// Copyright 2012 The Chromium Authors
// 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 <winbase.h>
#include <algorithm>
#include <atomic>
#include <cstdint>
#include <type_traits>
#include "base/auto_reset.h"
#include "base/check.h"
#include "base/debug/alias.h"
#include "base/debug/dump_without_crashing.h"
#include "base/debug/stack_trace.h"
#include "base/feature_list.h"
#include "base/functional/bind.h"
#include "base/memory/raw_ptr.h"
#include "base/metrics/histogram_macros.h"
#include "base/numerics/safe_conversions.h"
#include "base/strings/stringprintf.h"
#include "base/task/task_features.h"
#include "base/trace_event/base_tracing.h"
#include "base/tracing_buildflags.h"
#if BUILDFLAG(ENABLE_BASE_TRACING)
#include "third_party/perfetto/protos/perfetto/trace/track_event/chrome_message_pump.pbzero.h" // nogncheck
#endif // BUILDFLAG(ENABLE_BASE_TRACING)
namespace base {
namespace {
// Returns the number of milliseconds before |next_task_time|, clamped between
// zero and the biggest DWORD value (or INFINITE if |next_task_time.is_max()|).
// Optionally, a recent value of Now() may be passed in to avoid resampling it.
DWORD GetSleepTimeoutMs(TimeTicks next_task_time,
TimeTicks recent_now = TimeTicks()) {
// Shouldn't need to sleep or install a timer when there's pending immediate
// work.
DCHECK(!next_task_time.is_null());
if (next_task_time.is_max())
return INFINITE;
auto now = recent_now.is_null() ? TimeTicks::Now() : recent_now;
auto timeout_ms = (next_task_time - now).InMillisecondsRoundedUp();
// A saturated_cast with an unsigned destination automatically clamps negative
// values at zero.
static_assert(!std::is_signed_v<DWORD>, "DWORD is unexpectedly signed");
return saturated_cast<DWORD>(timeout_ms);
}
bool g_ui_pump_improvements_win = false;
} // 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;
MessagePumpWin::~MessagePumpWin() = default;
// static
void MessagePumpWin::InitializeFeatures() {
g_ui_pump_improvements_win = FeatureList::IsEnabled(kUIPumpImprovementsWin);
}
void MessagePumpWin::Run(Delegate* delegate) {
DCHECK_CALLED_ON_VALID_THREAD(bound_thread_);
RunState run_state(delegate);
if (run_state_)
run_state.is_nested = true;
AutoReset<raw_ptr<RunState>> auto_reset_run_state(&run_state_, &run_state);
DoRunLoop();
}
void MessagePumpWin::Quit() {
DCHECK_CALLED_ON_VALID_THREAD(bound_thread_);
DCHECK(run_state_);
run_state_->should_quit = true;
}
//-----------------------------------------------------------------------------
// MessagePumpForUI public:
MessagePumpForUI::MessagePumpForUI() {
bool succeeded = message_window_.Create(
BindRepeating(&MessagePumpForUI::MessageCallback, Unretained(this)));
CHECK(succeeded) << "Failed to create message-only Window with error"
<< StringPrintf("0x%08x",
static_cast<unsigned int>(::GetLastError()));
}
MessagePumpForUI::~MessagePumpForUI() = default;
void MessagePumpForUI::ScheduleWork() {
// This is the only MessagePumpForUI method which can be called outside of
// |bound_thread_|.
if (g_ui_pump_improvements_win &&
!in_nested_native_loop_with_application_tasks_) {
// The pump is running using `event_` as its chrome-side synchronization
// variable. In this case, no deduplication is done, since the event has its
// own state.
event_.Signal();
return;
}
bool not_scheduled = false;
if (!native_msg_scheduled_.compare_exchange_strong(
not_scheduled, true, std::memory_order_relaxed)) {
return; // Someone else continued the pumping.
