Piano: Use CEventLoop::wake() to trigger repaint from sound thread.

In order to repaint the GUI after the sound thread has produced some sweet
new waves, we post a CCustomEvent to the main thread's event loop and then
wake up that event loop via CEventLoop::wake().

Applications/Piano/PianoWidget.cpp

@@ -354,3 +354,11 @@ void PianoWidget::render_knobs(GPainter& painter)
     painter.draw_rect(wave_knob_rect, Color(r, g, b));
     painter.draw_text(wave_knob_rect, wave_name, TextAlignment::Center, Color(r, g, b));
 }
+
+void PianoWidget::event(CEvent& event)
+{
+    if (event.type() == CEvent::Custom) {
+        update();
+    }
+    GWidget::event(event);
+}

Applications/Piano/PianoWidget.h

@@ -16,6 +16,7 @@ private:
     virtual void paint_event(GPaintEvent&) override;
     virtual void keydown_event(GKeyEvent&) override;
     virtual void keyup_event(GKeyEvent&) override;
+    virtual void event(CEvent&) override;
 
     double w_sine(size_t);
     double w_saw(size_t);

Applications/Piano/main.cpp

@@ -1,40 +1,27 @@
 #include "Music.h"
 #include "PianoWidget.h"
-#include <LibCore/CFile.h>
-#include <LibCore/CNotifier.h>
 #include <LibAudio/AClientConnection.h>
+#include <LibCore/CFile.h>
+#include <LibCore/CThread.h>
 #include <LibGUI/GApplication.h>
 #include <LibGUI/GEventLoop.h>
 #include <LibGUI/GWindow.h>
 
-static int s_pipefds[2];
-
 int main(int argc, char** argv)
 {
     AClientConnection audio_connection;
     GApplication app(argc, argv);
 
-    pipe(s_pipefds);
-
     auto* window = new GWindow;
     window->set_title("Piano");
     window->set_rect(100, 100, 512, 512);
 
     auto* piano_widget = new PianoWidget;
     window->set_main_widget(piano_widget);
-
     window->show();
-
     window->set_icon_path("/res/icons/16x16/app-piano.png");
 
-    CNotifier notifier(s_pipefds[0], CNotifier::Read);
-    notifier.on_ready_to_read = [&] {
-        char buffer[32];
-        read(s_pipefds[1], buffer, sizeof(buffer));
-        piano_widget->update();
-    };
-
-    create_thread([](void* context) -> int {
+    CThread sound_thread([](void* context) -> int {
         auto* piano_widget = (PianoWidget*)context;
 
         CFile audio("/dev/audio");
@@ -47,10 +34,11 @@ int main(int argc, char** argv)
             u8 buffer[4096];
             piano_widget->fill_audio_buffer(buffer, sizeof(buffer));
             audio.write(buffer, sizeof(buffer));
-            char ch = '!';
-            write(s_pipefds[0], &ch, 1);
+            GEventLoop::current().post_event(*piano_widget, make<CCustomEvent>(0));
+            GEventLoop::current().wake();
         }
-    }, piano_widget);
+    },
+        piano_widget);
 
     return app.exec();
 }