michael@0: // Copyright (c) 2009 The Chromium Authors. All rights reserved.
michael@0: // Use of this source code is governed by a BSD-style license that can be
michael@0: // found in the LICENSE file.
michael@0: 
michael@0: #include "base/message_pump_win.h"
michael@0: 
michael@0: #include <math.h>
michael@0: 
michael@0: #include "base/message_loop.h"
michael@0: #include "base/histogram.h"
michael@0: #include "base/win_util.h"
michael@0: 
michael@0: using base::Time;
michael@0: 
michael@0: namespace base {
michael@0: 
michael@0: static const wchar_t kWndClass[] = L"Chrome_MessagePumpWindow";
michael@0: 
michael@0: // Message sent to get an additional time slice for pumping (processing) another
michael@0: // task (a series of such messages creates a continuous task pump).
michael@0: static const int kMsgHaveWork = WM_USER + 1;
michael@0: 
michael@0: //-----------------------------------------------------------------------------
michael@0: // MessagePumpWin public:
michael@0: 
michael@0: void MessagePumpWin::AddObserver(Observer* observer) {
michael@0:   observers_.AddObserver(observer);
michael@0: }
michael@0: 
michael@0: void MessagePumpWin::RemoveObserver(Observer* observer) {
michael@0:   observers_.RemoveObserver(observer);
michael@0: }
michael@0: 
michael@0: void MessagePumpWin::WillProcessMessage(const MSG& msg) {
michael@0:   FOR_EACH_OBSERVER(Observer, observers_, WillProcessMessage(msg));
michael@0: }
michael@0: 
michael@0: void MessagePumpWin::DidProcessMessage(const MSG& msg) {
michael@0:   FOR_EACH_OBSERVER(Observer, observers_, DidProcessMessage(msg));
michael@0: }
michael@0: 
michael@0: void MessagePumpWin::RunWithDispatcher(
michael@0:     Delegate* delegate, Dispatcher* dispatcher) {
michael@0:   RunState s;
michael@0:   s.delegate = delegate;
michael@0:   s.dispatcher = dispatcher;
michael@0:   s.should_quit = false;
michael@0:   s.run_depth = state_ ? state_->run_depth + 1 : 1;
michael@0: 
michael@0:   RunState* previous_state = state_;
michael@0:   state_ = &s;
michael@0: 
michael@0:   DoRunLoop();
michael@0: 
michael@0:   state_ = previous_state;
michael@0: }
michael@0: 
michael@0: void MessagePumpWin::Quit() {
michael@0:   DCHECK(state_);
michael@0:   state_->should_quit = true;
michael@0: }
michael@0: 
michael@0: //-----------------------------------------------------------------------------
michael@0: // MessagePumpWin protected:
michael@0: 
michael@0: int MessagePumpWin::GetCurrentDelay() const {
michael@0:   if (delayed_work_time_.is_null())
michael@0:     return -1;
michael@0: 
michael@0:   // Be careful here.  TimeDelta has a precision of microseconds, but we want a
michael@0:   // value in milliseconds.  If there are 5.5ms left, should the delay be 5 or
michael@0:   // 6?  It should be 6 to avoid executing delayed work too early.
michael@0:   double timeout =
michael@0:       ceil((delayed_work_time_ - TimeTicks::Now()).InMillisecondsF());
michael@0: 
michael@0:   // If this value is negative, then we need to run delayed work soon.
michael@0:   int delay = static_cast<int>(timeout);
michael@0:   if (delay < 0)
michael@0:     delay = 0;
michael@0: 
michael@0:   return delay;
michael@0: }
michael@0: 
michael@0: //-----------------------------------------------------------------------------
michael@0: // MessagePumpForUI public:
michael@0: 
michael@0: MessagePumpForUI::MessagePumpForUI() {
michael@0:   InitMessageWnd();
michael@0: }
michael@0: 
michael@0: MessagePumpForUI::~MessagePumpForUI() {
michael@0:   DestroyWindow(message_hwnd_);
michael@0:   UnregisterClass(kWndClass, GetModuleHandle(NULL));
michael@0: }
michael@0: 
michael@0: void MessagePumpForUI::ScheduleWork() {
michael@0:   if (InterlockedExchange(&have_work_, 1))
michael@0:     return;  // Someone else continued the pumping.
