base/message_loop/message_pump_win.cc

// 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 <stdint.h>

#include <limits>

#include "base/memory/ptr_util.h"
#include "base/message_loop/message_loop.h"
#include "base/metrics/histogram.h"
#include "base/strings/stringprintf.h"
#include "base/trace_event/trace_event.h"
#include "base/win/current_module.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,
};

// The following define pointers to user32 API's for the API's which are used
// in this file. These are added to avoid directly depending on user32 from
// base as there are users of base who don't want this.
decltype(::TranslateMessage)* g_translate_message = nullptr;
decltype(::DispatchMessageW)* g_dispatch_message = nullptr;
decltype(::PeekMessageW)* g_peek_message = nullptr;
decltype(::PostMessageW)* g_post_message = nullptr;
decltype(::DefWindowProcW)* g_def_window_proc = nullptr;
decltype(::PostQuitMessage)* g_post_quit = nullptr;
decltype(::UnregisterClassW)* g_unregister_class = nullptr;
decltype(::RegisterClassExW)* g_register_class = nullptr;
decltype(::CreateWindowExW)* g_create_window_ex = nullptr;
decltype(::DestroyWindow)* g_destroy_window = nullptr;
decltype(::CallMsgFilterW)* g_call_msg_filter = nullptr;
decltype(::GetQueueStatus)* g_get_queue_status = nullptr;
decltype(::MsgWaitForMultipleObjectsEx)* g_msg_wait_for_multiple_objects_ex =
    nullptr;
decltype(::SetTimer)* g_set_timer = nullptr;
decltype(::KillTimer)* g_kill_timer = nullptr;

#define GET_USER32_API(module, name)         \
  reinterpret_cast<decltype(name)*>(::GetProcAddress(module, #name))

// Initializes the global pointers to user32 APIs for the API's used in this
// file.
void InitUser32APIs() {
  if (g_translate_message)
    return;

  HMODULE user32_module = ::GetModuleHandle(L"user32.dll");
  CHECK(user32_module);

  g_translate_message = GET_USER32_API(user32_module, TranslateMessage);
  CHECK(g_translate_message);

  g_dispatch_message = GET_USER32_API(user32_module, DispatchMessageW);
  CHECK(g_dispatch_message);

  g_peek_message = GET_USER32_API(user32_module, PeekMessageW);
  CHECK(g_peek_message);

  g_post_message = GET_USER32_API(user32_module, PostMessageW);
  CHECK(g_post_message);

  g_def_window_proc = GET_USER32_API(user32_module, DefWindowProcW);
  CHECK(g_def_window_proc);

  g_post_quit = GET_USER32_API(user32_module, PostQuitMessage);
  CHECK(g_post_quit);

  g_unregister_class = GET_USER32_API(user32_module, UnregisterClassW);
  CHECK(g_unregister_class);

  g_register_class = GET_USER32_API(user32_module, RegisterClassExW);
  CHECK(g_register_class);

  g_create_window_ex = GET_USER32_API(user32_module, CreateWindowExW);
  CHECK(g_create_window_ex);

  g_destroy_window = GET_USER32_API(user32_module, DestroyWindow);
  CHECK(g_destroy_window);

  g_call_msg_filter = GET_USER32_API(user32_module, CallMsgFilterW);
  CHECK(g_call_msg_filter);

  g_get_queue_status = GET_USER32_API(user32_module, GetQueueStatus);
  CHECK(g_get_queue_status);

  g_msg_wait_for_multiple_objects_ex =
      GET_USER32_API(user32_module, MsgWaitForMultipleObjectsEx);
  CHECK(g_msg_wait_for_multiple_objects_ex);

  g_set_timer = GET_USER32_API(user32_module, SetTimer);
  CHECK(g_set_timer);

  g_kill_timer = GET_USER32_API(user32_module, KillTimer);
  CHECK(g_kill_timer);
}

}  // 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;

// The application-defined code passed to the hook procedure.
static const int kMessageFilterCode = 0x5001;

