to handle events: " << ConvertErrorToString(rv);
  63     }
  64   }
  65   VLOG(1) << "UsbEventHandler shutting down.";
  66 }
  67
  68 UsbContext::UsbContext(PlatformUsbContext context) : context_(context) {
  69   DCHECK(thread_checker_.CalledOnValidThread());
  70   event_handler_ = new UsbEventHandler(context_);
  71 }
  72
  73 UsbContext::~UsbContext() {
  74   // destruction of UsbEventHandler is a blocking operation.
  75   DCHECK(thread_checker_.CalledOnValidThread());
  76   delete event_handler_;
  77   event_handler_ = NULL;
  78   libusb_exit(context_);
  79 }
  80
  81 }  // namespace usb_service