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/logging.h"
   8 #include "base/synchronization/waitable_event.h"
   9 #include "base/threading/platform_thread.h"
  10 #include "third_party/libusb/src/libusb/interrupt.h"
  11 #include "third_party/libusb/src/libusb/libusb.h"
  12
  13 namespace usb_service {
  14
  15 // The UsbEventHandler works around a design flaw in the libusb interface. There
  16 // is currently no way to signal to libusb that any caller into one of the event
  17 // handler calls should return without handling any events.
  18 class UsbContext::UsbEventHandler : public base::PlatformThread::Delegate {
  19  public:
  20   explicit UsbEventHandler(libusb_context* context);
  21   virtual ~UsbEventHandler();
  22
  23   // base::PlatformThread::Delegate
  24   virtual void ThreadMain() OVERRIDE;
  25
  26  private:
  27   volatile bool running_;
  28   libusb_context* context_;
  29   base::PlatformThreadHandle thread_handle_;
  30   base::WaitableEvent start_polling_;
  31   DISALLOW_COPY_AND_ASSIGN(UsbEventHandler);
  32 };
  33
  34 UsbContext::UsbEventHandler::UsbEventHandler(libusb_context* context)
  35     : running_(true),
  36       context_(context),
  37       thread_handle_(0),
  38       start_polling_(false, false) {
  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   running_ = false;
  46   // Spreading running_ to the UsbEventHandler thread.
  47   base::subtle::MemoryBarrier();
  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   if (running_) {
  56     start_polling_.Signal();
  57     libusb_handle_events(context_);
  58   }
  59   while (running_)
  60     libusb_handle_events(context_);
  61   VLOG(1) << "UsbEventHandler shutting down.";
  62 }
  63
  64 UsbContext::UsbContext(PlatformUsbContext context) : context_(context) {
  65   DCHECK(thread_checker_.CalledOnValidThread());
  66   event_handler_ = new UsbEventHandler(context_);
  67 }
  68
  69 UsbContext::~UsbContext() {
  70   // destruction of UsbEventHandler is a blocking operation.
  71   DCHECK(thread_checker_.CalledOnValidThread());
  72   delete event_handler_;
  73   event_handler_ = NULL;
  74   libusb_exit(context_);
  75 }
  76
  77 }  // namespace usb_service