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/platform_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::PlatformThread::Delegate {
  20  public:
  21   explicit UsbEventHandler(libusb_context* context);
  22   ~UsbEventHandler() override;
  23
  24   // base::PlatformThread::Delegate
  25   void ThreadMain() override;
  26
  27   void Stop();
  28
  29  private:
  30   base::subtle::Atomic32 running_;
  31   libusb_context* context_;
  32   base::PlatformThreadHandle thread_handle_;
  33   DISALLOW_COPY_AND_ASSIGN(UsbEventHandler);
  34 };
  35
  36 UsbContext::UsbEventHandler::UsbEventHandler(libusb_context* context)
  37     : context_(context), thread_handle_(0) {
  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 }
  42
  43 UsbContext::UsbEventHandler::~UsbEventHandler() {
  44   libusb_exit(context_);
  45 }
  46
  47 void UsbContext::UsbEventHandler::ThreadMain() {
  48   base::PlatformThread::SetName("UsbEventHandler");
  49   VLOG(1) << "UsbEventHandler started.";
  50
  51   while (base::subtle::Acquire_Load(&running_)) {
  52     const int rv = libusb_handle_events(context_);
  53     if (rv != LIBUSB_SUCCESS) {
  54       VLOG(1) << "Failed to handle events: "
  55               << ConvertPlatformUsbErrorToString(rv);
  56     }
  57   }
  58
  59   VLOG(1) << "UsbEventHandler shutting down.";
  60   delete this;
  61 }
  62
  63 void UsbContext::UsbEventHandler::Stop() {
  64   base::subtle::Release_Store(&running_, 0);
  65   libusb_interrupt_handle_event(context_);
  66 }
  67
  68 UsbContext::UsbContext(PlatformUsbContext context) : context_(context) {
  69   // Ownership of the PlatformUsbContext is passed to the event handler thread.
  70   event_handler_ = new UsbEventHandler(context_);
  71 }
  72
  73 UsbContext::~UsbContext() {
  74   DCHECK(thread_checker_.CalledOnValidThread());
  75   event_handler_->Stop();
  76 }
  77
  78 }  // namespace device