base/win/object_watcher.cc

   1 // Copyright (c) 2012 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 "base/win/object_watcher.h"
   6
   7 #include "base/bind.h"
   8 #include "base/logging.h"
   9
  10 namespace base {
  11 namespace win {
  12
  13 //-----------------------------------------------------------------------------
  14
  15 ObjectWatcher::ObjectWatcher()
  16     : weak_factory_(this),
  17       object_(NULL),
  18       wait_object_(NULL),
  19       origin_loop_(NULL) {
  20 }
  21
  22 ObjectWatcher::~ObjectWatcher() {
  23   StopWatching();
  24 }
  25
  26 bool ObjectWatcher::StartWatching(HANDLE object, Delegate* delegate) {
  27   CHECK(delegate);
  28   if (wait_object_) {
  29     NOTREACHED() << "Already watching an object";
  30     return false;
  31   }
  32
  33   // Since our job is to just notice when an object is signaled and report the
  34   // result back to this thread, we can just run on a Windows wait thread.
  35   DWORD wait_flags = WT_EXECUTEINWAITTHREAD | WT_EXECUTEONLYONCE;
  36
  37   // DoneWaiting can be synchronously called from RegisterWaitForSingleObject,
  38   // so set up all state now.
  39   callback_ = base::Bind(&ObjectWatcher::Signal, weak_factory_.GetWeakPtr(),
  40                          delegate);
  41   object_ = object;
  42   origin_loop_ = MessageLoop::current();
  43
  44   if (!RegisterWaitForSingleObject(&wait_object_, object, DoneWaiting,
  45                                    this, INFINITE, wait_flags)) {
  46     DPLOG(FATAL) << "RegisterWaitForSingleObject failed";
  47     object_ = NULL;
  48     wait_object_ = NULL;
  49     return false;
  50   }
  51
  52   // We need to know if the current message loop is going away so we can
  53   // prevent the wait thread from trying to access a dead message loop.
  54   MessageLoop::current()->AddDestructionObserver(this);
  55   return true;
  56 }
  57
  58 bool ObjectWatcher::StopWatching() {
  59   if (!wait_object_)
  60     return false;
  61
  62   // Make sure ObjectWatcher is used in a single-threaded fashion.
  63   DCHECK_EQ(origin_loop_, MessageLoop::current());
  64
  65   // Blocking call to cancel the wait. Any callbacks already in progress will
  66   // finish before we return from this call.
  67   if (!UnregisterWaitEx(wait_object_, INVALID_HANDLE_VALUE)) {
  68     DPLOG(FATAL) << "UnregisterWaitEx failed";
  69     return false;
  70   }
  71
  72   weak_factory_.InvalidateWeakPtrs();
  73   object_ = NULL;
  74   wait_object_ = NULL;
  75
  76   MessageLoop::current()->RemoveDestructionObserver(this);
  77   return true;
  78 }
  79
  80 HANDLE ObjectWatcher::GetWatchedObject() {
  81   return object_;
  82 }
  83
  84 // static
  85 void CALLBACK ObjectWatcher::DoneWaiting(void* param, BOOLEAN timed_out) {
  86   DCHECK(!timed_out);
  87
  88   // The destructor blocks on any callbacks that are in flight, so we know that
  89   // that is always a pointer to a valid ObjectWater.
  90   ObjectWatcher* that = static_cast<ObjectWatcher*>(param);
  91   that->origin_loop_->PostTask(FROM_HERE, that->callback_);
  92   that->callback_.Reset();
  93 }
  94
  95 void ObjectWatcher::Signal(Delegate* delegate) {
  96   // Signaling the delegate may result in our destruction or a nested call to
  97   // StartWatching(). As a result, we save any state we need and clear previous
  98   // watcher state before signaling the delegate.
  99   HANDLE object = object_;
 100   StopWatching();
 101   delegate->OnObjectSignaled(object);
 102 }
 103
 104 void ObjectWatcher::WillDestroyCurrentMessageLoop() {
 105   // Need to shutdown the watch so that we don't try to access the MessageLoop
 106   // after this point.
 107   StopWatching();
 108 }
 109
 110 }  // namespace win
 111 }  // namespace base