content: add untimate-channel

content/assets/ultimate-channel/chan.go

@@ -0,0 +1,42 @@
+// Copyright 2021 The golang.design Initiative Authors.
+// All rights reserved. Use of this source code is governed
+// by a MIT license that can be found in the LICENSE file.
+//
+// Written by Changkun Ou <changkun.de>
+
+package main
+
+// MakeChan returns a sender and a receiver of a buffered channel
+// with infinite capacity.
+func MakeChan() (chan<- interface{}, <-chan interface{}) {
+	in, out := make(chan interface{}), make(chan interface{})
+
+	go func() {
+		var q []interface{}
+		for {
+			e, ok := <-in
+			if !ok {
+				close(out)
+				return
+			}
+			q = append(q, e)
+			for len(q) > 0 {
+				select {
+				case out <- q[0]:
+					q = q[1:]
+				case e, ok := <-in:
+					if ok {
+						q = append(q, e)
+						break
+					}
+					for _, e := range q {
+						out <- e
+					}
+					close(out)
+					return
+				}
+			}
+		}
+	}()
+	return in, out
+}

content/assets/ultimate-channel/go.mod

@@ -0,0 +1,3 @@
+module deadlock-drawcall
+
+go 1.17

content/assets/ultimate-channel/main.go

@@ -0,0 +1,92 @@
+// Copyright 2021 The golang.design Initiative Authors.
+// All rights reserved. Use of this source code is governed
+// by a MIT license that can be found in the LICENSE file.
+//
+// Written by Changkun Ou <changkun.de>
+
+// WARNING: This example contains a deadlock.
+package main
+
+import (
+	"fmt"
+	"math/rand"
+	"time"
+)
+
+type ResizeEvent struct {
+	width, height int
+}
+
+type renderProfile struct {
+	id     int
+	width  int
+	height int
+}
+
+// Draw executes a draw call by the given render profile
+func (p *renderProfile) Draw() interface{} {
+	return fmt.Sprintf("draw-%d-%dx%d", p.id, p.width, p.height)
+}
+
+func main() {
+	// draw is a channel for receiving finished draw calls.
+	draw := make(chan interface{})
+
+	// Solution 2 (step 1):
+	// drawIn, drawOut := MakeChan()
+
+	// change is a channel to receive notification of the change of
+	// rendering settings.
+	change := make(chan ResizeEvent)
+
+	// Rendering Thread
+	//
+	// Sending drawcalls to the event thread in order to draw pictures.
+	// The thread sends darwcalls to the draw channel, using the same
+	// rendering setting id. If there is a change of rendering setting,
+	// the event thread notifies the rendering setting change, and here
+	// increases the rendering setting id.
+	go func() {
+		p := &renderProfile{id: 0, width: 800, height: 500}
+		for {
+			select {
+			case size := <-change:
+				// Modify rendering profile.
+				p.id++
+				p.width = size.width
+				p.height = size.height
+			default:
+				draw <- p.Draw()
+				// Solution 1:
+				// select {
+				// case draw <- p.Draw():
+				// default:
+				// }
+				// Solution 2 (step 2):
+				// drawIn <- p.Draw()
+			}
+		}
+	}()
+
+	// Event Thread
+	//
+	// Process events every 100 ms. Otherwise, process drawcall request
+	// upon-avaliable.
+	event := time.NewTicker(100 * time.Millisecond)
+	for {
+		select {
+		case id := <-draw:
+			// Solution 2 (step 3):
+			// case id := <-drawOut:
+			println(id)
+		case <-event.C:
+			// Notify the rendering thread there is a change regarding
+			// rendering settings. We simulate a random size at every
+			// event processing loop.
+			change <- ResizeEvent{
+				width:  int(rand.Float64() * 100),
+				height: int(rand.Float64() * 100),
+			}
+		}
+	}
+}