michael@0: 
michael@0:   // Make sure the MessagePump does some work for us.
michael@0:   PostMessage(message_hwnd_, kMsgHaveWork, reinterpret_cast<WPARAM>(this), 0);
michael@0: 
michael@0:   // In order to wake up any cross-process COM calls which may currently be
michael@0:   // pending on the main thread, we also have to post a UI message.
michael@0:   PostMessage(message_hwnd_, WM_NULL, 0, 0);
michael@0: }
michael@0: 
michael@0: void MessagePumpForUI::ScheduleDelayedWork(const TimeTicks& delayed_work_time) {
michael@0:   //
michael@0:   // We would *like* to provide high resolution timers.  Windows timers using
michael@0:   // SetTimer() have a 10ms granularity.  We have to use WM_TIMER as a wakeup
michael@0:   // mechanism because the application can enter modal windows loops where it
michael@0:   // is not running our MessageLoop; the only way to have our timers fire in
michael@0:   // these cases is to post messages there.
michael@0:   //
michael@0:   // To provide sub-10ms timers, we process timers directly from our run loop.
michael@0:   // For the common case, timers will be processed there as the run loop does
michael@0:   // its normal work.  However, we *also* set the system timer so that WM_TIMER
michael@0:   // events fire.  This mops up the case of timers not being able to work in
michael@0:   // modal message loops.  It is possible for the SetTimer to pop and have no
michael@0:   // pending timers, because they could have already been processed by the
michael@0:   // run loop itself.
michael@0:   //
michael@0:   // We use a single SetTimer corresponding to the timer that will expire
michael@0:   // soonest.  As new timers are created and destroyed, we update SetTimer.
michael@0:   // Getting a spurrious SetTimer event firing is benign, as we'll just be
michael@0:   // processing an empty timer queue.
michael@0:   //
michael@0:   delayed_work_time_ = delayed_work_time;
michael@0: 
michael@0:   int delay_msec = GetCurrentDelay();
michael@0:   DCHECK(delay_msec >= 0);
michael@0:   if (delay_msec < USER_TIMER_MINIMUM)
michael@0:     delay_msec = USER_TIMER_MINIMUM;
michael@0: 
michael@0:   // Create a WM_TIMER event that will wake us up to check for any pending
michael@0:   // timers (in case we are running within a nested, external sub-pump).
michael@0:   SetTimer(message_hwnd_, reinterpret_cast<UINT_PTR>(this), delay_msec, NULL);
michael@0: }
michael@0: 
michael@0: void MessagePumpForUI::PumpOutPendingPaintMessages() {
michael@0:   // If we are being called outside of the context of Run, then don't try to do
michael@0:   // any work.
michael@0:   if (!state_)
michael@0:     return;
michael@0: 
michael@0:   // Create a mini-message-pump to force immediate processing of only Windows
michael@0:   // WM_PAINT messages.  Don't provide an infinite loop, but do enough peeking
michael@0:   // to get the job done.  Actual common max is 4 peeks, but we'll be a little
michael@0:   // safe here.
michael@0:   const int kMaxPeekCount = 20;
michael@0:   bool win2k = win_util::GetWinVersion() <= win_util::WINVERSION_2000;
michael@0:   int peek_count;
michael@0:   for (peek_count = 0; peek_count < kMaxPeekCount; ++peek_count) {
michael@0:     MSG msg;
michael@0:     if (win2k) {
michael@0:       if (!PeekMessage(&msg, NULL, WM_PAINT, WM_PAINT, PM_REMOVE))
michael@0:         break;
michael@0:     } else {
michael@0:       if (!PeekMessage(&msg, NULL, 0, 0, PM_REMOVE | PM_QS_PAINT))
michael@0:         break;
michael@0:     }
michael@0:     ProcessMessageHelper(msg);
michael@0:     if (state_->should_quit)  // Handle WM_QUIT.
michael@0:       break;
michael@0:   }
michael@0:   // Histogram what was really being used, to help to adjust kMaxPeekCount.
