Merge pull request #98 from mum4k/thread-safe-widgets

Thread safe widgets

CHANGELOG.md

@@ -17,6 +17,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - The LineChart now has an option to change the behavior of the Y axis from
   zero anchored to adaptive.
 - Lint errors reported on the Go report card.
+- Widgets now correctly handle a race when new user data are supplied between
+  calls to their Options() and Draw() methods.
 
 ## [0.5.0] - 21-Jan-2019
 

container/draw.go

@@ -135,8 +135,7 @@ func drawResize(c *Container, area image.Rectangle) error {
 	if err != nil {
 		return err
 	}
-
-	if err := draw.Text(cvs, "⇄", image.Point{0, 0}); err != nil {
+	if err := draw.ResizeNeeded(cvs); err != nil {
 		return err
 	}
 	return cvs.Apply(c.term)

doc/widget_development.md

@@ -10,8 +10,8 @@ callers to set the displayed percentage.
 ## Thread safety
 
 All widget implementations must be thread safe, since the infrastructure calls
-the widget's **Draw()** method concurrently with the user of the widget setting
-the displayed values.
+the widget's **Options** and **Draw()** method concurrently with the user of
+the widget setting the displayed values.
 
 ## Drawing the widget's content
 
@@ -38,12 +38,36 @@ canvas in order to handle under sized or over sized terminals gracefully.
 If the current size of the terminal and the configured container splits result
 in a canvas smaller than the **MinimumSize**, the infrastructure won't call the
 widget's **Draw()** method. The widgets can use this to prevent impossible
-scenarios where an error would have to be returned.
+scenarios where an error would have to be returned. Note that if the values
+returned on a call to the **Options** method aren't static, but depend on the
+user data provided to the widget, the widget **must** protect against the
+scenario where the infrastructure provides a canvas that doesn't match the
+returned options. This is because the infrastructure cannot guarantee the user
+won't change the data between calls to **Options** and **Draw**.
+
+A widget can draw a character indicating that a resize is needed in such cases:
+
+```go
+func (w *Widget) Draw(cvs *canvas.Canvas) error {
+  min := w.minSize() // Output depends on the current state.
+  needAr, err := area.FromSize(min)
+  if err != nil {
+    return err
+  }
+  if !needAr.In(cvs.Area()) {
+    return draw.ResizeNeeded(cvs)
+  }
+
+  // Draw the widget.
+  return nil
+}
+```
 
 If the container configuration results in a canvas larger than **MaximumSize**
 the canvas will be limited to the specified size. Widgets can either specify a
 limit for both the maximum width and height or limit just one of them.
 
+
 ## Unit tests
 
 Unit tests utilize the **faketerm** package which is a fake implementation of a

draw/testdraw/testdraw.go

@@ -65,3 +65,10 @@ func MustBrailleCircle(bc *braille.Canvas, mid image.Point, radius int, opts ...
 		panic(fmt.Sprintf("draw.BrailleCircle => unexpected error: %v", err))
 	}
 }
+
+// MustResizeNeeded draws the character or panics.
+func MustResizeNeeded(cvs *canvas.Canvas) {
+	if err := draw.ResizeNeeded(cvs); err != nil {
+		panic(fmt.Sprintf("draw.ResizeNeeded => unexpected error: %v", err))
+	}
+}

draw/text.go

@@ -187,3 +187,9 @@ func Text(c *canvas.Canvas, text string, start image.Point, opts ...TextOption)
 	}
 	return nil
 }
+
+// ResizeNeeded draws an unicode character indicating that the canvas size is
+// too small to draw meaningful content.
+func ResizeNeeded(cvs *canvas.Canvas) error {
+	return Text(cvs, "⇄", image.Point{0, 0})
+}

draw/text_test.go

@@ -601,3 +601,56 @@ func TestText(t *testing.T) {
 		})
 	}
 }
+
+func TestResizeNeeded(t *testing.T) {
+	tests := []struct {
+		desc   string
+		canvas image.Rectangle
+		want   func(size image.Point) *faketerm.Terminal
+	}{
+		{
+			desc:   "draws the resize needed character",
+			canvas: image.Rect(0, 0, 1, 1),
+			want: func(size image.Point) *faketerm.Terminal {
+				ft := faketerm.MustNew(size)
+				cvs := testcanvas.MustNew(ft.Area())
+				testcanvas.MustSetCell(cvs, image.Point{0, 0}, '⇄')
+				testcanvas.MustApply(cvs, ft)
+				return ft
+			},
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.desc, func(t *testing.T) {
+			cvs, err := canvas.New(tc.canvas)
+			if err != nil {
+				t.Fatalf("canvas.New => unexpected error: %v", err)
+			}
+
+			if err := ResizeNeeded(cvs); err != nil {
+				t.Fatalf("ResizeNeeded => unexpected error: %v", err)
+			}
+
+			got, err := faketerm.New(cvs.Size())
+			if err != nil {
+				t.Fatalf("faketerm.New => unexpected error: %v", err)
+			}
+			if err := cvs.Apply(got); err != nil {
+				t.Fatalf("Apply => unexpected error: %v", err)
+			}
+
+			want, err := faketerm.New(cvs.Size())
+			if err != nil {
+				t.Fatalf("faketerm.New => unexpected error: %v", err)
+			}
+			if tc.want != nil {
+				want = tc.want(cvs.Size())
+			}
+
+			if diff := faketerm.Diff(want, got); diff != "" {
+				t.Errorf("ResizeNeeded => %v", diff)
+			}
+		})
+	}
+}