}
const 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.
native_msg_scheduled_.store(false, std::memory_order_relaxed);
TRACE_EVENT_INSTANT0("base", "Chrome.MessageLoopProblem.MESSAGE_POST_ERROR",
TRACE_EVENT_SCOPE_THREAD);
}
void MessagePumpForUI::ScheduleDelayedWork(
const Delegate::NextWorkInfo& next_work_info) {
DCHECK_CALLED_ON_VALID_THREAD(bound_thread_);
// Since this is always called from |bound_thread_|, there is almost always
// nothing to do as the loop is already running. When the loop becomes idle,
// it will typically WaitForWork() in DoRunLoop() with the timeout provided by
// DoWork(). The only alternative to this is entering a native nested loop
// (e.g. modal dialog) under a
// `ScopedAllowApplicationTasksInNativeNestedLoop`, in which case
// HandleWorkMessage() will be invoked when the system picks up kMsgHaveWork
// and it will ScheduleNativeTimer() if it's out of immediate work. However,
// in that alternate scenario : it's possible for a Windows native work item
// (e.g. https://docs.microsoft.com/en-us/windows/desktop/winmsg/using-hooks)
// to wake the native nested loop and PostDelayedTask() to the current thread
// from it. This is the only case where we must install/adjust the native
// timer from ScheduleDelayedWork() because if we don't, the native loop will
// go back to sleep, unaware of the new |delayed_work_time|.
// See MessageLoopTest.PostDelayedTaskFromSystemPump for an example.
// TODO(gab): This could potentially be replaced by a ForegroundIdleProc hook
// if Windows ends up being the only platform requiring ScheduleDelayedWork().
if (in_nested_native_loop_with_application_tasks_ &&
!native_msg_scheduled_.load(std::memory_order_relaxed)) {
ScheduleNativeTimer(next_work_info);
}
}
bool MessagePumpForUI::HandleNestedNativeLoopWithApplicationTasks(
bool application_tasks_desired) {
// It is here assumed that we will be in a native loop until either
// DoRunLoop() gets control back, or this is called with `false`, and thus the
// Windows event queue is to be used for synchronization. This is to prevent
// being unable to wake up for application tasks in the case of a nested loop.
in_nested_native_loop_with_application_tasks_ = application_tasks_desired;
if (application_tasks_desired) {
ScheduleWork();
}
return true;
}
void MessagePumpForUI::AddObserver(Observer* observer) {
DCHECK_CALLED_ON_VALID_THREAD(bound_thread_);
observers_.AddObserver(observer);
}
void MessagePumpForUI::RemoveObserver(Observer* observer) {
DCHECK_CALLED_ON_VALID_THREAD(bound_thread_);
observers_.RemoveObserver(observer);
}
//-----------------------------------------------------------------------------
// MessagePumpForUI private:
bool MessagePumpForUI::MessageCallback(
UINT message, WPARAM wparam, LPARAM lparam, LRESULT* result) {
DCHECK_CALLED_ON_VALID_THREAD(bound_thread_);
switch (message) {
case kMsgHaveWork:
HandleWorkMessage();
break;
case WM_TIMER:
if (wparam == reinterpret_cast<UINT_PTR>(this))
HandleTimerMessage();
break;
}
return false;
}
void MessagePumpForUI::DoRunLoop() {
DCHECK_CALLED_ON_VALID_THREAD(bound_thread_);
// 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).
wakeup_state_ = WakeupState::kRunning;
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.
in_nested_native_loop_with_application_tasks_ = false;
bool more_work_is_plausible = false;
if (!g_ui_pump_improvements_win ||
wakeup_state_ != WakeupState::kApplicationTask) {
more_work_is_plausible |= ProcessNextWindowsMessage();
// We can end up in native loops which allow application tasks outside of
// DoWork() when Windows calls back a Win32 message window owned by some
// Chromium code.
in_nested_native_loop_with_application_tasks_ = false;
if (run_state_->should_quit) {
break;
}
}
Delegate::NextWorkInfo next_work_info = run_state_->delegate->DoWork();
// Since nested native loops with application tasks are initiated by a
// scoper, they should always be cleared before exiting DoWork().
DCHECK(!in_nested_native_loop_with_application_tasks_);
wakeup_state_ = WakeupState::kRunning;
more_work_is_plausible |= next_work_info.is_immediate();
if (run_state_->should_quit) {
break;
}
if (installed_native_timer_) {
// As described in ScheduleNativeTimer(), the native timer is only
// installed and needed while in a nested native loop. If it is installed,
// it means the above work entered such a loop. Having now resumed, the
// native timer is no longer needed.
