1 files changed, 686 insertions, 0 deletions
diff --git a/base/message_pump_win.cc b/base/message_pump_win.cc
new file mode 100644
index 0000000..dcbb320
--- /dev/null
+++ b/base/message_pump_win.cc
@@ -0,0 +1,686 @@
+// 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_pump_win.h"
+
+#include <math.h>
+
+#include "base/debug/trace_event.h"
+#include "base/message_loop.h"
+#include "base/metrics/histogram.h"
+#include "base/process_util.h"
+#include "base/stringprintf.h"
+#include "base/win/wrapped_window_proc.h"
+
+namespace {
+
+enum MessageLoopProblems {
+  MESSAGE_POST_ERROR,
+  COMPLETION_POST_ERROR,
+  SET_TIMER_ERROR,
+  MESSAGE_LOOP_PROBLEM_MAX,
+};
+
+}  // namespace
+
+namespace base {
+
+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),
+      message_filter_(new MessageFilter) {
+  InitMessageWnd();
+}
+
+MessagePumpForUI::~MessagePumpForUI() {
+  DestroyWindow(message_hwnd_);
+  UnregisterClass(MAKEINTATOM(atom_),
+                  base::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);
+}
+
+void MessagePumpForUI::PumpOutPendingPaintMessages() {
+  // If we are being called outside of the context of Run, then don't try to do
+  // any work.
+  if (!state_)
+    return;
+
+  // Create a mini-message-pump to force immediate processing of only Windows
+  // WM_PAINT messages.  Don't provide an infinite loop, but do enough peeking
+  // to get the job done.  Actual common max is 4 peeks, but we'll be a little
+  // safe here.
+  const int kMaxPeekCount = 20;
+  int peek_count;
+  for (peek_count = 0; peek_count < kMaxPeekCount; ++peek_count) {
+    MSG msg;
+    if (!PeekMessage(&msg, NULL, 0, 0, PM_REMOVE | PM_QS_PAINT))
+      break;
+    ProcessMessageHelper(msg);
+    if (state_->should_quit)  // Handle WM_QUIT.
+      break;
+  }
+  // Histogram what was really being used, to help to adjust kMaxPeekCount.
+  DHISTOGRAM_COUNTS("Loop.PumpOutPendingPaintMessages Peeks", peek_count);
+}
+
+//-----------------------------------------------------------------------------
+// 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 = base::StringPrintf(kWndClassFormat, this);
+
+  HINSTANCE instance = base::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 (message_filter_->DoPeekMessage(&msg, NULL, 0, 0, PM_REMOVE))
+    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);
+
+  if (!message_filter_->ProcessMessage(msg)) {
+    if (state_->dispatcher) {
+      if (!state_->dispatcher->Dispatch(msg))
+        state_->should_quit = true;
+    } else {
+      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 = !!message_filter_->DoPeekMessage(&msg, NULL, 0, 0,
+                                                    PM_REMOVE);
+  }
+
+  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);
+}
+
+void MessagePumpForUI::SetMessageFilter(
+    scoped_ptr<MessageFilter> message_filter) {
+  message_filter_ = message_filter.Pass();
+}
+
+//-----------------------------------------------------------------------------
+// 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