root/base/message_loop/message_pump_win.cc

DEFINITIONS

1. AddObserver
2. RemoveObserver
3. WillProcessMessage
4. DidProcessMessage
5. RunWithDispatcher
6. Quit
7. GetCurrentDelay
8. ScheduleWork
9. ScheduleDelayedWork
10. WndProcThunk
11. DoRunLoop
12. InitMessageWnd
13. WaitForWork
14. HandleWorkMessage
15. HandleTimerMessage
16. ProcessNextWindowsMessage
17. ProcessMessageHelper
18. ProcessPumpReplacementMessage
19. ScheduleWork
20. ScheduleDelayedWork
21. RegisterIOHandler
22. RegisterJobObject
23. DoRunLoop
24. WaitForWork
25. WaitForIOCompletion
26. GetIOItem
27. ProcessInternalIOItem
28. MatchCompletedIOItem
29. AddIOObserver
30. RemoveIOObserver
31. WillProcessIOEvent
32. DidProcessIOEvent
33. HandlerToKey
34. KeyToHandler

// 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/message_loop/message_pump_win.h"

#include <math.h>

#include "base/debug/trace_event.h"
#include "base/message_loop/message_loop.h"
#include "base/metrics/histogram.h"
#include "base/process/memory.h"
#include "base/strings/stringprintf.h"
#include "base/win/wrapped_window_proc.h"

namespace base {

namespace {

enum MessageLoopProblems {
  MESSAGE_POST_ERROR,
  COMPLETION_POST_ERROR,
  SET_TIMER_ERROR,
  MESSAGE_LOOP_PROBLEM_MAX,
};

}  // namespace

static const wchar_t kWndClassFormat[] = L"Chrome_MessagePumpWindow_%p";

// Message sent to get an additional time slice for pumping (processing) another
// task (a series of such messages creates a continuous task pump).
static const int kMsgHaveWork = WM_USER + 1;

//-----------------------------------------------------------------------------
// MessagePumpWin public:

void MessagePumpWin::AddObserver(MessagePumpObserver* observer) {
  observers_.AddObserver(observer);
}

void MessagePumpWin::RemoveObserver(MessagePumpObserver* observer) {
  observers_.RemoveObserver(observer);
}

void MessagePumpWin::WillProcessMessage(const MSG& msg) {
  FOR_EACH_OBSERVER(MessagePumpObserver, observers_, WillProcessEvent(msg));
}

void MessagePumpWin::DidProcessMessage(const MSG& msg) {
  FOR_EACH_OBSERVER(MessagePumpObserver, observers_, DidProcessEvent(msg));
}

void MessagePumpWin::RunWithDispatcher(
    Delegate* delegate, MessagePumpDispatcher* dispatcher) {
  RunState s;
  s.delegate = delegate;
  s.dispatcher = dispatcher;
  s.should_quit = false;
  s.run_depth = state_ ? state_->run_depth + 1 : 1;

  RunState* previous_state = state_;
  state_ = &s;

  DoRunLoop();

  state_ = previous_state;
}

void MessagePumpWin::Quit() {
  DCHECK(state_);
  state_->should_quit = true;
}

//-----------------------------------------------------------------------------
// MessagePumpWin protected:

int MessagePumpWin::GetCurrentDelay() const {
  if (delayed_work_time_.is_null())
    return -1;

  // Be careful here.  TimeDelta has a precision of microseconds, but we want a
  // value in milliseconds.  If there are 5.5ms left, should the delay be 5 or
  // 6?  It should be 6 to avoid executing delayed work too early.
  double timeout =
      ceil((delayed_work_time_ - TimeTicks::Now()).InMillisecondsF());

  // If this value is negative, then we need to run delayed work soon.
  int delay = static_cast<int>(timeout);
  if (delay < 0)
    delay = 0;

  return delay;
}

//-----------------------------------------------------------------------------
// MessagePumpForUI public:

MessagePumpForUI::MessagePumpForUI()
    : atom_(0) {
  InitMessageWnd();
}

MessagePumpForUI::~MessagePumpForUI() {
  DestroyWindow(message_hwnd_);
  UnregisterClass(MAKEINTATOM(atom_),
                  GetModuleFromAddress(&WndProcThunk));
}

void MessagePumpForUI::ScheduleWork() {
  if (InterlockedExchange(&have_work_, 1))
    return;  // Someone else continued the pumping.