KillNativeTimer();
}
if (more_work_is_plausible)
continue;
run_state_->delegate->DoIdleWork();
// DoIdleWork() shouldn't end up in native nested loops, nor should it
// permit native nested loops, and thus shouldn't have any chance of
// reinstalling a native timer.
DCHECK(!in_nested_native_loop_with_application_tasks_);
DCHECK(!installed_native_timer_);
if (run_state_->should_quit) {
break;
}
WaitForWork(next_work_info);
}
}
void MessagePumpForUI::WaitForWork(Delegate::NextWorkInfo next_work_info) {
DCHECK_CALLED_ON_VALID_THREAD(bound_thread_);
// Wait until a message is available, up to the time needed by the timer
// manager to fire the next set of timers.
DWORD wait_flags = MWMO_INPUTAVAILABLE;
bool last_wakeup_was_spurious = false;
for (DWORD delay = GetSleepTimeoutMs(next_work_info.delayed_run_time,
next_work_info.recent_now);
delay != 0; delay = GetSleepTimeoutMs(next_work_info.delayed_run_time)) {
if (!last_wakeup_was_spurious) {
run_state_->delegate->BeforeWait();
}
last_wakeup_was_spurious = false;
// Tell the optimizer to retain these values to simplify analyzing hangs.
base::debug::Alias(&delay);
base::debug::Alias(&wait_flags);
DWORD result;
if (g_ui_pump_improvements_win) {
HANDLE event_handle = event_.handle();
result = MsgWaitForMultipleObjectsEx(1, &event_handle, delay, QS_ALLINPUT,
wait_flags);
DPCHECK(WAIT_FAILED != result);
if (result == WAIT_OBJECT_0) {
wakeup_state_ = WakeupState::kApplicationTask;
} else if (result == WAIT_OBJECT_0 + 1) {
wakeup_state_ = WakeupState::kNative;
} else {
wakeup_state_ = WakeupState::kInactive;
}
} else {
result = MsgWaitForMultipleObjectsEx(0, nullptr, delay, QS_ALLINPUT,
wait_flags);
DPCHECK(WAIT_FAILED != result);
if (result == WAIT_OBJECT_0) {
wakeup_state_ = WakeupState::kNative;
} else {
wakeup_state_ = WakeupState::kInactive;
}
}
if (wakeup_state_ == WakeupState::kApplicationTask) {
// This can only be reached when the pump woke up via `event_`. In that
// case, tasks are prioritized over native.
return;
} else if (wakeup_state_ == WakeupState::kNative) {
// 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.
// As in ProcessNextWindowsMessage().
auto scoped_do_work_item = run_state_->delegate->BeginWorkItem();
{
TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("base"),
"MessagePumpForUI::WaitForWork GetQueueStatus");
if (HIWORD(::GetQueueStatus(QS_SENDMESSAGE)) & QS_SENDMESSAGE)
return;
}
{
MSG msg;
TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("base"),
"MessagePumpForUI::WaitForWork PeekMessage");
if (::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;
} else {
DCHECK_EQ(wakeup_state_, WakeupState::kInactive);
last_wakeup_was_spurious = true;
TRACE_EVENT_INSTANT(
"base", "MessagePumpForUI::WaitForWork Spurious Wakeup",
[&](perfetto::EventContext ctx) {
ctx.event<perfetto::protos::pbzero::ChromeTrackEvent>()
->set_chrome_message_pump_for_ui()
->set_wait_for_object_result(result);
});
}
}
}
void MessagePumpForUI::HandleWorkMessage() {
DCHECK_CALLED_ON_VALID_THREAD(bound_thread_);
if (!g_ui_pump_improvements_win && in_dispatch_message_ &&
!in_nested_native_loop_with_application_tasks_) {
// An undeclared nested native loop is spinning in DispatchMessage(), which
// will pump application tasks (task execution is not disabled since
// DoWork() is not on the stack). Since UIPumpImprovementsWin will break
// this use case (application tasks will no longer run because kMsgHaveWork
// is not pumped), investigation is being done into stacks where this occurs
// and whether they need to be remediated.
//
// A `StackTrace` is used to deduplicate stacks to ensure that all instances
// of undeclared nested runloops are detected during a session.
