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/threading/simple_thread.h"
  10 #include "device/usb/usb_error.h"
  11 #include "third_party/libusb/src/libusb/interrupt.h"
  12 #include "third_party/libusb/src/libusb/libusb.h"
  13
  14 namespace device {
  15
  16 // The UsbEventHandler works around a design flaw in the libusb interface. There
  17 // is currently no way to signal to libusb that any caller into one of the event
  18 // handler calls should return without handling any events.
  19 class UsbContext::UsbEventHandler : public base::SimpleThread {
  20  public:
  21   explicit UsbEventHandler(libusb_context* context);
  22   ~UsbEventHandler() override;
  23
  24   // base::SimpleThread
  25   void Run() override;
  26
  27   void Stop();
  28
  29  private:
  30   base::subtle::Atomic32 running_;
  31   libusb_context* context_;
  32   DISALLOW_COPY_AND_ASSIGN(UsbEventHandler);
  33 };
  34
  35 UsbContext::UsbEventHandler::UsbEventHandler(libusb_context* context)
  36     : base::SimpleThread("UsbEventHandler"), context_(context) {
  37   base::subtle::Release_Store(&running_, 1);
  38 }
  39
  40 UsbContext::UsbEventHandler::~UsbEventHandler() {
  41   libusb_exit(context_);
  42 }
  43
  44 void UsbContext::UsbEventHandler::Run() {
  45   VLOG(1) << "UsbEventHandler started.";
  46
  47   while (base::subtle::Acquire_Load(&running_)) {
  48     const int rv = libusb_handle_events(context_);
  49     if (rv != LIBUSB_SUCCESS) {
  50       VLOG(1) << "Failed to handle events: "
  51               << ConvertPlatformUsbErrorToString(rv);
  52     }
  53   }
  54
  55   VLOG(1) << "UsbEventHandler shutting down.";
  56 }
  57
  58 void UsbContext::UsbEventHandler::Stop() {
  59   base::subtle::Release_Store(&running_, 0);
  60   libusb_interrupt_handle_event(context_);
  61 }
  62
  63 UsbContext::UsbContext(PlatformUsbContext context) : context_(context) {
  64   // Ownership of the PlatformUsbContext is passed to the event handler thread.
  65   event_handler_.reset(new UsbEventHandler(context_));
  66   event_handler_->Start();
  67 }
  68
  69 UsbContext::~UsbContext() {
  70   DCHECK(thread_checker_.CalledOnValidThread());
  71   event_handler_->Stop();
  72   event_handler_->Join();
  73 }
  74
  75 }  // namespace device