michael@0:   DHISTOGRAM_COUNTS("Loop.PumpOutPendingPaintMessages Peeks", peek_count);
michael@0: }
michael@0: 
michael@0: //-----------------------------------------------------------------------------
michael@0: // MessagePumpForUI private:
michael@0: 
michael@0: // static
michael@0: LRESULT CALLBACK MessagePumpForUI::WndProcThunk(
michael@0:     HWND hwnd, UINT message, WPARAM wparam, LPARAM lparam) {
michael@0:   switch (message) {
michael@0:     case kMsgHaveWork:
michael@0:       reinterpret_cast<MessagePumpForUI*>(wparam)->HandleWorkMessage();
michael@0:       break;
michael@0:     case WM_TIMER:
michael@0:       reinterpret_cast<MessagePumpForUI*>(wparam)->HandleTimerMessage();
michael@0:       break;
michael@0:   }
michael@0:   return DefWindowProc(hwnd, message, wparam, lparam);
michael@0: }
michael@0: 
michael@0: void MessagePumpForUI::DoRunLoop() {
michael@0:   // IF this was just a simple PeekMessage() loop (servicing all possible work
michael@0:   // queues), then Windows would try to achieve the following order according
michael@0:   // to MSDN documentation about PeekMessage with no filter):
michael@0:   //    * Sent messages
michael@0:   //    * Posted messages
michael@0:   //    * Sent messages (again)
michael@0:   //    * WM_PAINT messages
michael@0:   //    * WM_TIMER messages
michael@0:   //
michael@0:   // Summary: none of the above classes is starved, and sent messages has twice
michael@0:   // the chance of being processed (i.e., reduced service time).
michael@0: 
michael@0:   for (;;) {
michael@0:     // If we do any work, we may create more messages etc., and more work may
michael@0:     // possibly be waiting in another task group.  When we (for example)
michael@0:     // ProcessNextWindowsMessage(), there is a good chance there are still more
michael@0:     // messages waiting.  On the other hand, when any of these methods return
michael@0:     // having done no work, then it is pretty unlikely that calling them again
michael@0:     // quickly will find any work to do.  Finally, if they all say they had no
michael@0:     // work, then it is a good time to consider sleeping (waiting) for more
michael@0:     // work.
michael@0: 
michael@0:     bool more_work_is_plausible = ProcessNextWindowsMessage();
michael@0:     if (state_->should_quit)
michael@0:       break;
michael@0: 
michael@0:     more_work_is_plausible |= state_->delegate->DoWork();
michael@0:     if (state_->should_quit)
michael@0:       break;
michael@0: 
michael@0:     more_work_is_plausible |=
michael@0:         state_->delegate->DoDelayedWork(&delayed_work_time_);
michael@0:     // If we did not process any delayed work, then we can assume that our
michael@0:     // existing WM_TIMER if any will fire when delayed work should run.  We
michael@0:     // don't want to disturb that timer if it is already in flight.  However,
michael@0:     // if we did do all remaining delayed work, then lets kill the WM_TIMER.
michael@0:     if (more_work_is_plausible && delayed_work_time_.is_null())
michael@0:       KillTimer(message_hwnd_, reinterpret_cast<UINT_PTR>(this));
michael@0:     if (state_->should_quit)
michael@0:       break;
michael@0: 
michael@0:     if (more_work_is_plausible)
michael@0:       continue;
michael@0: 
michael@0:     more_work_is_plausible = state_->delegate->DoIdleWork();
michael@0:     if (state_->should_quit)
michael@0:       break;
michael@0: 
michael@0:     if (more_work_is_plausible)
michael@0:       continue;
michael@0: 
michael@0:     WaitForWork();  // Wait (sleep) until we have work to do again.