//
// TODO(crbug.com/335672561): Remove this once data has been analyzed.
uintptr_t id = 0;
for (const void* address : debug::StackTrace().addresses()) {
id ^= reinterpret_cast<uintptr_t>(address);
}
debug::DumpWithoutCrashingWithUniqueId(id);
}
// 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 (!run_state_) {
// Since we handled a kMsgHaveWork message, we must still update this flag.
native_msg_scheduled_.store(false, std::memory_order_relaxed);
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();
Delegate::NextWorkInfo next_work_info = run_state_->delegate->DoWork();
if (next_work_info.is_immediate()) {
ScheduleWork();
} else {
run_state_->delegate->BeforeWait();
ScheduleNativeTimer(next_work_info);
}
}
void MessagePumpForUI::HandleTimerMessage() {
DCHECK_CALLED_ON_VALID_THREAD(bound_thread_);
// ::KillTimer doesn't remove pending WM_TIMER messages from the queue,
// explicitly ignore the last WM_TIMER message in that case to avoid handling
// work from here when DoRunLoop() is active (which could result in scheduling
// work from two places at once). Note: we're still fine in the event that a
// second native nested loop is entered before such a dead WM_TIMER message is
// discarded because ::SetTimer merely resets the timer if invoked twice with
// the same id.
if (!installed_native_timer_)
return;
// We only need to fire once per specific delay, another timer may be
// scheduled below but we're done with this one.
KillNativeTimer();
// 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 (!run_state_)
return;
Delegate::NextWorkInfo next_work_info = run_state_->delegate->DoWork();
if (next_work_info.is_immediate()) {
ScheduleWork();
} else {
run_state_->delegate->BeforeWait();
ScheduleNativeTimer(next_work_info);
}
}
void MessagePumpForUI::ScheduleNativeTimer(
Delegate::NextWorkInfo next_work_info) {
DCHECK(!next_work_info.is_immediate());
// We should only ScheduleNativeTimer() under the new pump implementation
// while nested with application tasks.
DCHECK(!g_ui_pump_improvements_win ||
in_nested_native_loop_with_application_tasks_);
// Do not redundantly set the same native timer again if it was already set.
// This can happen when a nested native loop goes idle with pending delayed
// tasks, then gets woken up by an immediate task, and goes back to idle with
// the same pending delay. No need to kill the native timer if there is
// already one but the |delayed_run_time| has changed as ::SetTimer reuses the
// same id and will replace and reset the existing timer.
if (installed_native_timer_ &&
*installed_native_timer_ == next_work_info.delayed_run_time) {
return;
}
if (next_work_info.delayed_run_time.is_max())
return;
// We do not use native Windows timers in general as they have a poor, 10ms,
// granularity. Instead we rely on MsgWaitForMultipleObjectsEx's
// high-resolution timeout to sleep without timers in WaitForWork(). However,
// when entering a nested native ::GetMessage() loop (e.g. native modal
// windows) under a `ScopedAllowApplicationTasksInNativeNestedLoop`, we have
// to rely on a native timer when HandleWorkMessage() runs out of immediate
// work. Since `ScopedAllowApplicationTasksInNativeNestedLoop` invokes
// ScheduleWork() : we are guaranteed that HandleWorkMessage() will be called
// after entering a nested native loop that should process application
// tasks. But once HandleWorkMessage() is out of immediate work, ::SetTimer()
// is used to guarantee we are invoked again should the next delayed task
// expire before the nested native loop ends. The native timer being
// unnecessary once we return to our DoRunLoop(), we ::KillTimer when it
// resumes (nested native loops should be rare so we're not worried about
// ::SetTimer<=>::KillTimer churn). TODO(gab): The long-standing legacy
// dependency on the behavior of
// `ScopedAllowApplicationTasksInNativeNestedLoop` is unfortunate, would be
// nice to make this a MessagePump concept (instead of requiring impls to
// invoke ScheduleWork() one-way and no-op DoWork() the other way).
UINT delay_msec = strict_cast<UINT>(GetSleepTimeoutMs(
next_work_info.delayed_run_time, next_work_info.recent_now));
if (delay_msec == 0) {
ScheduleWork();
} else {
// TODO(gab): ::SetTimer()'s documentation claims it does this for us.