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

MessagePumpWin::MessagePumpWin() {
}

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

  // TODO(stanisc): crbug.com/596190: Remove this code once the bug is fixed.
  s.schedule_work_error_count = 0;
  s.last_schedule_work_error_time = Time();

  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());

  // Range check the |timeout| while converting to an integer.  If the |timeout|
  // is negative, then we need to run delayed work soon.  If the |timeout| is
  // "overflowingly" large, that means a delayed task was posted with a
  // super-long delay.
  return timeout < 0 ? 0 :
      (timeout > std::numeric_limits<int>::max() ?
       std::numeric_limits<int>::max() : static_cast<int>(timeout));
}

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

MessagePumpForUI::MessagePumpForUI()
    : atom_(0) {
  InitUser32APIs();
  InitMessageWnd();
}

MessagePumpForUI::~MessagePumpForUI() {
  g_destroy_window(message_hwnd_);
  g_unregister_class(MAKEINTATOM(atom_), CURRENT_MODULE());
}

void MessagePumpForUI::ScheduleWork() {
  if (InterlockedExchange(&work_state_, HAVE_WORK) != READY)
    return;  // Someone else continued the pumping.

  // Make sure the MessagePump does some work for us.
  BOOL ret = g_post_message(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.

  // Clarify that we didn't really insert.
  InterlockedExchange(&work_state_, READY);
  UMA_HISTOGRAM_ENUMERATION("Chrome.MessageLoopProblem", MESSAGE_POST_ERROR,
                            MESSAGE_LOOP_PROBLEM_MAX);
  state_->schedule_work_error_count++;
  state_->last_schedule_work_error_time = Time::Now();
}

void MessagePumpForUI::ScheduleDelayedWork(const TimeTicks& delayed_work_time) {
  delayed_work_time_ = delayed_work_time;
  RescheduleTimer();
}

//-----------------------------------------------------------------------------
// 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 g_def_window_proc(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())
      g_kill_timer(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 = CURRENT_MODULE();
  WNDCLASSEX wc = {0};
  wc.cbSize = sizeof(wc);
  wc.lpfnWndProc = base::win::WrappedWindowProc<WndProcThunk>;
  wc.hInstance = instance;
  wc.lpszClassName = class_name.c_str();
  atom_ = g_register_class(&wc);
  DCHECK(atom_);

  message_hwnd_ = g_create_window_ex(0, 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;
  DWORD wait_flags = MWMO_INPUTAVAILABLE;

  while ((delay = GetCurrentDelay()) != 0) {
    if (delay < 0)  // Negative value means no timers waiting.
      delay = INFINITE;

    DWORD result = g_msg_wait_for_multiple_objects_ex(0, nullptr, delay,
                                                      QS_ALLINPUT, wait_flags);

    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 code below is a workaround to give the child window
      // some time to process its input messages by looping back to
      // MsgWaitForMultipleObjectsEx above when there are no messages for the
      // current thread.
      MSG msg = {0};
      bool has_pending_sent_message =
          (HIWORD(g_get_queue_status(QS_SENDMESSAGE)) & QS_SENDMESSAGE) != 0;
      if (has_pending_sent_message ||
          g_peek_message(&msg, nullptr, 0, 0, PM_NOREMOVE)) {
        return;
      }

      // We know there are no more messages for this thread because PeekMessage
      // has returned false. Reset |wait_flags| so that we wait for a *new*
      // message.
      wait_flags = 0;
    }

    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(&work_state_, READY);
    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.  It'll let us know if it
  // needs to do more work.
  if (state_->delegate->DoWork())
    ScheduleWork();
  state_->delegate->DoDelayedWork(&delayed_work_time_);
  RescheduleTimer();
}

void MessagePumpForUI::HandleTimerMessage() {
  g_kill_timer(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_);
  RescheduleTimer();
}

void MessagePumpForUI::RescheduleTimer() {
  if (delayed_work_time_.is_null())
    return;
  //
  // 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 spurious SetTimer event firing is benign, as we'll just be
  // processing an empty timer queue.
  //
  int delay_msec = GetCurrentDelay();
  DCHECK_GE(delay_msec, 0);
  if (delay_msec == 0) {
    ScheduleWork();
  } else {
    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 = g_set_timer(message_hwnd_, reinterpret_cast<UINT_PTR>(this),
                           delay_msec, nullptr);
    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);
  }
}