widgetapi/widgetapi.go

@@ -83,5 +83,13 @@ type Widget interface {
 	// This is how the widget indicates to the infrastructure whether it is
 	// interested in keyboard or mouse shortcuts, what is its minimum canvas
 	// size, etc.
+	//
+	// Most widgets will return statically compiled options (minimum and
+	// maximum size, etc.). If the returned options depend on the runtime state
+	// of the widget (e.g. the user data provided to the widget), the widget
+	// must protect against a case where the infrastructure calls the Draw
+	// method with a canvas that doesn't meet the requested options. This is
+	// because the data in the widget might change between calls to Options and
+	// Draw.
 	Options() Options
 }

widgets/barchart/barchart.go

@@ -23,6 +23,7 @@ import (
 	"sync"
 
 	"github.com/mum4k/termdash/align"
+	"github.com/mum4k/termdash/area"
 	"github.com/mum4k/termdash/canvas"
 	"github.com/mum4k/termdash/cell"
 	"github.com/mum4k/termdash/draw"
@@ -68,6 +69,14 @@ func (bc *BarChart) Draw(cvs *canvas.Canvas) error {
 	bc.mu.Lock()
 	defer bc.mu.Unlock()
 
+	needAr, err := area.FromSize(bc.minSize())
+	if err != nil {
+		return err
+	}
+	if !needAr.In(cvs.Area()) {
+		return draw.ResizeNeeded(cvs)
+	}
+
 	for i, v := range bc.values {
 		r, err := bc.barRect(cvs, i, v)
 		if err != nil {

widgets/barchart/barchart_test.go

@@ -107,6 +107,24 @@ func TestGauge(t *testing.T) {
 			},
 			wantUpdateErr: true,
 		},
+		{
+			desc: "draws resize needed character when canvas is smaller than requested",
+			bc: New(
+				Char('o'),
+			),
+			update: func(bc *BarChart) error {
+				return bc.Values([]int{0, 2, 5, 10}, 10)
+			},
+			canvas: image.Rect(0, 0, 1, 1),
+			want: func(size image.Point) *faketerm.Terminal {
+				ft := faketerm.MustNew(size)
+				c := testcanvas.MustNew(ft.Area())
+
+				testdraw.MustResizeNeeded(c)
+				testcanvas.MustApply(c, ft)
+				return ft
+			},
+		},
 		{
 			desc: "displays bars",
 			bc: New(

widgets/gauge/gauge.go

@@ -249,6 +249,14 @@ func (g *Gauge) Draw(cvs *canvas.Canvas) error {
 	g.mu.Lock()
 	defer g.mu.Unlock()
 
+	needAr, err := area.FromSize(g.minSize())
+	if err != nil {
+		return err
+	}
+	if !needAr.In(cvs.Area()) {
+		return draw.ResizeNeeded(cvs)
+	}
+
 	if g.hasBorder() {
 		if err := draw.Border(cvs, cvs.Area(),
 			draw.BorderLineStyle(g.opts.border),

widgets/gauge/gauge_test.go

@@ -74,6 +74,23 @@ func TestGauge(t *testing.T) {
 				return ft
 			},
 		},
+		{
+			desc: "draws resize needed character when canvas is smaller than requested",
+			gauge: New(
+				Char('o'),
+				Border(draw.LineStyleLight),
+			),
+			percent: &percentCall{p: 35},
+			canvas:  image.Rect(0, 0, 1, 1),
+			want: func(size image.Point) *faketerm.Terminal {
+				ft := faketerm.MustNew(size)
+				c := testcanvas.MustNew(ft.Area())
+
+				testdraw.MustResizeNeeded(c)
+				testcanvas.MustApply(c, ft)
+				return ft
+			},
+		},
 		{
 			desc: "aligns the progress text top and left",
 			gauge: New(

widgets/linechart/linechart.go

@@ -22,6 +22,7 @@ import (
 	"sort"
 	"sync"
 
