Improve the ui::MessageLoop waiting for events for a specific time

In this way we can remove the busy wait hack, and finally wait the
required time for an event or the next running ui::Timer that will
timeout.

laf

@@ -1 +1 @@
-Subproject commit b31ebd916c067af953d1d944f85ef5b5be520ebd
+Subproject commit f443e196b643d714986a42068393267493bbdc58

src/ui/manager.cpp

@@ -381,27 +381,29 @@ void Manager::generateMessagesFromOSEvents()
   // Events from laf-os
   os::Event osEvent;
   for (;;) {
-    // TODO Add timers to laf::os library so we can wait for then in
-    //      the OS message loop.
-    bool canWait = (msg_queue.empty() &&
-                    redrawState == RedrawState::Normal &&
-                    !Timer::haveRunningTimers());
+    // Calculate how much time we can wait for the next message in the
+    // event queue.
+    double timeout = 0.0;
+    if (msg_queue.empty() && redrawState == RedrawState::Normal) {
+      if (!Timer::getNextTimeout(timeout))
+        timeout = os::EventQueue::kWithoutTimeout;
+    }
 
-    if (canWait && used_msg_queue.empty())
+    if (timeout == os::EventQueue::kWithoutTimeout && used_msg_queue.empty())
       collectGarbage();
 #if _DEBUG
     else if (!m_garbage.empty()) {
       GARBAGE_TRACE("collectGarbage() wasn't called #objects=%d"
-                    " (msg_queue=%d used_msg_queue=%d redrawState=%d runningTimers=%d)\n",
+                    " (msg_queue=%d used_msg_queue=%d redrawState=%d timeout=%.16g)\n",
                     int(m_garbage.size()),
                     msg_queue.size(),
                     used_msg_queue.size(),
                     int(redrawState),
-                    Timer::haveRunningTimers());
+                    timeout);
     }
 #endif
 
-    m_eventQueue->getEvent(osEvent, canWait);
+    m_eventQueue->getEvent(osEvent, timeout);
     if (osEvent.type() == os::Event::None)
       break;
 

src/ui/message_loop.cpp

@@ -1,4 +1,5 @@
 // Aseprite UI Library
+// Copyright (C) 2021  Igara Studio S.A.
 // Copyright (C) 2001-2013  David Capello
 //
 // This file is released under the terms of the MIT license.
@@ -10,8 +11,6 @@
 
 #include "ui/message_loop.h"
 
-#include "base/chrono.h"
-#include "base/thread.h"
 #include "ui/manager.h"
 
 namespace ui {
@@ -23,22 +22,8 @@ MessageLoop::MessageLoop(Manager* manager)
 
 void MessageLoop::pumpMessages()
 {
-  base::Chrono chrono;
-
   if (m_manager->generateMessages())
     m_manager->dispatchMessages();
-
-  // If the dispatching of messages was faster than 10 milliseconds,
-  // it means that the process is not using a lot of CPU, so we can
-  // wait the difference to cover those 10 milliseconds
-  // sleeping. With this code we can avoid 100% CPU usage.
-  //
-  // TODO check if we require this code, after adding support of event
-  //      queues that wait for events.
-  //
-  double elapsedMSecs = chrono.elapsed() * 1000.0;
-  if (elapsedMSecs > 0.0 && elapsedMSecs < 10.0)
-    base::this_thread::sleep_for((10.0 - elapsedMSecs) / 1000.0);
 }
 
 } // namespace ui

src/ui/timer.cpp

@@ -1,5 +1,5 @@
 // Aseprite UI Library
-// Copyright (C) 2018  Igara Studio S.A.
+// Copyright (C) 2018-2021  Igara Studio S.A.
 // Copyright (C) 2001-2017  David Capello
 //
 // This file is released under the terms of the MIT license.
@@ -18,6 +18,7 @@
 #include "ui/widget.h"
 
 #include <algorithm>
+#include <limits>
 #include <vector>
 
 namespace ui {
@@ -128,9 +129,28 @@ bool Timer::haveTimers()
   return !timers.empty();
 }
 
-bool Timer::haveRunningTimers()
+bool Timer::getNextTimeout(double& timeout)
 {
-  return (running_timers != 0);
+  if (running_timers == 0)
+    return false;
+
+  base::tick_t t = base::current_tick();
+  bool result = false;
+  timeout = std::numeric_limits<double>::max();
+  for (auto timer : timers) {
+    if (timer && timer->isRunning()) {
+      int64_t diff = (timer->m_lastTick + timer->m_interval) - t;
+      if (diff < 0) {
+        timeout = 0.0;         // Right-now
+        return true;
+      }
+      else {
+        timeout = std::min<double>(timeout, diff / 1000.0);
+        result = true;
+      }
+    }
+  }
+  return result;
 }
 
 } // namespace ui

src/ui/timer.h

@@ -1,5 +1,5 @@
 // Aseprite UI Library
-// Copyright (C) 2020  Igara Studio S.A.
+// Copyright (C) 2020-2021  Igara Studio S.A.
 // Copyright (C) 2001-2016  David Capello
 //
 // This file is released under the terms of the MIT license.
@@ -38,7 +38,7 @@ namespace ui {
 
     static void pollTimers();
     static bool haveTimers();
-    static bool haveRunningTimers();
+    static bool getNextTimeout(double& timeout);
 
   protected:
     virtual void onTick();