  // Make sure the MessagePump does some work for us.
  BOOL ret = PostMessage(message_hwnd_, kMsgHaveWork,
                         reinterpret_cast<WPARAM>(this), 0);
  if (ret)
    return;  // There was room in the Window Message queue.

  // We have failed to insert a have-work message, so there is a chance that we
  // will starve tasks/timers while sitting in a nested message loop.  Nested
  // loops only look at Windows Message queues, and don't look at *our* task
  // queues, etc., so we might not get a time slice in such. :-(
  // We could abort here, but the fear is that this failure mode is plausibly
  // common (queue is full, of about 2000 messages), so we'll do a near-graceful
  // recovery.  Nested loops are pretty transient (we think), so this will
  // probably be recoverable.
  InterlockedExchange(&have_work_, 0);  // Clarify that we didn't really insert.
  UMA_HISTOGRAM_ENUMERATION("Chrome.MessageLoopProblem", MESSAGE_POST_ERROR,
                            MESSAGE_LOOP_PROBLEM_MAX);
}

void MessagePumpForUI::ScheduleDelayedWork(const TimeTicks& delayed_work_time) {
  //
  // We would *like* to provide high resolution timers.  Windows timers using
  // SetTimer() have a 10ms granularity.  We have to use WM_TIMER as a wakeup
  // mechanism because the application can enter modal windows loops where it
  // is not running our MessageLoop; the only way to have our timers fire in
  // these cases is to post messages there.
  //
  // To provide sub-10ms timers, we process timers directly from our run loop.
  // For the common case, timers will be processed there as the run loop does
  // its normal work.  However, we *also* set the system timer so that WM_TIMER
  // events fire.  This mops up the case of timers not being able to work in
  // modal message loops.  It is possible for the SetTimer to pop and have no
  // pending timers, because they could have already been processed by the
  // run loop itself.
  //
  // We use a single SetTimer corresponding to the timer that will expire
  // soonest.  As new timers are created and destroyed, we update SetTimer.
  // Getting a spurrious SetTimer event firing is benign, as we'll just be
  // processing an empty timer queue.
  //
  delayed_work_time_ = delayed_work_time;

  int delay_msec = GetCurrentDelay();
  DCHECK_GE(delay_msec, 0);
  if (delay_msec < USER_TIMER_MINIMUM)
    delay_msec = USER_TIMER_MINIMUM;

  // Create a WM_TIMER event that will wake us up to check for any pending
  // timers (in case we are running within a nested, external sub-pump).
  BOOL ret = SetTimer(message_hwnd_, reinterpret_cast<UINT_PTR>(this),
                      delay_msec, NULL);
  if (ret)
    return;
  // If we can't set timers, we are in big trouble... but cross our fingers for
  // now.
  // TODO(jar): If we don't see this error, use a CHECK() here instead.
  UMA_HISTOGRAM_ENUMERATION("Chrome.MessageLoopProblem", SET_TIMER_ERROR,
                            MESSAGE_LOOP_PROBLEM_MAX);
}

//-----------------------------------------------------------------------------
// MessagePumpForUI private:

// static
LRESULT CALLBACK MessagePumpForUI::WndProcThunk(
    HWND hwnd, UINT message, WPARAM wparam, LPARAM lparam) {
  switch (message) {
    case kMsgHaveWork:
      reinterpret_cast<MessagePumpForUI*>(wparam)->HandleWorkMessage();
      break;
    case WM_TIMER:
      reinterpret_cast<MessagePumpForUI*>(wparam)->HandleTimerMessage();
      break;
  }
  return DefWindowProc(hwnd, message, wparam, lparam);
}

void MessagePumpForUI::DoRunLoop() {
  // IF this was just a simple PeekMessage() loop (servicing all possible work
  // queues), then Windows would try to achieve the following order according
  // to MSDN documentation about PeekMessage with no filter):
  //    * Sent messages
  //    * Posted messages
  //    * Sent messages (again)
  //    * WM_PAINT messages
  //    * WM_TIMER messages
  //
  // Summary: none of the above classes is starved, and sent messages has twice
  // the chance of being processed (i.e., reduced service time).

