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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 
UsbEventHandler(libusb_context * context)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 
~UsbEventHandler()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 
ThreadMain()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 
UsbContext(PlatformUsbContext context)67 UsbContext::UsbContext(PlatformUsbContext context) : context_(context) {
68   DCHECK(thread_checker_.CalledOnValidThread());
69   event_handler_ = new UsbEventHandler(context_);
70 }
71 
~UsbContext()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
81