Automatic event loop start/stop when not showing anything (#607)

* add idle and isidle for controlling event loop idle state

* start idle by default but expose ENV var to change default

* unset idle with any call to `show` or `showall`

* automatically return to idle when shown widgets are destroyed

* tidy up

* start/stop the gtk eventloop instead

* only start eventloop when widget is actually going to be drawn

src/GLib/GLib.jl

@@ -41,6 +41,8 @@ cfunction_(@nospecialize(f), r, a::Tuple) = cfunction_(f, r, Tuple{a...})
     end
 end
 
+const gtk_eventloop_f = Ref{Function}()
+
 # local function, handles Symbol and makes UTF8-strings easier
 const  AbstractStringLike = Union{AbstractString, Symbol}
 bytestring(s) = String(s)

src/GLib/signals.jl

@@ -381,6 +381,7 @@ end
 @deprecate g_timeout_add(interval, cb, user_data) g_timeout_add(() -> cb(user_data), interval)
 
 function g_idle_add(cb::Function)
+    gtk_eventloop_f[](true)
     callback = @cfunction(_g_callback, Cint, (Ref{Function},))
     ref, deref = gc_ref_closure(cb)
     return ccall((:g_idle_add_full , libglib),Cint,

src/Gtk.jl

@@ -128,13 +128,50 @@ function __init__()
             C_NULL, C_NULL, "Julia Gtk Bindings", C_NULL, C_NULL, error_check)
     end
 
-    # if g_main_depth > 0, a glib main-loop is already running,
-    # so we don't need to start a new one
-    if ccall((:g_main_depth, GLib.libglib), Cint, ()) == 0
-        global gtk_main_task = schedule(Task(gtk_main))
+    # if g_main_depth > 0, a glib main-loop is already running.
+    # unfortunately this call does not reliably reflect the state after the
+    # loop has been stopped or restarted, so only use it once at the start
+    gtk_main_running[] = ccall((:g_main_depth, GLib.libglib), Cint, ()) > 0
+
+    # Given GLib provides `g_idle_add` to specify what happens during idle, this allows
+    # that call to also start the eventloop
+    GLib.gtk_eventloop_f[] = enable_eventloop
+
+    auto_idle[] = get(ENV, "GTK_AUTO_IDLE", "true") == "true"
+
+    # by default, defer starting the event loop until either `show`, `showall`, or `g_idle_add` is called
+    enable_eventloop(!auto_idle[])
+end
+
+const auto_idle = Ref{Bool}(true) # control default via ENV["GTK_AUTO_IDLE"]
+const gtk_main_running = Ref{Bool}(false)
+
+"""
+    Gtk.enable_eventloop(b::Bool = true)
+
+Set whether Gtk's event loop is running.
+"""
+function enable_eventloop(b::Bool = true)
+    if b
+        if !is_eventloop_running()
+            global gtk_main_task = schedule(Task(gtk_main))
+            gtk_main_running[] = true
+        end
+    else
+        if is_eventloop_running()
+            gtk_quit()
+            gtk_main_running[] = false
+        end
     end
 end
 
+"""
+    Gtk.is_eventloop_running()::Bool
+
+Check whether Gtk's event loop is running.
+"""
+is_eventloop_running() = gtk_main_running[]
+
 const ser_version = Serialization.ser_version
 let cachedir = joinpath(splitdir(@__FILE__)[1], "..", "gen")
     fastgtkcache = joinpath(cachedir, "gtk$(libgtk_version.major)_julia_ser$(ser_version)")

src/base.jl

@@ -27,8 +27,31 @@ screen_size(w::GtkWindowLeaf) = screen_size(Gtk.GAccessor.screen(w))
 ### Functions and methods common to all GtkWidget objects
 visible(w::GtkWidget) = Bool(ccall((:gtk_widget_get_visible, libgtk), Cint, (Ptr{GObject},), w))
 visible(w::GtkWidget, state::Bool) = @sigatom ccall((:gtk_widget_set_visible, libgtk), Nothing, (Ptr{GObject}, Cint), w, state)
-show(w::GtkWidget) = (@sigatom ccall((:gtk_widget_show, libgtk), Nothing, (Ptr{GObject},), w); w)
-showall(w::GtkWidget) = (@sigatom ccall((:gtk_widget_show_all, libgtk), Nothing, (Ptr{GObject},), w); w)
+
+const shown_widgets = WeakKeyDict()
+function handle_auto_idle(w::GtkWidget)
+    if auto_idle[]
+        signal_connect(w, :realize) do w
+            enable_eventloop(true)
+            shown_widgets[w] = nothing
+            signal_connect(w, :destroy) do w
+                delete!(shown_widgets, w)
+                isempty(shown_widgets) && enable_eventloop(false)
+            end
+        end
+    end
+end
+function show(w::GtkWidget)
+    handle_auto_idle(w)
+    @sigatom ccall((:gtk_widget_show, libgtk), Nothing, (Ptr{GObject},), w)
+    w
+end
+function showall(w::GtkWidget)
+    handle_auto_idle(w)
+    @sigatom ccall((:gtk_widget_show_all, libgtk), Nothing, (Ptr{GObject},), w)
+    w
+end
+
 hide(w::GtkWidget) = (@sigatom ccall((:gtk_widget_hide , libgtk),Cvoid,(Ptr{GObject},),w); w)
 grab_focus(w::GtkWidget) = (@sigatom ccall((:gtk_widget_grab_focus , libgtk), Cvoid, (Ptr{GObject},), w); w)
 

src/windows.jl

@@ -17,9 +17,9 @@ end
 
 resize!(win::GtkWindow, w::Integer, h::Integer) = ccall((:gtk_window_resize, libgtk), Nothing, (Ptr{GObject}, Int32, Int32), win, w, h)
 
-present(win::GtkWindow) = ccall((:gtk_window_present, libgtk), Nothing, (Ptr{GObject},), win)
+present(win::GtkWindow) = (handle_auto_idle(win); ccall((:gtk_window_present, libgtk), Nothing, (Ptr{GObject},), win))
 
-fullscreen(win::GtkWindow) = ccall((:gtk_window_fullscreen, libgtk), Nothing, (Ptr{GObject},), win)
+fullscreen(win::GtkWindow) = (handle_auto_idle(win); ccall((:gtk_window_fullscreen, libgtk), Nothing, (Ptr{GObject},), win))
 unfullscreen(win::GtkWindow) = ccall((:gtk_window_unfullscreen, libgtk), Nothing, (Ptr{GObject},), win)
 
 maximize(win::GtkWindow) = ccall((:gtk_window_maximize, libgtk), Nothing, (Ptr{GObject},), win)