// Consider removing this safety net.
delay_msec = std::clamp(delay_msec, static_cast<UINT>(USER_TIMER_MINIMUM),
static_cast<UINT>(USER_TIMER_MAXIMUM));
// Tell the optimizer to retain the delay to simplify analyzing hangs.
base::debug::Alias(&delay_msec);
const UINT_PTR ret =
::SetTimer(message_window_.hwnd(), reinterpret_cast<UINT_PTR>(this),
delay_msec, nullptr);
if (ret) {
installed_native_timer_ = next_work_info.delayed_run_time;
return;
}
// This error is likely similar to MESSAGE_POST_ERROR (i.e. native queue is
// full). Since we only use ScheduleNativeTimer() in native nested loops
// this likely means this pump will not be given a chance to run application
// tasks until the nested loop completes.
TRACE_EVENT_INSTANT0("base", "Chrome.MessageLoopProblem.SET_TIMER_ERROR",
TRACE_EVENT_SCOPE_THREAD);
}
}
void MessagePumpForUI::KillNativeTimer() {
DCHECK(installed_native_timer_);
const bool success =
::KillTimer(message_window_.hwnd(), reinterpret_cast<UINT_PTR>(this));
DPCHECK(success);
installed_native_timer_.reset();
}
bool MessagePumpForUI::ProcessNextWindowsMessage() {
DCHECK_CALLED_ON_VALID_THREAD(bound_thread_);
MSG msg;
bool has_msg = false;
bool more_work_is_plausible = false;
{
// ::PeekMessage() may process sent and/or internal messages (regardless of
// |had_messages| as ::GetQueueStatus() is an optimistic check that may
// racily have missed an incoming event -- it doesn't hurt to have empty
// internal units of work when ::PeekMessage turns out to be a no-op).
// Instantiate |scoped_do_work| ahead of GetQueueStatus() so that
// trace events it emits fully outscope GetQueueStatus' events
// (GetQueueStatus() itself not being expected to do work; it's fine to use
// only one ScopedDoWorkItem for both calls -- we trace them independently
// just in case internal work stalls).
auto scoped_do_work_item = run_state_->delegate->BeginWorkItem();
{
// Individually trace ::GetQueueStatus and ::PeekMessage because sampling
// profiler is hinting that we're spending a surprising amount of time
// with these on top of the stack. Tracing will be able to tell us whether
// this is a bias of sampling profiler (e.g. kernel takes ::GetQueueStatus
// as an opportunity to swap threads and is more likely to schedule the
// sampling profiler's thread while the sampled thread is swapped out on
// this frame).
TRACE_EVENT0(
TRACE_DISABLED_BY_DEFAULT("base"),
"MessagePumpForUI::ProcessNextWindowsMessage GetQueueStatus");
DWORD queue_status = ::GetQueueStatus(QS_SENDMESSAGE);
// 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.
if (HIWORD(queue_status) & QS_SENDMESSAGE)
more_work_is_plausible = true;
}
{
// PeekMessage can run a message if there are sent messages, trace that
// and emit the boolean param to see if it ever janks independently (ref.
// comment on GetQueueStatus).
TRACE_EVENT(
TRACE_DISABLED_BY_DEFAULT("base"),
"MessagePumpForUI::ProcessNextWindowsMessage PeekMessage",
[&](perfetto::EventContext ctx) {
perfetto::protos::pbzero::ChromeMessagePump* msg_pump_data =
ctx.event()->set_chrome_message_pump();
msg_pump_data->set_sent_messages_in_queue(more_work_is_plausible);
});
has_msg = ::PeekMessage(&msg, nullptr, 0, 0, PM_REMOVE) != FALSE;
}
}
if (has_msg)
more_work_is_plausible |= ProcessMessageHelper(msg);
return more_work_is_plausible;
}
bool MessagePumpForUI::ProcessMessageHelper(const MSG& msg) {
DCHECK_CALLED_ON_VALID_THREAD(bound_thread_);
if (msg.message == WM_QUIT) {
// WM_QUIT is the standard way to exit a ::GetMessage() loop. Our
// MessageLoop has its own quit mechanism, so WM_QUIT is generally
// unexpected.
