blob: ae022bf0957f48be47ad16c77b0f0d99693add21 [file] [log] [blame]
// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "base/message_loop/message_pump_win.h"
#include <math.h>
#include "base/debug/trace_event.h"
#include "base/message_loop/message_loop.h"
#include "base/metrics/histogram.h"
#include "base/process/memory.h"
#include "base/strings/stringprintf.h"
#include "base/win/wrapped_window_proc.h"
namespace base {
namespace {
enum MessageLoopProblems {
} // namespace
static const wchar_t kWndClassFormat[] = L"Chrome_MessagePumpWindow_%p";
// Message sent to get an additional time slice for pumping (processing) another
// task (a series of such messages creates a continuous task pump).
static const int kMsgHaveWork = WM_USER + 1;
// MessagePumpWin public:
void MessagePumpWin::AddObserver(MessagePumpObserver* observer) {
void MessagePumpWin::RemoveObserver(MessagePumpObserver* 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;
state_ = previous_state;
void MessagePumpWin::Quit() {
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:
: atom_(0) {
MessagePumpForUI::~MessagePumpForUI() {
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.
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)
// 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.
// MessagePumpForUI private:
// static
LRESULT CALLBACK MessagePumpForUI::WndProcThunk(
HWND hwnd, UINT message, WPARAM wparam, LPARAM lparam) {
switch (message) {
case kMsgHaveWork:
case WM_TIMER:
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)
more_work_is_plausible |= state_->delegate->DoWork();
if (state_->should_quit)
more_work_is_plausible |=
// 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)
if (more_work_is_plausible)
more_work_is_plausible = state_->delegate->DoIdleWork();
if (state_->should_quit)
if (more_work_is_plausible)
WaitForWork(); // Wait (sleep) until we have work to do again.
void MessagePumpForUI::InitMessageWnd() {
// Generate a unique window class name.
string16 class_name = StringPrintf(kWndClassFormat, this);
HINSTANCE instance = GetModuleFromAddress(&WndProcThunk);
WNDCLASSEX wc = {0};
wc.cbSize = sizeof(wc);
wc.lpfnWndProc = base::win::WrappedWindowProc<WndProcThunk>;
wc.hInstance = instance;
wc.lpszClassName = class_name.c_str();
atom_ = RegisterClassEx(&wc);
message_hwnd_ = CreateWindow(MAKEINTATOM(atom_), 0, 0, 0, 0, 0, 0,
HWND_MESSAGE, 0, instance, 0);
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,
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 &&
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);
// 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.
// 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())
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_)
if (!delayed_work_time_.is_null()) {
// A bit gratuitous to set delayed_work_time_ again, but oh well.
bool MessagePumpForUI::ProcessNextWindowsMessage() {
// If there are sent messages in the queue then PeekMessage internally
// dispatches the message and returns false. We return true in this
// case to ensure that the message loop peeks again instead of calling
// MsgWaitForMultipleObjectsEx again.
bool sent_messages_in_queue = false;
DWORD queue_status = GetQueueStatus(QS_SENDMESSAGE);
if (HIWORD(queue_status) & QS_SENDMESSAGE)
sent_messages_in_queue = true;
MSG msg;
if (PeekMessage(&msg, NULL, 0, 0, PM_REMOVE) != FALSE)
return ProcessMessageHelper(msg);
return sent_messages_in_queue;
bool MessagePumpForUI::ProcessMessageHelper(const MSG& msg) {
TRACE_EVENT1("base", "MessagePumpForUI::ProcessMessageHelper",
"message", msg.message);
if (WM_QUIT == msg.message) {
// Repost the QUIT message so that it will be retrieved by the primary
// GetMessage() loop.
state_->should_quit = true;
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;
uint32_t action = MessagePumpDispatcher::POST_DISPATCH_PERFORM_DEFAULT;
if (state_->dispatcher)
action = state_->dispatcher->Dispatch(msg);
if (action & MessagePumpDispatcher::POST_DISPATCH_QUIT_LOOP)
state_->should_quit = true;
if (action & MessagePumpDispatcher::POST_DISPATCH_PERFORM_DEFAULT) {
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) ||
} else {
have_message = PeekMessage(&msg, NULL, 0, 0, PM_REMOVE) != FALSE;
DCHECK(!have_message || kMsgHaveWork != msg.message ||
msg.hwnd != message_hwnd_);
// Since we discarded a kMsgHaveWork message, we must update the flag.
int old_have_work = InterlockedExchange(&have_work_, 0);
// 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.
return ProcessMessageHelper(msg);
// MessagePumpForIO public:
MessagePumpForIO::MessagePumpForIO() {
port_.Set(CreateIoCompletionPort(INVALID_HANDLE_VALUE, NULL, NULL, 1));
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,
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.
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);
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);
info.CompletionKey = reinterpret_cast<void*>(key);
info.CompletionPort = port_;
return SetInformationJobObject(job_handle,
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)
more_work_is_plausible |= WaitForIOCompletion(0, NULL);
if (state_->should_quit)
more_work_is_plausible |=
if (state_->should_quit)
if (more_work_is_plausible)
more_work_is_plausible = state_->delegate->DoIdleWork();
if (state_->should_quit)
if (more_work_is_plausible)
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
} else {
DCHECK(!item.has_valid_io_context ||
(item.context->handler == item.handler));
item.handler->OnIOCompleted(item.context, item.bytes_transfered,
} 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));
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.
InterlockedExchange(&have_work_, 0);
return true;
return false;
// Returns a completion item that was previously received.
bool MessagePumpForIO::MatchCompletedIOItem(IOHandler* filter, IOItem* item) {
for (std::list<IOItem>::iterator it = completed_io_.begin();
it != completed_io_.end(); ++it) {
if (!filter || it->handler == filter) {
*item = *it;
return true;
return false;
void MessagePumpForIO::AddIOObserver(IOObserver *obs) {
void MessagePumpForIO::RemoveIOObserver(IOObserver *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(
bool* has_valid_io_context) {
*has_valid_io_context = ((key & 1) == 0);
return reinterpret_cast<IOHandler*>(key & ~static_cast<ULONG_PTR>(1));
} // namespace base