  for (;;) {
    // If we do any work, we may create more messages etc., and more work may
    // possibly be waiting in another task group.  When we (for example)
    // ProcessNextWindowsMessage(), there is a good chance there are still more
    // messages waiting.  On the other hand, when any of these methods return
    // having done no work, then it is pretty unlikely that calling them again
    // quickly will find any work to do.  Finally, if they all say they had no
    // work, then it is a good time to consider sleeping (waiting) for more
    // work.

    bool more_work_is_plausible = ProcessNextWindowsMessage();
    if (state_->should_quit)
      break;

    more_work_is_plausible |= state_->delegate->DoWork();
    if (state_->should_quit)
      break;

    more_work_is_plausible |=
        state_->delegate->DoDelayedWork(&delayed_work_time_);
    // If we did not process any delayed work, then we can assume that our
    // existing WM_TIMER if any will fire when delayed work should run.  We
    // don't want to disturb that timer if it is already in flight.  However,
    // if we did do all remaining delayed work, then lets kill the WM_TIMER.
    if (more_work_is_plausible && delayed_work_time_.is_null())
      KillTimer(message_hwnd_, reinterpret_cast<UINT_PTR>(this));
    if (state_->should_quit)
      break;

    if (more_work_is_plausible)
      continue;

    more_work_is_plausible = state_->delegate->DoIdleWork();
    if (state_->should_quit)
      break;

    if (more_work_is_plausible)
      continue;

    WaitForWork();  // Wait (sleep) until we have work to do again.
  }
}

void MessagePumpForUI::InitMessageWnd() {
  // Generate a unique window class name.
  string16 class_name = StringPrintf(kWndClassFormat, this);

  HINSTANCE instance = GetModuleFromAddress(&WndProcThunk);
  WNDCLASSEX wc = {0};
  wc.cbSize = sizeof(wc);
  wc.lpfnWndProc = base::win::WrappedWindowProc<WndProcThunk>;
  wc.hInstance = instance;
  wc.lpszClassName = class_name.c_str();
  atom_ = RegisterClassEx(&wc);
  DCHECK(atom_);

  message_hwnd_ = CreateWindow(MAKEINTATOM(atom_), 0, 0, 0, 0, 0, 0,
                               HWND_MESSAGE, 0, instance, 0);
  DCHECK(message_hwnd_);
}

void MessagePumpForUI::WaitForWork() {
  // Wait until a message is available, up to the time needed by the timer
  // manager to fire the next set of timers.
  int delay = GetCurrentDelay();
  if (delay < 0)  // Negative value means no timers waiting.
    delay = INFINITE;

  DWORD result;
  result = MsgWaitForMultipleObjectsEx(0, NULL, delay, QS_ALLINPUT,
                                       MWMO_INPUTAVAILABLE);

  if (WAIT_OBJECT_0 == result) {
    // A WM_* message is available.
    // If a parent child relationship exists between windows across threads
    // then their thread inputs are implicitly attached.
    // This causes the MsgWaitForMultipleObjectsEx API to return indicating
    // that messages are ready for processing (Specifically, mouse messages
    // intended for the child window may appear if the child window has
    // capture).
    // The subsequent PeekMessages call may fail to return any messages thus
    // causing us to enter a tight loop at times.
    // The WaitMessage call below is a workaround to give the child window
    // some time to process its input messages.
    MSG msg = {0};
    DWORD queue_status = GetQueueStatus(QS_MOUSE);
    if (HIWORD(queue_status) & QS_MOUSE &&
        !PeekMessage(&msg, NULL, WM_MOUSEFIRST, WM_MOUSELAST, PM_NOREMOVE)) {
      WaitMessage();
    }
    return;
  }

  DCHECK_NE(WAIT_FAILED, result) << GetLastError();
}

void MessagePumpForUI::HandleWorkMessage() {
  // If we are being called outside of the context of Run, then don't try to do
  // any work.  This could correspond to a MessageBox call or something of that
  // sort.
  if (!state_) {
    // Since we handled a kMsgHaveWork message, we must still update this flag.
    InterlockedExchange(&have_work_, 0);
    return;
  }

  // Let whatever would have run had we not been putting messages in the queue
  // run now.  This is an attempt to make our dummy message not starve other
  // messages that may be in the Windows message queue.
  ProcessPumpReplacementMessage();

  // Now give the delegate a chance to do some work.  He'll let us know if he
  // needs to do more work.
  if (state_->delegate->DoWork())
    ScheduleWork();
}

void MessagePumpForUI::HandleTimerMessage() {
  KillTimer(message_hwnd_, reinterpret_cast<UINT_PTR>(this));