michael@0:   }
michael@0: }
michael@0: 
michael@0: void MessagePumpForUI::InitMessageWnd() {
michael@0:   HINSTANCE hinst = GetModuleHandle(NULL);
michael@0: 
michael@0:   WNDCLASSEX wc = {0};
michael@0:   wc.cbSize = sizeof(wc);
michael@0:   wc.lpfnWndProc = WndProcThunk;
michael@0:   wc.hInstance = hinst;
michael@0:   wc.lpszClassName = kWndClass;
michael@0:   RegisterClassEx(&wc);
michael@0: 
michael@0:   message_hwnd_ =
michael@0:       CreateWindow(kWndClass, 0, 0, 0, 0, 0, 0, HWND_MESSAGE, 0, hinst, 0);
michael@0:   DCHECK(message_hwnd_);
michael@0: }
michael@0: 
michael@0: void MessagePumpForUI::WaitForWork() {
michael@0:   // Wait until a message is available, up to the time needed by the timer
michael@0:   // manager to fire the next set of timers.
michael@0:   int delay = GetCurrentDelay();
michael@0:   if (delay < 0)  // Negative value means no timers waiting.
michael@0:     delay = INFINITE;
michael@0: 
michael@0:   DWORD result;
michael@0:   result = MsgWaitForMultipleObjectsEx(0, NULL, delay, QS_ALLINPUT,
michael@0:                                        MWMO_INPUTAVAILABLE);
michael@0: 
michael@0:   if (WAIT_OBJECT_0 == result) {
michael@0:     // A WM_* message is available.
michael@0:     // If a parent child relationship exists between windows across threads
michael@0:     // then their thread inputs are implicitly attached.
michael@0:     // This causes the MsgWaitForMultipleObjectsEx API to return indicating
michael@0:     // that messages are ready for processing (specifically mouse messages
michael@0:     // intended for the child window. Occurs if the child window has capture)
michael@0:     // The subsequent PeekMessages call fails to return any messages thus
michael@0:     // causing us to enter a tight loop at times.
michael@0:     // The WaitMessage call below is a workaround to give the child window
michael@0:     // sometime to process its input messages.
michael@0:     MSG msg = {0};
michael@0:     DWORD queue_status = GetQueueStatus(QS_MOUSE);
michael@0:     if (HIWORD(queue_status) & QS_MOUSE &&
michael@0:        !PeekMessage(&msg, NULL, WM_MOUSEFIRST, WM_MOUSELAST, PM_NOREMOVE)) {
michael@0:       WaitMessage();
michael@0:     }
michael@0:     return;
michael@0:   }
michael@0: 
michael@0:   DCHECK_NE(WAIT_FAILED, result) << GetLastError();
michael@0: }
michael@0: 
michael@0: void MessagePumpForUI::HandleWorkMessage() {
michael@0:   // If we are being called outside of the context of Run, then don't try to do
michael@0:   // any work.  This could correspond to a MessageBox call or something of that
michael@0:   // sort.
michael@0:   if (!state_) {
michael@0:     // Since we handled a kMsgHaveWork message, we must still update this flag.
michael@0:     InterlockedExchange(&have_work_, 0);
michael@0:     return;
michael@0:   }
michael@0: 
michael@0:   // Let whatever would have run had we not been putting messages in the queue
michael@0:   // run now.  This is an attempt to make our dummy message not starve other
michael@0:   // messages that may be in the Windows message queue.
michael@0:   ProcessPumpReplacementMessage();
michael@0: 
michael@0:   // Now give the delegate a chance to do some work.  He'll let us know if he
michael@0:   // needs to do more work.
michael@0:   if (state_->delegate->DoWork())
michael@0:     ScheduleWork();
michael@0: }
michael@0: 
michael@0: void MessagePumpForUI::HandleTimerMessage() {
michael@0:   KillTimer(message_hwnd_, reinterpret_cast<UINT_PTR>(this));
michael@0: 
michael@0:   // If we are being called outside of the context of Run, then don't do
michael@0:   // anything.  This could correspond to a MessageBox call or something of
michael@0:   // that sort.
michael@0:   if (!state_)
michael@0:     return;
michael@0: 
michael@0:   state_->delegate->DoDelayedWork(&delayed_work_time_);
michael@0:   if (!delayed_work_time_.is_null()) {
michael@0:     // A bit gratuitous to set delayed_work_time_ again, but oh well.
