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