TRACE_EVENT_INSTANT0("base",
"Chrome.MessageLoopProblem.RECEIVED_WM_QUIT_ERROR",
TRACE_EVENT_SCOPE_THREAD);
return true;
}
// While running our main message pump, we discard kMsgHaveWork messages.
if (msg.message == kMsgHaveWork && msg.hwnd == message_window_.hwnd())
return ProcessPumpReplacementMessage();
run_state_->delegate->BeginNativeWorkBeforeDoWork();
auto scoped_do_work_item = run_state_->delegate->BeginWorkItem();
TRACE_EVENT("base,toplevel", "MessagePumpForUI DispatchMessage",
[&](perfetto::EventContext ctx) {
ctx.event<perfetto::protos::pbzero::ChromeTrackEvent>()
->set_chrome_message_pump_for_ui()
->set_message_id(msg.message);
});
for (Observer& observer : observers_)
observer.WillDispatchMSG(msg);
::TranslateMessage(&msg);
{
AutoReset<bool> reset(&in_dispatch_message_, true);
::DispatchMessage(&msg);
}
for (Observer& observer : observers_)
observer.DidDispatchMSG(msg);
return true;
}
bool MessagePumpForUI::ProcessPumpReplacementMessage() {
DCHECK_CALLED_ON_VALID_THREAD(bound_thread_);
// 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;
bool have_message = false;
{
// Note: Ideally this call wouldn't process sent-messages (as we already did
// that in the PeekMessage call that lead to receiving this kMsgHaveWork),
// but there's no way to specify this (omitting PM_QS_SENDMESSAGE as in
// crrev.com/791043 doesn't do anything). Hence this call must be considered
// as a potential work item.
auto scoped_do_work_item = run_state_->delegate->BeginWorkItem();
TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("base"),
"MessagePumpForUI::ProcessPumpReplacementMessage PeekMessage");
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.
DCHECK(native_msg_scheduled_.load(std::memory_order_relaxed));
native_msg_scheduled_.store(false, std::memory_order_relaxed);
// We don't need a special time slice if we didn't |have_message| to process.
if (!have_message)
return false;
if (msg.message == WM_QUIT) {
// 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(crbug.com/40595757) : Fix this.
// The return value is mostly irrelevant but return true like we would after
// processing a QuitClosure() task.
return true;
} else if (msg.message == WM_TIMER &&
msg.wParam == reinterpret_cast<UINT_PTR>(this)) {
// This happens when a native nested loop invokes HandleWorkMessage() =>
// ProcessPumpReplacementMessage() which finds the WM_TIMER message
// installed by ScheduleNativeTimer(). That message needs to be handled
// directly as handing it off to ProcessMessageHelper() below would cause an
// unnecessary ScopedDoWorkItem which may incorrectly lead the Delegate's
// heuristics to conclude that the DoWork() in HandleTimerMessage() is
// nested inside a native work item. It's also safe to skip the below
// ScheduleWork() as it is not mandatory before invoking DoWork() and
// HandleTimerMessage() handles re-installing the necessary followup
// messages.
HandleTimerMessage();
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::IOHandler::IOHandler(const Location& from_here)
: io_handler_location_(from_here) {}
MessagePumpForIO::IOHandler::~IOHandler() = default;
MessagePumpForIO::MessagePumpForIO() {
port_.Set(::CreateIoCompletionPort(INVALID_HANDLE_VALUE, nullptr,
reinterpret_cast<ULONG_PTR>(nullptr), 1));
DCHECK(port_.is_valid());
}
MessagePumpForIO::~MessagePumpForIO() = default;
void MessagePumpForIO::ScheduleWork() {
// This is the only MessagePumpForIO method which can be called outside of
// |bound_thread_|.
bool not_scheduled = false;
if (!native_msg_scheduled_.compare_exchange_strong(
not_scheduled, true, std::memory_order_relaxed)) {
return; // Work already scheduled.
}
// Make sure the MessagePump does some work for us.
const 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.
native_msg_scheduled_.store(
false, std::memory_order_relaxed); // Clarify that we didn't succeed.
TRACE_EVENT_INSTANT0("base",
"Chrome.MessageLoopProblem.COMPLETION_POST_ERROR",
TRACE_EVENT_SCOPE_THREAD);
}
void MessagePumpForIO::ScheduleDelayedWork(
const Delegate::NextWorkInfo& next_work_info) {
DCHECK_CALLED_ON_VALID_THREAD(bound_thread_);
// Since this is always called from |bound_thread_|, there is nothing to do as
// the loop is already running. It will WaitForWork() in
// DoRunLoop() with the correct timeout when it's out of immediate tasks.