michael@0:     ScheduleDelayedWork(delayed_work_time_);
michael@0:   }
michael@0: }
michael@0: 
michael@0: bool MessagePumpForUI::ProcessNextWindowsMessage() {
michael@0:   // If there are sent messages in the queue then PeekMessage internally
michael@0:   // dispatches the message and returns false. We return true in this
michael@0:   // case to ensure that the message loop peeks again instead of calling
michael@0:   // MsgWaitForMultipleObjectsEx again.
michael@0:   bool sent_messages_in_queue = false;
michael@0:   DWORD queue_status = GetQueueStatus(QS_SENDMESSAGE);
michael@0:   if (HIWORD(queue_status) & QS_SENDMESSAGE)
michael@0:     sent_messages_in_queue = true;
michael@0: 
michael@0:   MSG msg;
michael@0:   if (PeekMessage(&msg, NULL, 0, 0, PM_REMOVE))
michael@0:     return ProcessMessageHelper(msg);
michael@0: 
michael@0:   return sent_messages_in_queue;
michael@0: }
michael@0: 
michael@0: bool MessagePumpForUI::ProcessMessageHelper(const MSG& msg) {
michael@0:   if (WM_QUIT == msg.message) {
michael@0:     // Repost the QUIT message so that it will be retrieved by the primary
michael@0:     // GetMessage() loop.
michael@0:     state_->should_quit = true;
michael@0:     PostQuitMessage(static_cast<int>(msg.wParam));
michael@0:     return false;
michael@0:   }
michael@0: 
michael@0:   // While running our main message pump, we discard kMsgHaveWork messages.
michael@0:   if (msg.message == kMsgHaveWork && msg.hwnd == message_hwnd_)
michael@0:     return ProcessPumpReplacementMessage();
michael@0: 
michael@0:   WillProcessMessage(msg);
michael@0: 
michael@0:   if (state_->dispatcher) {
michael@0:     if (!state_->dispatcher->Dispatch(msg))
michael@0:       state_->should_quit = true;
michael@0:   } else {
michael@0:     TranslateMessage(&msg);
michael@0:     DispatchMessage(&msg);
michael@0:   }
michael@0: 
michael@0:   DidProcessMessage(msg);
michael@0:   return true;
michael@0: }
michael@0: 
michael@0: bool MessagePumpForUI::ProcessPumpReplacementMessage() {
michael@0:   // When we encounter a kMsgHaveWork message, this method is called to peek
michael@0:   // and process a replacement message, such as a WM_PAINT or WM_TIMER.  The
michael@0:   // goal is to make the kMsgHaveWork as non-intrusive as possible, even though
michael@0:   // a continuous stream of such messages are posted.  This method carefully
michael@0:   // peeks a message while there is no chance for a kMsgHaveWork to be pending,
michael@0:   // then resets the have_work_ flag (allowing a replacement kMsgHaveWork to
michael@0:   // possibly be posted), and finally dispatches that peeked replacement.  Note
michael@0:   // that the re-post of kMsgHaveWork may be asynchronous to this thread!!
michael@0: 
michael@0:   MSG msg;
michael@0:   bool have_message = false;
michael@0:   if (MessageLoop::current()->os_modal_loop()) {
michael@0:     // We only peek out WM_PAINT and WM_TIMER here for reasons mentioned above.
michael@0:     have_message = PeekMessage(&msg, NULL, WM_PAINT, WM_PAINT, PM_REMOVE) ||
michael@0:                    PeekMessage(&msg, NULL, WM_TIMER, WM_TIMER, PM_REMOVE);
michael@0:   } else {
michael@0:     have_message = (0 != PeekMessage(&msg, NULL, 0, 0, PM_REMOVE));
michael@0: 
michael@0:     if (have_message && msg.message == WM_NULL)
michael@0:       have_message = (0 != PeekMessage(&msg, NULL, 0, 0, PM_REMOVE));
michael@0:   }
michael@0: 
michael@0:   DCHECK(!have_message || kMsgHaveWork != msg.message ||
michael@0:          msg.hwnd != message_hwnd_);
michael@0: 
michael@0:   // Since we discarded a kMsgHaveWork message, we must update the flag.
