LibGUI: Implement nested event loops to support dialog boxes.

This patch adds a simple GMessageBox that can run in a nested event loop.
Here's how you use it:

    GMessageBox box("Message text here", "Message window title");
    int result = box.exec();

The next step is to make the WindowServer respect the modality flag of
these windows and prevent interaction with other windows in the same
process until the modal window has been closed.

1 files changed, 18 insertions, 5 deletions

diff --git a/LibGUI/GObject.cpp b/LibGUI/GObject.cpp
index 1d2c59b427..4dbbe4bc0b 100644
--- a/LibGUI/GObject.cpp
+++ b/LibGUI/GObject.cpp
@@ -2,6 +2,7 @@
 #include "GEvent.h"
 #include "GEventLoop.h"
 #include <AK/Assertions.h>
+#include <stdio.h>
 
 GObject::GObject(GObject* parent)
     : m_parent(parent)
@@ -42,7 +43,7 @@ void GObject::event(GEvent& event)
 void GObject::add_child(GObject& object)
 {
     m_children.append(&object);
-    GEventLoop::main().post_event(*this, make<GChildEvent>(GEvent::ChildAdded, object));
+    GEventLoop::current().post_event(*this, make<GChildEvent>(GEvent::ChildAdded, object));
 }
 
 void GObject::remove_child(GObject& object)
@@ -50,7 +51,7 @@ void GObject::remove_child(GObject& object)
     for (ssize_t i = 0; i < m_children.size(); ++i) {
         if (m_children[i] == &object) {
             m_children.remove(i);
-            GEventLoop::main().post_event(*this, make<GChildEvent>(GEvent::ChildRemoved, object));
+            GEventLoop::current().post_event(*this, make<GChildEvent>(GEvent::ChildRemoved, object));
             return;
         }
     }
@@ -71,20 +72,32 @@ void GObject::start_timer(int ms)
         ASSERT_NOT_REACHED();
     }
 
-    m_timer_id = GEventLoop::main().register_timer(*this, ms, true);
+    m_timer_id = GEventLoop::register_timer(*this, ms, true);
 }
 
 void GObject::stop_timer()
 {
     if (!m_timer_id)
         return;
-    bool success = GEventLoop::main().unregister_timer(m_timer_id);
+    bool success = GEventLoop::unregister_timer(m_timer_id);
     ASSERT(success);
     m_timer_id = 0;
 }
 
 void GObject::delete_later()
 {
-    GEventLoop::main().post_event(*this, make<GEvent>(GEvent::DeferredDestroy));
+    GEventLoop::current().post_event(*this, make<GEvent>(GEvent::DeferredDestroy));
 }
 
+void GObject::dump_tree(int indent)
+{
+    for (int i = 0; i < indent; ++i) {
+        printf(" ");
+    }
+    printf("%s{%p}\n", class_name(), this);
+
+    for (auto* child : children()) {
+        child->dump_tree(indent + 2);
+    }
+
+}