+	"github.com/mum4k/termdash/area"
 	"github.com/mum4k/termdash/canvas"
 	"github.com/mum4k/termdash/canvas/braille"
 	"github.com/mum4k/termdash/cell"
@@ -173,6 +174,14 @@ func (lc *LineChart) Draw(cvs *canvas.Canvas) error {
 	lc.mu.Lock()
 	defer lc.mu.Unlock()
 
+	needAr, err := area.FromSize(lc.minSize())
+	if err != nil {
+		return err
+	}
+	if !needAr.In(cvs.Area()) {
+		return draw.ResizeNeeded(cvs)
+	}
+
 	yd, err := lc.yAxis.Details(cvs.Area(), lc.opts.yAxisMode)
 	if err != nil {
 		return fmt.Errorf("lc.yAxis.Details => %v", err)
@@ -285,19 +294,24 @@ func (lc *LineChart) Mouse(m *terminalapi.Mouse) error {
 	return errors.New("the LineChart widget doesn't support mouse events")
 }
 
-// Options implements widgetapi.Widget.Options.
-func (lc *LineChart) Options() widgetapi.Options {
-	lc.mu.Lock()
-	defer lc.mu.Unlock()
-
+// minSize determines the minimum required size to draw the line chart.
+func (lc *LineChart) minSize() image.Point {
 	// At the very least we need:
 	// - n cells width for the Y axis and its labels as reported by it.
 	// - at least 1 cell width for the graph.
 	reqWidth := lc.yAxis.RequiredWidth() + 1
 	// - 2 cells height the X axis and its values and 2 for min and max labels on Y.
 	const reqHeight = 4
+	return image.Point{reqWidth, reqHeight}
+}
+
+// Options implements widgetapi.Widget.Options.
+func (lc *LineChart) Options() widgetapi.Options {
+	lc.mu.Lock()
+	defer lc.mu.Unlock()
+
 	return widgetapi.Options{
-		MinimumSize: image.Point{reqWidth, reqHeight},
+		MinimumSize: lc.minSize(),
 	}
 }
 

widgets/linechart/linechart_test.go

@@ -64,14 +64,16 @@ func TestLineChartDraws(t *testing.T) {
 			wantWriteErr: true,
 		},
 		{
-			desc:    "draw fails when canvas not wide enough",
-			canvas:  image.Rect(0, 0, 2, 4),
-			wantErr: true,
-		},
-		{
-			desc:    "draw fails when canvas not tall enough",
-			canvas:  image.Rect(0, 0, 3, 3),
-			wantErr: true,
+			desc:   "draws resize needed character when canvas is smaller than requested",
+			canvas: image.Rect(0, 0, 1, 1),
+			want: func(size image.Point) *faketerm.Terminal {
+				ft := faketerm.MustNew(size)
+				c := testcanvas.MustNew(ft.Area())
+
+				testdraw.MustResizeNeeded(c)
+				testcanvas.MustApply(c, ft)
+				return ft
+			},
 		},
 		{
 			desc:   "empty without series",

widgets/sparkline/sparkline.go

@@ -21,6 +21,7 @@ import (
 	"image"
 	"sync"
 
+	"github.com/mum4k/termdash/area"
 	"github.com/mum4k/termdash/canvas"
 	"github.com/mum4k/termdash/cell"
 	"github.com/mum4k/termdash/draw"
@@ -62,6 +63,14 @@ func (sl *SparkLine) Draw(cvs *canvas.Canvas) error {
 	sl.mu.Lock()
 	defer sl.mu.Unlock()
 
+	needAr, err := area.FromSize(sl.minSize())
+	if err != nil {
+		return err
+	}
+	if !needAr.In(cvs.Area()) {
+		return draw.ResizeNeeded(cvs)
+	}
+
 	ar := sl.area(cvs)
 	visible, max := visibleMax(sl.data, ar.Dx())
 	var curX int

widgets/sparkline/sparkline_test.go

@@ -291,6 +291,24 @@ func TestSparkLine(t *testing.T) {
 				return ft
 			},
 		},
+		{
+			desc: "draws resize needed character when canvas is smaller than requested",
+			sparkLine: New(
+				Height(2),
+			),
+			update: func(sl *SparkLine) error {
+				return sl.Add([]int{0, 100, 50, 85})
+			},
+			canvas: image.Rect(0, 0, 1, 1),
+			want: func(size image.Point) *faketerm.Terminal {
+				ft := faketerm.MustNew(size)
+				c := testcanvas.MustNew(ft.Area())
+
+				testdraw.MustResizeNeeded(c)
+				testcanvas.MustApply(c, ft)
+				return ft
+			},
+		},
 		{
 			desc: "respects fixed height with label",
 			sparkLine: New(