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 = g_get_queue_status(QS_SENDMESSAGE);
  if (HIWORD(queue_status) & QS_SENDMESSAGE)
    sent_messages_in_queue = true;

  MSG msg;
  if (g_peek_message(&msg, nullptr, 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;
    g_post_quit(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 (g_call_msg_filter(const_cast<MSG*>(&msg), kMessageFilterCode))
    return true;

  g_translate_message(&msg);
  g_dispatch_message(&msg);

  return true;
}

bool MessagePumpForUI::ProcessPumpReplacementMessage() {
  // When we encounter a kMsgHaveWork message, this method is called to peek and
  // process a replacement message. 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!!

  MSG msg;
  const bool have_message =
      g_peek_message(&msg, nullptr, 0, 0, PM_REMOVE) != FALSE;

  // Expect no message or a message different than kMsgHaveWork.
  DCHECK(!have_message || kMsgHaveWork != msg.message ||
         msg.hwnd != message_hwnd_);

  // Since we discarded a kMsgHaveWork message, we must update the flag.
  int old_work_state_ = InterlockedExchange(&work_state_, READY);
  DCHECK_EQ(HAVE_WORK, old_work_state_);

  // 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);
}

//-----------------------------------------------------------------------------
// MessagePumpForGpu public:

MessagePumpForGpu::MessagePumpForGpu() {
  event_.Set(CreateEvent(nullptr, FALSE, FALSE, nullptr));
  InitUser32APIs();
}

MessagePumpForGpu::~MessagePumpForGpu() {}

// static
void MessagePumpForGpu::InitFactory() {
  bool init_result = MessageLoop::InitMessagePumpForUIFactory(
      &MessagePumpForGpu::CreateMessagePumpForGpu);
  DCHECK(init_result);
}

// static
std::unique_ptr<MessagePump> MessagePumpForGpu::CreateMessagePumpForGpu() {
  return WrapUnique<MessagePump>(new MessagePumpForGpu);
}

void MessagePumpForGpu::ScheduleWork() {
  if (InterlockedExchange(&work_state_, HAVE_WORK) != READY)
    return;  // Someone else continued the pumping.

  // TODO(stanisc): crbug.com/596190: Preserve for crash dump analysis.
  // Remove this when the bug is fixed.
  last_set_event_timeticks_ = TimeTicks::Now();

  // Make sure the MessagePump does some work for us.
  SetEvent(event_.Get());
}

void MessagePumpForGpu::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;
}

bool MessagePumpForGpu::WasSignaled() {
  // If |event_| was set this would reset it back to unset state.
  return WaitForSingleObject(event_.Get(), 0) == WAIT_OBJECT_0;
}

//-----------------------------------------------------------------------------
// MessagePumpForGpu private:

void MessagePumpForGpu::DoRunLoop() {
  while (!state_->should_quit) {
    // Indicate that the loop is handling the work.
    // If there is a race condition between switching to WORKING state here and
    // the producer thread setting the HAVE_WORK state after exiting the wait,
    // the event might remain in the signalled state. That might be less than
    // optimal but wouldn't result in failing to handle the work.
    InterlockedExchange(&work_state_, WORKING);

    bool more_work_is_plausible = ProcessNextMessage();
    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 (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;

    // Switch that working state to READY to indicate that the loop is
    // waiting for accepting new work if it is still in WORKING state and hasn't
    // been signalled. Otherwise if it is in HAVE_WORK state skip the wait
    // and proceed to handing the work.
    if (InterlockedCompareExchange(&work_state_, READY, WORKING) == HAVE_WORK)
      continue;  // Skip wait, more work was requested.

