Handle multiple keypresses in example (#658)

docs/src/manual/keyevents.md

@@ -29,22 +29,22 @@ and reports the time duration between the two.
 There some state handling here
 because of the likely event
 that your keyboard is set to "repeat" a pressed key
-after some initial delay.
+after some initial delay and because it is possilbe to 
+press multiple keys at once.
 This version reports the time elapsed
 between the _initial_ key press and the key release.
 
 ```julia
 using Gtk
 
-time0 = nothing
+const start_times = Dict{UInt32, UInt32}()
 
 w = GtkWindow("Key Press/Release Example")
 
 id1 = signal_connect(w, "key-press-event") do widget, event
     k = event.keyval
-    global time0
-    if isnothing(time0)
-        time0 = event.time # archive the initial key press time
+    if k ∉ keys(start_times)
+        start_times[k] = event.time # save the initial key press time
         println("You pressed key ", k, " which is '", Char(k), "'.")
     else
         println("repeating key ", k)
@@ -53,8 +53,8 @@ end
 
 id2 = signal_connect(w, "key-release-event") do widget, event
     k = event.keyval
-    duration = event.time - time0 # key press duration in msec
+    start_time = pop!(start_times, k) # remove the key from the dictionary
+    duration = event.time - start_time # key press duration in milliseconds
     println("You released key ", k, " after time ", duration, " msec.")
-    global time0 = nothing # revert to original state for next press
 end
 ```