LibCore: Add Notifier::close

If a file descriptor is being closed, we need to permanently disable
any Notifier and remove it from the event loop. This method removes
the notifier and disables it so that the EventLoop does not use a
invalid file descriptor.

Libraries/LibCore/Notifier.cpp

@@ -46,12 +46,22 @@ Notifier::~Notifier()
 
 void Notifier::set_enabled(bool enabled)
 {
+    if (m_fd < 0)
+        return;
     if (enabled)
         Core::EventLoop::register_notifier({}, *this);
     else
         Core::EventLoop::unregister_notifier({}, *this);
 }
 
+void Notifier::close()
+{
+    if (m_fd < 0)
+        return;
+    set_enabled(false);
+    m_fd = -1;
+}
+
 void Notifier::event(Core::Event& event)
 {
     if (event.type() == Core::Event::NotifierRead && on_ready_to_read) {

Libraries/LibCore/Notifier.h

@@ -48,6 +48,8 @@ public:
     Function<void()> on_ready_to_read;
     Function<void()> on_ready_to_write;
 
+    void close();
+
     int fd() const { return m_fd; }
     unsigned event_mask() const { return m_event_mask; }
     void set_event_mask(unsigned event_mask) { m_event_mask = event_mask; }