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

void MessagePumpForGpu::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;

  // The while loop handles the situation where on Windows 7 and later versions
  // MsgWaitForMultipleObjectsEx might time out slightly earlier (less than one
  // ms) than the specified |delay|. In that situation it is more optimal to
  // just wait again rather than waste a DoRunLoop cycle.
  while ((delay = GetCurrentDelay()) != 0) {
    if (delay < 0)  // Negative value means no timers waiting.
      delay = INFINITE;

    // TODO(stanisc): crbug.com/596190: Preserve for crash dump analysis.
    // Remove this when the bug is fixed.
    TimeTicks wait_for_work_timeticks = TimeTicks::Now();
    debug::Alias(&wait_for_work_timeticks);
    debug::Alias(&delay);

    HANDLE handle = event_.Get();
    DWORD result =
        g_msg_wait_for_multiple_objects_ex(1, &handle, delay, QS_ALLINPUT, 0);
    DCHECK_NE(WAIT_FAILED, result) << GetLastError();
    if (result != WAIT_TIMEOUT) {
      // Either work or message available.
      return;
    }
  }
}

bool MessagePumpForGpu::ProcessNextMessage() {
  MSG msg;
  if (!g_peek_message(&msg, nullptr, 0, 0, PM_REMOVE))
    return false;

  if (msg.message == WM_QUIT) {
    // Repost the QUIT message so that it will be retrieved by the primary
    // GetMessage() loop.
    state_->should_quit = true;
    g_post_quit(static_cast<int>(msg.wParam));
    return false;
  }

  if (!g_call_msg_filter(const_cast<MSG*>(&msg), kMessageFilterCode)) {
    g_translate_message(&msg);
    g_dispatch_message(&msg);
  }

  return true;
}

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

MessagePumpForIO::IOContext::IOContext() {
  memset(&overlapped, 0, sizeof(overlapped));
}

MessagePumpForIO::MessagePumpForIO() {
  port_.Set(CreateIoCompletionPort(INVALID_HANDLE_VALUE, nullptr,
      reinterpret_cast<ULONG_PTR>(nullptr), 1));
  DCHECK(port_.IsValid());
}

MessagePumpForIO::~MessagePumpForIO() = default;

void MessagePumpForIO::ScheduleWork() {
  if (InterlockedExchange(&work_state_, HAVE_WORK) != READY)
    return;  // Someone else continued the pumping.

  // Make sure the MessagePump does some work for us.
  BOOL ret = PostQueuedCompletionStatus(port_.Get(), 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(&work_state_, READY);  // Clarify that we didn't succeed.
  UMA_HISTOGRAM_ENUMERATION("Chrome.MessageLoopProblem", COMPLETION_POST_ERROR,
                            MESSAGE_LOOP_PROBLEM_MAX);
  state_->schedule_work_error_count++;
  state_->last_schedule_work_error_time = Time::Now();
}

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) {
  HANDLE port = CreateIoCompletionPort(file_handle, port_.Get(),
                                       reinterpret_cast<ULONG_PTR>(handler), 1);
  DPCHECK(port);
}

bool MessagePumpForIO::RegisterJobObject(HANDLE job_handle,
                                         IOHandler* handler) {
  JOBOBJECT_ASSOCIATE_COMPLETION_PORT info;
  info.CompletionKey = handler;
  info.CompletionPort = port_.Get();
  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, nullptr);
    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, nullptr);
}

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 (filter && item.handler != filter) {
    // Save this item for later
    completed_io_.push_back(item);
  } else {
    item.handler->OnIOCompleted(item.context, item.bytes_transfered,
                                item.error);
  }
  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 = reinterpret_cast<ULONG_PTR>(nullptr);
  OVERLAPPED* overlapped = nullptr;
  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 = reinterpret_cast<IOHandler*>(key);
  item->context = reinterpret_cast<IOContext*>(overlapped);
  return true;
}

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

}  // namespace base