src/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 <limits>

#include "base/debug/alias.h"
#include "base/memory/ptr_util.h"
#include "base/metrics/histogram_macros.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"
#include "starboard/memory.h"
#include "starboard/types.h"

namespace base {

namespace {

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

}  // namespace

// 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:

MessagePumpWin::MessagePumpWin() = default;

void MessagePumpWin::Run(Delegate* delegate) {
  RunState s;
  s.delegate = delegate;
  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());

  // 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() {
  bool succeeded = message_window_.Create(
      BindRepeating(&MessagePumpForUI::MessageCallback, Unretained(this)));
  DCHECK(succeeded);
}

MessagePumpForUI::~MessagePumpForUI() = default;

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 = PostMessage(message_window_.hwnd(), kMsgHaveWork, 0, 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 run 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);
}

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

void MessagePumpForUI::EnableWmQuit() {
  enable_wm_quit_ = true;
}

void MessagePumpForUI::AddObserver(Observer* observer) {
  observers_.AddObserver(observer);
}

void MessagePumpForUI::RemoveObserver(Observer* observer) {
  observers_.RemoveObserver(observer);
}

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

bool MessagePumpForUI::MessageCallback(
    UINT message, WPARAM wparam, LPARAM lparam, LRESULT* result) {
  switch (message) {
    case kMsgHaveWork:
      HandleWorkMessage();
      break;
    case WM_TIMER:
      HandleTimerMessage();
      break;
  }
  return false;
}

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_window_.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::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;

    // Tell the optimizer to retain these values to simplify analyzing hangs.
    base::debug::Alias(&delay);
    base::debug::Alias(&wait_flags);
    DWORD result = MsgWaitForMultipleObjectsEx(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(::GetQueueStatus(QS_SENDMESSAGE)) & QS_SENDMESSAGE) != 0;
      if (has_pending_sent_message ||
          ::PeekMessage(&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() {
  KillTimer(message_window_.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;

    // Tell the optimizer to retain these values to simplify analyzing hangs.
    base::debug::Alias(&delay_msec);
    // 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).
    UINT_PTR ret = SetTimer(message_window_.hwnd(), 0, 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 = ::GetQueueStatus(QS_SENDMESSAGE);
  if (HIWORD(queue_status) & QS_SENDMESSAGE)
    sent_messages_in_queue = true;

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

  return sent_messages_in_queue;
}

bool MessagePumpForUI::ProcessMessageHelper(const MSG& msg) {
  TRACE_EVENT1("base,toplevel", "MessagePumpForUI::ProcessMessageHelper",
               "message", msg.message);
  if (WM_QUIT == msg.message) {
    // WM_QUIT is the standard way to exit a ::GetMessage() loop. Our
    // MessageLoop has its own quit mechanism, so WM_QUIT should only terminate
    // it if |enable_wm_quit_| is explicitly set (and is generally unexpected
    // otherwise).
    if (enable_wm_quit_) {
      state_->should_quit = true;
      return false;
    }
    UMA_HISTOGRAM_ENUMERATION("Chrome.MessageLoopProblem",
                              RECEIVED_WM_QUIT_ERROR, MESSAGE_LOOP_PROBLEM_MAX);
    return true;
  }

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

  for (Observer& observer : observers_)
    observer.WillDispatchMSG(msg);
  ::TranslateMessage(&msg);
  ::DispatchMessage(&msg);
  for (Observer& observer : observers_)
    observer.DidDispatchMSG(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 =
      ::PeekMessage(&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_window_.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;

  if (WM_QUIT == msg.message) {
    // If we're in a nested ::GetMessage() loop then we must let that loop see
    // the WM_QUIT in order for it to exit. If we're in DoRunLoop then the re-
    // posted WM_QUIT will be either ignored, or handled, by
    // ProcessMessageHelper() called directly from ProcessNextWindowsMessage().
    ::PostQuitMessage(static_cast<int>(msg.wParam));
    // Note: we *must not* ScheduleWork() here as WM_QUIT is a low-priority
    // message on Windows (it is only returned by ::PeekMessage() when idle) :
    // https://blogs.msdn.microsoft.com/oldnewthing/20051104-33/?p=33453. As
    // such posting a kMsgHaveWork message via ScheduleWork() would cause an
    // infinite loop (kMsgHaveWork message handled first means we end up here
    // again and repost WM_QUIT+ScheduleWork() again, etc.). Not leaving a
    // kMsgHaveWork message behind however is also problematic as unwinding
    // multiple layers of nested ::GetMessage() loops can result in starving
    // application tasks. TODO(https://crbug.com/890016) : Fix this.

    // The return value is mostly irrelevant but return true like we would after
    // processing a QuitClosure() task.
    return true;
  }

  // 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::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);
}

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;
}

HRESULT MessagePumpForIO::RegisterIOHandler(HANDLE file_handle,
                                            IOHandler* handler) {
  HANDLE port = CreateIoCompletionPort(file_handle, port_.Get(),
                                       reinterpret_cast<ULONG_PTR>(handler), 1);
  return (port != nullptr) ? S_OK : HRESULT_FROM_WIN32(GetLastError());
}

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;

  // Tell the optimizer to retain these values to simplify analyzing hangs.
  base::debug::Alias(&timeout);
  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