  // If we are being called outside of the context of Run, then don't do
  // anything.  This could correspond to a MessageBox call or something of
  // that sort.
  if (!state_)
    return;

  state_->delegate->DoDelayedWork(&delayed_work_time_);
  if (!delayed_work_time_.is_null()) {
    // A bit gratuitous to set delayed_work_time_ again, but oh well.
    ScheduleDelayedWork(delayed_work_time_);
  }
}

bool MessagePumpForUI::ProcessNextWindowsMessage() {
  // If there are sent messages in the queue then PeekMessage internally
  // dispatches the message and returns false. We return true in this
  // case to ensure that the message loop peeks again instead of calling
  // MsgWaitForMultipleObjectsEx again.
  bool sent_messages_in_queue = false;
  DWORD queue_status = GetQueueStatus(QS_SENDMESSAGE);
  if (HIWORD(queue_status) & QS_SENDMESSAGE)
    sent_messages_in_queue = true;

  MSG msg;
  if (PeekMessage(&msg, NULL, 0, 0, PM_REMOVE) != FALSE)
    return ProcessMessageHelper(msg);

  return sent_messages_in_queue;
}

bool MessagePumpForUI::ProcessMessageHelper(const MSG& msg) {
  TRACE_EVENT1("base", "MessagePumpForUI::ProcessMessageHelper",
               "message", msg.message);
  if (WM_QUIT == msg.message) {
    // Repost the QUIT message so that it will be retrieved by the primary
    // GetMessage() loop.
    state_->should_quit = true;
    PostQuitMessage(static_cast<int>(msg.wParam));
    return false;
  }

  // While running our main message pump, we discard kMsgHaveWork messages.
  if (msg.message == kMsgHaveWork && msg.hwnd == message_hwnd_)
    return ProcessPumpReplacementMessage();

  if (CallMsgFilter(const_cast<MSG*>(&msg), kMessageFilterCode))
    return true;

  WillProcessMessage(msg);

  uint32_t action = MessagePumpDispatcher::POST_DISPATCH_PERFORM_DEFAULT;
  if (state_->dispatcher)
    action = state_->dispatcher->Dispatch(msg);
  if (action & MessagePumpDispatcher::POST_DISPATCH_QUIT_LOOP)
    state_->should_quit = true;
  if (action & MessagePumpDispatcher::POST_DISPATCH_PERFORM_DEFAULT) {
    TranslateMessage(&msg);
    DispatchMessage(&msg);
  }

  DidProcessMessage(msg);
  return true;
}

bool MessagePumpForUI::ProcessPumpReplacementMessage() {
  // When we encounter a kMsgHaveWork message, this method is called to peek
  // and process a replacement message, such as a WM_PAINT or WM_TIMER.  The
  // goal is to make the kMsgHaveWork as non-intrusive as possible, even though
  // a continuous stream of such messages are posted.  This method carefully
  // peeks a message while there is no chance for a kMsgHaveWork to be pending,
  // then resets the have_work_ flag (allowing a replacement kMsgHaveWork to
  // possibly be posted), and finally dispatches that peeked replacement.  Note
  // that the re-post of kMsgHaveWork may be asynchronous to this thread!!

  bool have_message = false;
  MSG msg;
  // We should not process all window messages if we are in the context of an
  // OS modal loop, i.e. in the context of a windows API call like MessageBox.
  // This is to ensure that these messages are peeked out by the OS modal loop.
  if (MessageLoop::current()->os_modal_loop()) {
    // We only peek out WM_PAINT and WM_TIMER here for reasons mentioned above.
    have_message = PeekMessage(&msg, NULL, WM_PAINT, WM_PAINT, PM_REMOVE) ||
                   PeekMessage(&msg, NULL, WM_TIMER, WM_TIMER, PM_REMOVE);
  } else {
    have_message = PeekMessage(&msg, NULL, 0, 0, PM_REMOVE) != FALSE;
  }

  DCHECK(!have_message || kMsgHaveWork != msg.message ||
         msg.hwnd != message_hwnd_);

  // Since we discarded a kMsgHaveWork message, we must update the flag.
  int old_have_work = InterlockedExchange(&have_work_, 0);
  DCHECK(old_have_work);

  // We don't need a special time slice if we didn't have_message to process.
  if (!have_message)
    return false;