michael@0:   int old_have_work = InterlockedExchange(&have_work_, 0);
michael@0:   DCHECK(old_have_work);
michael@0: 
michael@0:   // We don't need a special time slice if we didn't have_message to process.
michael@0:   if (!have_message)
michael@0:     return false;
michael@0: 
michael@0:   // Guarantee we'll get another time slice in the case where we go into native
michael@0:   // windows code.   This ScheduleWork() may hurt performance a tiny bit when
michael@0:   // tasks appear very infrequently, but when the event queue is busy, the
michael@0:   // kMsgHaveWork events get (percentage wise) rarer and rarer.
michael@0:   ScheduleWork();
michael@0:   return ProcessMessageHelper(msg);
michael@0: }
michael@0: 
michael@0: //-----------------------------------------------------------------------------
michael@0: // MessagePumpForIO public:
michael@0: 
michael@0: MessagePumpForIO::MessagePumpForIO() {
michael@0:   port_.Set(CreateIoCompletionPort(INVALID_HANDLE_VALUE, NULL, 0, 1));
michael@0:   DCHECK(port_.IsValid());
michael@0: }
michael@0: 
michael@0: void MessagePumpForIO::ScheduleWork() {
michael@0:   if (InterlockedExchange(&have_work_, 1))
michael@0:     return;  // Someone else continued the pumping.
michael@0: 
michael@0:   // Make sure the MessagePump does some work for us.
michael@0:   BOOL ret = PostQueuedCompletionStatus(port_, 0,
michael@0:                                         reinterpret_cast<ULONG_PTR>(this),
michael@0:                                         reinterpret_cast<OVERLAPPED*>(this));
michael@0:   DCHECK(ret);
michael@0: }
michael@0: 
michael@0: void MessagePumpForIO::ScheduleDelayedWork(const TimeTicks& delayed_work_time) {
michael@0:   // We know that we can't be blocked right now since this method can only be
michael@0:   // called on the same thread as Run, so we only need to update our record of
michael@0:   // how long to sleep when we do sleep.
michael@0:   delayed_work_time_ = delayed_work_time;
michael@0: }
michael@0: 
michael@0: void MessagePumpForIO::RegisterIOHandler(HANDLE file_handle,
michael@0:                                          IOHandler* handler) {
michael@0:   ULONG_PTR key = reinterpret_cast<ULONG_PTR>(handler);
michael@0:   HANDLE port = CreateIoCompletionPort(file_handle, port_, key, 1);
michael@0:   DCHECK(port == port_.Get());
michael@0: }
michael@0: 
michael@0: //-----------------------------------------------------------------------------
michael@0: // MessagePumpForIO private:
michael@0: 
michael@0: void MessagePumpForIO::DoRunLoop() {
michael@0:   for (;;) {
michael@0:     // If we do any work, we may create more messages etc., and more work may
michael@0:     // possibly be waiting in another task group.  When we (for example)
michael@0:     // WaitForIOCompletion(), there is a good chance there are still more
michael@0:     // messages waiting.  On the other hand, when any of these methods return
michael@0:     // having done no work, then it is pretty unlikely that calling them
michael@0:     // again quickly will find any work to do.  Finally, if they all say they
michael@0:     // had no work, then it is a good time to consider sleeping (waiting) for
michael@0:     // more work.
michael@0: 
michael@0:     bool more_work_is_plausible = state_->delegate->DoWork();
michael@0:     if (state_->should_quit)
michael@0:       break;
michael@0: 
michael@0:     more_work_is_plausible |= WaitForIOCompletion(0, NULL);
michael@0:     if (state_->should_quit)
michael@0:       break;
michael@0: 
michael@0:     more_work_is_plausible |=
michael@0:         state_->delegate->DoDelayedWork(&delayed_work_time_);
michael@0:     if (state_->should_quit)
michael@0:       break;
michael@0: 
michael@0:     if (more_work_is_plausible)
michael@0:       continue;
michael@0: 
michael@0:     more_work_is_plausible = state_->delegate->DoIdleWork();
michael@0:     if (state_->should_quit)
michael@0:       break;
michael@0: 
michael@0:     if (more_work_is_plausible)
michael@0:       continue;
michael@0: 
michael@0:     WaitForWork();  // Wait (sleep) until we have work to do again.
