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// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "base/win/object_watcher.h"
#include "base/bind.h"
#include "base/logging.h"
namespace base {
namespace win {
//-----------------------------------------------------------------------------
ObjectWatcher::ObjectWatcher()
: object_(NULL),
wait_object_(NULL),
origin_loop_(NULL),
weak_factory_(this) {
}
ObjectWatcher::~ObjectWatcher() {
StopWatching();
}
bool ObjectWatcher::StartWatching(HANDLE object, Delegate* delegate) {
CHECK(delegate);
if (wait_object_) {
NOTREACHED() << "Already watching an object";
return false;
}
// Since our job is to just notice when an object is signaled and report the
// result back to this thread, we can just run on a Windows wait thread.
DWORD wait_flags = WT_EXECUTEINWAITTHREAD | WT_EXECUTEONLYONCE;
// DoneWaiting can be synchronously called from RegisterWaitForSingleObject,
// so set up all state now.
callback_ = base::Bind(&ObjectWatcher::Signal, weak_factory_.GetWeakPtr(),
delegate);
object_ = object;
origin_loop_ = MessageLoop::current();
if (!RegisterWaitForSingleObject(&wait_object_, object, DoneWaiting,
this, INFINITE, wait_flags)) {
DPLOG(FATAL) << "RegisterWaitForSingleObject failed";
object_ = NULL;
wait_object_ = NULL;
return false;
}
// We need to know if the current message loop is going away so we can
// prevent the wait thread from trying to access a dead message loop.
MessageLoop::current()->AddDestructionObserver(this);
return true;
}
bool ObjectWatcher::StopWatching() {
if (!wait_object_)
return false;
// Make sure ObjectWatcher is used in a single-threaded fashion.
DCHECK_EQ(origin_loop_, MessageLoop::current());
// Blocking call to cancel the wait. Any callbacks already in progress will
// finish before we return from this call.
if (!UnregisterWaitEx(wait_object_, INVALID_HANDLE_VALUE)) {
DPLOG(FATAL) << "UnregisterWaitEx failed";
return false;
}
weak_factory_.InvalidateWeakPtrs();
object_ = NULL;
wait_object_ = NULL;
MessageLoop::current()->RemoveDestructionObserver(this);
return true;
}
bool ObjectWatcher::IsWatching() const {
return object_ != NULL;
}
HANDLE ObjectWatcher::GetWatchedObject() const {
return object_;
}
// static
void CALLBACK ObjectWatcher::DoneWaiting(void* param, BOOLEAN timed_out) {
DCHECK(!timed_out);
// The destructor blocks on any callbacks that are in flight, so we know that
// that is always a pointer to a valid ObjectWater.
ObjectWatcher* that = static_cast<ObjectWatcher*>(param);
that->origin_loop_->task_runner()->PostTask(FROM_HERE, that->callback_);
that->callback_.Reset();
}
void ObjectWatcher::Signal(Delegate* delegate) {
// Signaling the delegate may result in our destruction or a nested call to
// StartWatching(). As a result, we save any state we need and clear previous
// watcher state before signaling the delegate.
HANDLE object = object_;
StopWatching();
delegate->OnObjectSignaled(object);
}
void ObjectWatcher::WillDestroyCurrentMessageLoop() {
// Need to shutdown the watch so that we don't try to access the MessageLoop
// after this point.
StopWatching();
}
} // namespace win
} // namespace base
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