Don't peek messages in the MessagePumpForUI class when we receive our kMsgHaveWork message.

base/message_loop/message_pump_win.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/message_loop/message_pump_win.h"
 
 #include <limits>
 #include <math.h>
 
 #include "base/message_loop/message_loop.h"
 #include "base/metrics/histogram.h"
 #include "base/process/memory.h"
 #include "base/profiler/scoped_tracker.h"
 #include "base/strings/stringprintf.h"
+#include "base/threading/thread.h"
 #include "base/trace_event/trace_event.h"
 #include "base/win/wrapped_window_proc.h"
 
 namespace base {
 
 namespace {
 
 enum MessageLoopProblems {
   MESSAGE_POST_ERROR,
   COMPLETION_POST_ERROR,
@@ skipping 58 matching lines @@
       (timeout > std::numeric_limits<int>::max() ?
        std::numeric_limits<int>::max() : static_cast<int>(timeout));
 }
 
 //-----------------------------------------------------------------------------
 // MessagePumpForUI public:
 
 MessagePumpForUI::MessagePumpForUI()
     : atom_(0) {
   InitMessageWnd();
+
+  ui_worker_thread_timer_.Set(::CreateWaitableTimer(NULL, FALSE, NULL));
+  ui_worker_thread_.reset(new base::Thread("UI Pump Worker thread"));
+  ui_worker_thread_->Start();
+  ui_worker_thread_->task_runner()->PostTask(
+      FROM_HERE,
+      base::Bind(&MessagePumpForUI::DoWorkerThreadRunLoop,
+                 base::Unretained(this)));
 }
 
 MessagePumpForUI::~MessagePumpForUI() {
   DestroyWindow(message_hwnd_);
   UnregisterClass(MAKEINTATOM(atom_),
                   GetModuleFromAddress(&WndProcThunk));
+
+  ::QueueUserAPC(
+        reinterpret_cast<PAPCFUNC>(&MessagePumpForUI::ShutdownWorkerThread),
+        ui_worker_thread_->thread_handle().platform_handle(), NULL);
+  ui_worker_thread_->Stop();
 }
 
 void MessagePumpForUI::ScheduleWork() {
-  if (InterlockedExchange(&have_work_, 1))
-    return;  // Someone else continued the pumping.
+  // If we have a regular posted task at the head of queue then we need to
+  // process it quickly.
+  if (state_ && state_->delegate->GetNewlyAddedTaskDelay().is_null()) {
+    // Make sure the MessagePump does some work for us.
+    PostWorkMessage();
+    return;
+  }
 
-  // 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);
+  LARGE_INTEGER due_time = {0};
+  // Set the timer to fire every 3 milliseconds. The actual resolution of the
+  // timer is dependent on timeBeginPeriod being called.
+  due_time.QuadPart = -30000;

[scottmg, 2015/06/08 21:43:31]

How did we pick 3?

[ananta, 2015/06/08 21:46:54]

That was a consensus number based on the fact that the fastest our timers run
are 3 milliseconds for AC and 4 for battery

+  BOOL ret = ::SetWaitableTimer(ui_worker_thread_timer_.Get(), &due_time, 3,
+      NULL, NULL, FALSE);
+  CHECK(ret);
 }
 
 void MessagePumpForUI::ScheduleDelayedWork(const TimeTicks& delayed_work_time) {
   delayed_work_time_ = delayed_work_time;
   RescheduleTimer();
 }
 
 //-----------------------------------------------------------------------------
 // MessagePumpForUI private:
 
@@ skipping 296 matching lines @@
         FROM_HERE_WITH_EXPLICIT_FUNCTION(
             "440919 MessagePumpForUI::ProcessMessageHelper6"));
 
     DispatchMessage(&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!!
+  // Since we discarded a kMsgHaveWork message, we must update the flag.
+  InterlockedExchange(&have_work_, 0);
+  return true;
+}
 
-  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 = PeekMessage(&msg, NULL, 0, 0, PM_REMOVE) != FALSE;
+void MessagePumpForUI::DoWorkerThreadRunLoop() {
+  DCHECK(ui_worker_thread_timer_.Get());
+  while (TRUE) {
+    DWORD ret = WaitForSingleObjectEx(
+        ui_worker_thread_timer_.Get(), INFINITE, TRUE);
+    // The only APC this thread could receive is the Shutdown APC.
+    if (ret == WAIT_IO_COMPLETION)
+      return;
+
+    // Make sure the MessagePump does some work for us.
+    PostWorkMessage();

[scottmg, 2015/06/08 21:43:31]

Is it possible for this only to runwhen SetNestableTasksAllowed or
set_os_modal_loop or whatever? Or does it already do that somehow?

[ananta, 2015/06/08 21:46:54]

It does not do that. Tricky to detect modal loops anyways. The only consumer of
set_os_modal loop is npapi plugins. We decided with the thread approach to avoid
our main pump peeking for other messages when we see our wake up message

   }
+}
 
-  DCHECK(!have_message || kMsgHaveWork != msg.message ||
-         msg.hwnd != message_hwnd_);
+// static
+void CALLBACK MessagePumpForUI::ShutdownWorkerThread(ULONG_PTR param) {
+  // This function is empty because we only use the fact that an APC was posted
+  // to the worker thread to shut it down.
+  return;
+}
 
-  // 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::PostWorkMessage() {
+  BOOL posted = PostMessage(message_hwnd_, kMsgHaveWork,
+                            reinterpret_cast<WPARAM>(this),
+                            0);
+  if (!posted) {
+    // 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.
+    UMA_HISTOGRAM_ENUMERATION("Chrome.MessageLoopProblem",
+                              MESSAGE_POST_ERROR,
+                              MESSAGE_LOOP_PROBLEM_MAX);
+  }
 }
 
 //-----------------------------------------------------------------------------
 // MessagePumpForIO public:
 
 MessagePumpForIO::MessagePumpForIO() {
   port_.Set(CreateIoCompletionPort(INVALID_HANDLE_VALUE, NULL, NULL, 1));
   DCHECK(port_.IsValid());
 }
 
@@ skipping 211 matching lines @@
 
 // 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