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// Copyright 2012 The Chromium Authors
// 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 <windows.h>
#include <utility>
#include "base/functional/bind.h"
#include "base/logging.h"
#include "base/synchronization/waitable_event.h"
#include "base/task/sequenced_task_runner.h"
#include "base/threading/thread_restrictions.h"
#include "base/trace_event/trace_event.h"
namespace base {
namespace win {
//-----------------------------------------------------------------------------
ObjectWatcher::ObjectWatcher() = default;
ObjectWatcher::~ObjectWatcher() {
StopWatching();
}
bool ObjectWatcher::StartWatchingOnce(HANDLE object,
Delegate* delegate,
const Location& from_here) {
return StartWatchingInternal(object, delegate, true, from_here);
}
bool ObjectWatcher::StartWatchingMultipleTimes(HANDLE object,
Delegate* delegate,
const Location& from_here) {
return StartWatchingInternal(object, delegate, false, from_here);
}
bool ObjectWatcher::StopWatching() {
if (!wait_object_) {
return false;
}
// Make sure ObjectWatcher is used in a sequenced fashion.
DCHECK(task_runner_->RunsTasksInCurrentSequence());
// Allow blocking calls for historical reasons; see https://crbug.com/700335.
base::ScopedAllowBaseSyncPrimitivesOutsideBlockingScope allow_blocking;
// Cancel the wait; blocking on it being unregistered. Note that passing
// INVALID_HANDLE_VALUE to wait on all callback functions seemlingly waits
// on other callbacks in the threadpool; not just callbacks from
// RegisterWaitForSingleObject.
{
// Measure the total cost of calling UnregisterWaitEx, including creation of
// and waiting on the event.
TRACE_EVENT("base", "UnregisterWaitEx");
WaitableEvent event;
if (!UnregisterWaitEx(wait_object_, event.handle())) {
// ERROR_IO_PENDING is not a fatal error; see
// https://learn.microsoft.com/en-us/windows/win32/sync/unregisterwaitex.
if (const auto error = ::GetLastError(); error != ERROR_IO_PENDING) {
DPLOG(FATAL) << "UnregisterWaitEx failed";
return false;
}
}
// Wait for unregistration to complete.
event.Wait();
}
Reset();
return true;
}
bool ObjectWatcher::IsWatching() const {
return object_ != nullptr;
}
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` must not be touched once `PostTask` returns since the callback
// could delete the instance on another thread.
SequencedTaskRunner* const task_runner = that->task_runner_.get();
if (that->run_once_) {
task_runner->PostTask(that->location_, std::move(that->callback_));
} else {
task_runner->PostTask(that->location_, that->callback_);
}
}
bool ObjectWatcher::StartWatchingInternal(HANDLE object,
Delegate* delegate,
bool execute_only_once,
const Location& from_here) {
DCHECK(delegate);
DCHECK(!wait_object_) << "Already watching an object";
DCHECK(SequencedTaskRunner::HasCurrentDefault());
location_ = from_here;
task_runner_ = SequencedTaskRunner::GetCurrentDefault();
run_once_ = execute_only_once;
// Since our job is to just notice when an object is signaled and report the
// result back to this sequence, we can just run on a Windows wait thread.
DWORD wait_flags = WT_EXECUTEINWAITTHREAD;
if (run_once_) {
wait_flags |= WT_EXECUTEONLYONCE;
}
// DoneWaiting can be synchronously called from RegisterWaitForSingleObject,
// so set up all state now.
callback_ = BindRepeating(&ObjectWatcher::Signal, weak_factory_.GetWeakPtr(),
// For all non-test usages, the delegate's lifetime
// exceeds object_watcher's. This should be safe.
base::UnsafeDanglingUntriaged(delegate));
object_ = object;
TRACE_EVENT("base", "RegisterWaitForSingleObject");
if (!RegisterWaitForSingleObject(&wait_object_, object, DoneWaiting, this,
INFINITE, wait_flags)) {
DPLOG(FATAL) << "RegisterWaitForSingleObject failed";
Reset();
return false;
}
return true;
}
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_;
if (run_once_) {
StopWatching();
}
delegate->OnObjectSignaled(object);
}
void ObjectWatcher::Reset() {
callback_.Reset();
location_ = {};
object_ = nullptr;
wait_object_ = nullptr;
task_runner_ = nullptr;
run_once_ = true;
weak_factory_.InvalidateWeakPtrs();
}
} // namespace win
} // namespace base
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