Add a background-running simulation example

Issue #32

example/progressbar.jl

@@ -0,0 +1,53 @@
+# This example show how to update the GUI dusing a long-running simulation
+
+using Base.Test
+using QML
+
+qmlfile = joinpath(dirname(Base.source_path()), "qml", "progressbar.qml")
+
+type SimulationState
+  progress::Float64
+end
+
+const simulation_state = SimulationState(0.0)
+
+# Our simulation is just a busy wait, producing progress between 0.0 and 1.0
+function simulate()
+  counter = 0.0
+  maxcount = 1000000000.0
+  while counter < maxcount
+    for i in 1:Int(maxcount/10)
+      counter += 1.0
+    end
+    produce(counter/maxcount)
+  end
+  produce(1.0)
+end
+
+simulation_task = Task(simulate)
+
+# Run a step in the simulation, restart if already finished
+function step()
+  global simulation_state
+  global simulation_task
+
+  if simulation_state.progress >= 1.0
+    println("Simulation was finished, restarting")
+    simulation_task = Task(simulate)
+  end
+
+  @show progress = consume(simulation_task)
+  @qmlset qmlcontext().simulation_state.progress = progress
+
+  return
+end
+
+# Register the stepping function function
+@qmlfunction step
+
+# The timer will run simulation steps as fast as it can while active, yielding to the GUI after each tick
+timer = QTimer()
+
+# All arguments after qmlfile are context properties:
+@qmlapp qmlfile simulation_state timer
+exec()

example/qml/progressbar.qml

@@ -0,0 +1,43 @@
+import QtQuick 2.0
+import QtQuick.Controls 1.0
+import QtQuick.Layouts 1.0
+import org.julialang 1.0
+
+ApplicationWindow {
+  title: "My Application"
+  width: 480
+  height: 200
+  visible: true
+
+  // Set up timer connection
+  Connections {
+    target: timer
+    onTimeout: Julia.step()
+  }
+
+  ColumnLayout {
+    spacing: 6
+    anchors.centerIn: parent
+
+    ProgressBar {
+      value: simulation_state.progress
+      onValueChanged: {
+        if(value >= 1.0) {
+          timer.stop()
+        }
+      }
+    }
+
+    Button {
+      Layout.alignment: Qt.AlignCenter
+      text: "Start simulation"
+      onClicked: timer.start()
+    }
+
+    Button {
+      Layout.alignment: Qt.AlignCenter
+      text: "Stop simulation"
+      onClicked: timer.stop()
+    }
+  }
+}