michael@0:   }
michael@0: }
michael@0: 
michael@0: // Wait until IO completes, up to the time needed by the timer manager to fire
michael@0: // the next set of timers.
michael@0: void MessagePumpForIO::WaitForWork() {
michael@0:   // We do not support nested IO message loops. This is to avoid messy
michael@0:   // recursion problems.
michael@0:   DCHECK(state_->run_depth == 1) << "Cannot nest an IO message loop!";
michael@0: 
michael@0:   int timeout = GetCurrentDelay();
michael@0:   if (timeout < 0)  // Negative value means no timers waiting.
michael@0:     timeout = INFINITE;
michael@0: 
michael@0:   WaitForIOCompletion(timeout, NULL);
michael@0: }
michael@0: 
michael@0: bool MessagePumpForIO::WaitForIOCompletion(DWORD timeout, IOHandler* filter) {
michael@0:   IOItem item;
michael@0:   if (completed_io_.empty() || !MatchCompletedIOItem(filter, &item)) {
michael@0:     // We have to ask the system for another IO completion.
michael@0:     if (!GetIOItem(timeout, &item))
michael@0:       return false;
michael@0: 
michael@0:     if (ProcessInternalIOItem(item))
michael@0:       return true;
michael@0:   }
michael@0: 
michael@0:   if (item.context->handler) {
michael@0:     if (filter && item.handler != filter) {
michael@0:       // Save this item for later
michael@0:       completed_io_.push_back(item);
michael@0:     } else {
michael@0:       DCHECK(item.context->handler == item.handler);
michael@0:       item.handler->OnIOCompleted(item.context, item.bytes_transfered,
michael@0:                                   item.error);
michael@0:     }
michael@0:   } else {
michael@0:     // The handler must be gone by now, just cleanup the mess.
michael@0:     delete item.context;
michael@0:   }
michael@0:   return true;
michael@0: }
michael@0: 
michael@0: // Asks the OS for another IO completion result.
michael@0: bool MessagePumpForIO::GetIOItem(DWORD timeout, IOItem* item) {
michael@0:   memset(item, 0, sizeof(*item));
michael@0:   ULONG_PTR key = 0;
michael@0:   OVERLAPPED* overlapped = NULL;
michael@0:   if (!GetQueuedCompletionStatus(port_.Get(), &item->bytes_transfered, &key,
michael@0:                                  &overlapped, timeout)) {
michael@0:     if (!overlapped)
michael@0:       return false;  // Nothing in the queue.
michael@0:     item->error = GetLastError();
michael@0:     item->bytes_transfered = 0;
michael@0:   }
michael@0: 
michael@0:   item->handler = reinterpret_cast<IOHandler*>(key);
michael@0:   item->context = reinterpret_cast<IOContext*>(overlapped);
michael@0:   return true;
michael@0: }
michael@0: 
michael@0: bool MessagePumpForIO::ProcessInternalIOItem(const IOItem& item) {
michael@0:   if (this == reinterpret_cast<MessagePumpForIO*>(item.context) &&
michael@0:       this == reinterpret_cast<MessagePumpForIO*>(item.handler)) {
michael@0:     // This is our internal completion.
michael@0:     DCHECK(!item.bytes_transfered);
michael@0:     InterlockedExchange(&have_work_, 0);
michael@0:     return true;
michael@0:   }
michael@0:   return false;
michael@0: }
michael@0: 
michael@0: // Returns a completion item that was previously received.
michael@0: bool MessagePumpForIO::MatchCompletedIOItem(IOHandler* filter, IOItem* item) {
michael@0:   DCHECK(!completed_io_.empty());
michael@0:   for (std::list<IOItem>::iterator it = completed_io_.begin();
michael@0:        it != completed_io_.end(); ++it) {
michael@0:     if (!filter || it->handler == filter) {
michael@0:       *item = *it;
michael@0:       completed_io_.erase(it);
michael@0:       return true;
michael@0:     }
michael@0:   }
michael@0:   return false;
michael@0: }
michael@0: 
michael@0: }  // namespace base