  // Guarantee we'll get another time slice in the case where we go into native
  // windows code.   This ScheduleWork() may hurt performance a tiny bit when
  // tasks appear very infrequently, but when the event queue is busy, the
  // kMsgHaveWork events get (percentage wise) rarer and rarer.
  ScheduleWork();
  return ProcessMessageHelper(msg);
}

//-----------------------------------------------------------------------------
// MessagePumpForIO public:

MessagePumpForIO::MessagePumpForIO() {
  port_.Set(CreateIoCompletionPort(INVALID_HANDLE_VALUE, NULL, NULL, 1));
  DCHECK(port_.IsValid());
}

void MessagePumpForIO::ScheduleWork() {
  if (InterlockedExchange(&have_work_, 1))
    return;  // Someone else continued the pumping.

  // Make sure the MessagePump does some work for us.
  BOOL ret = PostQueuedCompletionStatus(port_, 0,
                                        reinterpret_cast<ULONG_PTR>(this),
                                        reinterpret_cast<OVERLAPPED*>(this));
  if (ret)
    return;  // Post worked perfectly.

  // See comment in MessagePumpForUI::ScheduleWork() for this error recovery.
  InterlockedExchange(&have_work_, 0);  // Clarify that we didn't succeed.
  UMA_HISTOGRAM_ENUMERATION("Chrome.MessageLoopProblem", COMPLETION_POST_ERROR,
                            MESSAGE_LOOP_PROBLEM_MAX);
}

void MessagePumpForIO::ScheduleDelayedWork(const TimeTicks& delayed_work_time) {
  // We know that we can't be blocked right now since this method can only be
  // called on the same thread as Run, so we only need to update our record of
  // how long to sleep when we do sleep.
  delayed_work_time_ = delayed_work_time;
}

void MessagePumpForIO::RegisterIOHandler(HANDLE file_handle,
                                         IOHandler* handler) {
  ULONG_PTR key = HandlerToKey(handler, true);
  HANDLE port = CreateIoCompletionPort(file_handle, port_, key, 1);
  DPCHECK(port);
}

bool MessagePumpForIO::RegisterJobObject(HANDLE job_handle,
                                         IOHandler* handler) {
  // Job object notifications use the OVERLAPPED pointer to carry the message
  // data. Mark the completion key correspondingly, so we will not try to
  // convert OVERLAPPED* to IOContext*.
  ULONG_PTR key = HandlerToKey(handler, false);
  JOBOBJECT_ASSOCIATE_COMPLETION_PORT info;
  info.CompletionKey = reinterpret_cast<void*>(key);
  info.CompletionPort = port_;
  return SetInformationJobObject(job_handle,
                                 JobObjectAssociateCompletionPortInformation,
                                 &info,
                                 sizeof(info)) != FALSE;
}

//-----------------------------------------------------------------------------
// MessagePumpForIO private:

void MessagePumpForIO::DoRunLoop() {
  for (;;) {
    // If we do any work, we may create more messages etc., and more work may
    // possibly be waiting in another task group.  When we (for example)
    // WaitForIOCompletion(), there is a good chance there are still more
    // messages waiting.  On the other hand, when any of these methods return
    // having done no work, then it is pretty unlikely that calling them
    // again quickly will find any work to do.  Finally, if they all say they
    // had no work, then it is a good time to consider sleeping (waiting) for
    // more work.

    bool more_work_is_plausible = state_->delegate->DoWork();
    if (state_->should_quit)
      break;

    more_work_is_plausible |= WaitForIOCompletion(0, NULL);
    if (state_->should_quit)
      break;

    more_work_is_plausible |=
        state_->delegate->DoDelayedWork(&delayed_work_time_);
    if (state_->should_quit)
      break;

    if (more_work_is_plausible)
      continue;

    more_work_is_plausible = state_->delegate->DoIdleWork();
    if (state_->should_quit)
      break;

    if (more_work_is_plausible)
      continue;

    WaitForWork();  // Wait (sleep) until we have work to do again.
  }
}

// Wait until IO completes, up to the time needed by the timer manager to fire
// the next set of timers.
void MessagePumpForIO::WaitForWork() {
  // We do not support nested IO message loops. This is to avoid messy
  // recursion problems.
  DCHECK_EQ(1, state_->run_depth) << "Cannot nest an IO message loop!";

  int timeout = GetCurrentDelay();
  if (timeout < 0)  // Negative value means no timers waiting.
    timeout = INFINITE;