}
HRESULT MessagePumpForIO::RegisterIOHandler(HANDLE file_handle,
IOHandler* handler) {
DCHECK_CALLED_ON_VALID_THREAD(bound_thread_);
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) {
DCHECK_CALLED_ON_VALID_THREAD(bound_thread_);
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() {
DCHECK_CALLED_ON_VALID_THREAD(bound_thread_);
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.
Delegate::NextWorkInfo next_work_info = run_state_->delegate->DoWork();
bool more_work_is_plausible = next_work_info.is_immediate();
if (run_state_->should_quit)
break;
more_work_is_plausible |= WaitForIOCompletion(0);
if (run_state_->should_quit)
break;
if (more_work_is_plausible)
continue;
run_state_->delegate->DoIdleWork();
if (run_state_->should_quit)
break;
run_state_->delegate->BeforeWait();
WaitForWork(next_work_info);
}
}
// Wait until IO completes, up to the time needed by the timer manager to fire
// the next set of timers.
void MessagePumpForIO::WaitForWork(Delegate::NextWorkInfo next_work_info) {
DCHECK_CALLED_ON_VALID_THREAD(bound_thread_);
// We do not support nested IO message loops. This is to avoid messy
// recursion problems.
DCHECK(!run_state_->is_nested) << "Cannot nest an IO message loop!";
DWORD timeout = GetSleepTimeoutMs(next_work_info.delayed_run_time,
next_work_info.recent_now);
// Tell the optimizer to retain these values to simplify analyzing hangs.
base::debug::Alias(&timeout);
WaitForIOCompletion(timeout);
}
bool MessagePumpForIO::WaitForIOCompletion(DWORD timeout) {
DCHECK_CALLED_ON_VALID_THREAD(bound_thread_);
IOItem item;
if (!GetIOItem(timeout, &item))
return false;
if (ProcessInternalIOItem(item))
return true;
run_state_->delegate->BeginNativeWorkBeforeDoWork();
auto scoped_do_work_item = run_state_->delegate->BeginWorkItem();
TRACE_EVENT(
"base,toplevel", "IOHandler::OnIOCompleted",
[&](perfetto::EventContext ctx) {
ctx.event()->set_chrome_message_pump()->set_io_handler_location_iid(
base::trace_event::InternedSourceLocation::Get(
&ctx, base::trace_event::TraceSourceLocation(
item.handler->io_handler_location())));
});
item.handler.ExtractAsDangling()->OnIOCompleted(
item.context.ExtractAsDangling(), item.bytes_transfered, item.error);
return true;
}
// Asks the OS for another IO completion result.
bool MessagePumpForIO::GetIOItem(DWORD timeout, IOItem* item) {
DCHECK_CALLED_ON_VALID_THREAD(bound_thread_);
ULONG_PTR key = reinterpret_cast<ULONG_PTR>(nullptr);
OVERLAPPED* overlapped = nullptr;
// Clear the value for the number of bytes transferred in case extracting the
// packet doesn't populate it.
item->bytes_transfered = 0;
if (!::GetQueuedCompletionStatus(port_.get(), &item->bytes_transfered, &key,
&overlapped, timeout)) {
if (!overlapped)
return false; // Nothing in the queue.
// A completion packet for a failed operation was processed. The Windows
// last error code pertains to the operation that failed.
item->error = ::GetLastError();
// The packet may have contained a value for the number of bytes
// transferred, so pass along whatever value was populated from it.
} else {
// The packet corresponded to an operation that succeeded, so clear out
// the error value so that the handler sees the operation as a success.
item->error = ERROR_SUCCESS;
}
item->handler = reinterpret_cast<IOHandler*>(key);
item->context = reinterpret_cast<IOContext*>(overlapped);
return true;
}
bool MessagePumpForIO::ProcessInternalIOItem(const IOItem& item) {
DCHECK_CALLED_ON_VALID_THREAD(bound_thread_);
if (reinterpret_cast<void*>(this) ==
reinterpret_cast<void*>(item.context.get()) &&
reinterpret_cast<void*>(this) ==
reinterpret_cast<void*>(item.handler.get())) {
// This is our internal completion.
DCHECK(!item.bytes_transfered);
native_msg_scheduled_.store(false, std::memory_order_relaxed);
return true;
}
return false;
}
} // namespace base
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