  WaitForIOCompletion(timeout, NULL);
}

bool MessagePumpForIO::WaitForIOCompletion(DWORD timeout, IOHandler* filter) {
  IOItem item;
  if (completed_io_.empty() || !MatchCompletedIOItem(filter, &item)) {
    // We have to ask the system for another IO completion.
    if (!GetIOItem(timeout, &item))
      return false;

    if (ProcessInternalIOItem(item))
      return true;
  }

  // If |item.has_valid_io_context| is false then |item.context| does not point
  // to a context structure, and so should not be dereferenced, although it may
  // still hold valid non-pointer data.
  if (!item.has_valid_io_context || item.context->handler) {
    if (filter && item.handler != filter) {
      // Save this item for later
      completed_io_.push_back(item);
    } else {
      DCHECK(!item.has_valid_io_context ||
             (item.context->handler == item.handler));
      WillProcessIOEvent();
      item.handler->OnIOCompleted(item.context, item.bytes_transfered,
                                  item.error);
      DidProcessIOEvent();
    }
  } else {
    // The handler must be gone by now, just cleanup the mess.
    delete item.context;
  }
  return true;
}

// Asks the OS for another IO completion result.
bool MessagePumpForIO::GetIOItem(DWORD timeout, IOItem* item) {
  memset(item, 0, sizeof(*item));
  ULONG_PTR key = NULL;
  OVERLAPPED* overlapped = NULL;
  if (!GetQueuedCompletionStatus(port_.Get(), &item->bytes_transfered, &key,
                                 &overlapped, timeout)) {
    if (!overlapped)
      return false;  // Nothing in the queue.
    item->error = GetLastError();
    item->bytes_transfered = 0;
  }

  item->handler = KeyToHandler(key, &item->has_valid_io_context);
  item->context = reinterpret_cast<IOContext*>(overlapped);
  return true;
}

bool MessagePumpForIO::ProcessInternalIOItem(const IOItem& item) {
  if (this == reinterpret_cast<MessagePumpForIO*>(item.context) &&
      this == reinterpret_cast<MessagePumpForIO*>(item.handler)) {
    // This is our internal completion.
    DCHECK(!item.bytes_transfered);
    InterlockedExchange(&have_work_, 0);
    return true;
  }
  return false;
}

// Returns a completion item that was previously received.
bool MessagePumpForIO::MatchCompletedIOItem(IOHandler* filter, IOItem* item) {
  DCHECK(!completed_io_.empty());
  for (std::list<IOItem>::iterator it = completed_io_.begin();
       it != completed_io_.end(); ++it) {
    if (!filter || it->handler == filter) {
      *item = *it;
      completed_io_.erase(it);
      return true;
    }
  }
  return false;
}

void MessagePumpForIO::AddIOObserver(IOObserver *obs) {
  io_observers_.AddObserver(obs);
}

void MessagePumpForIO::RemoveIOObserver(IOObserver *obs) {
  io_observers_.RemoveObserver(obs);
}

void MessagePumpForIO::WillProcessIOEvent() {
  FOR_EACH_OBSERVER(IOObserver, io_observers_, WillProcessIOEvent());
}

void MessagePumpForIO::DidProcessIOEvent() {
  FOR_EACH_OBSERVER(IOObserver, io_observers_, DidProcessIOEvent());
}

// static
ULONG_PTR MessagePumpForIO::HandlerToKey(IOHandler* handler,
                                         bool has_valid_io_context) {
  ULONG_PTR key = reinterpret_cast<ULONG_PTR>(handler);

  // |IOHandler| is at least pointer-size aligned, so the lowest two bits are
  // always cleared. We use the lowest bit to distinguish completion keys with
  // and without the associated |IOContext|.
  DCHECK((key & 1) == 0);

  // Mark the completion key as context-less.
  if (!has_valid_io_context)
    key = key | 1;
  return key;
}

// static
MessagePumpForIO::IOHandler* MessagePumpForIO::KeyToHandler(
    ULONG_PTR key,
    bool* has_valid_io_context) {
  *has_valid_io_context = ((key & 1) == 0);
  return reinterpret_cast<IOHandler*>(key & ~static_cast<ULONG_PTR>(1));
}

}  // namespace base