Mandelbrot snippets from github.com/campoy/mandelbrot, for a post on blog.campoy.cat

parallel.go

func fillImg(m *img) {
	// init a WaitGroup with the number of pixels of the image
	var wg sync.WaitGroup
	wg.Add(m.h * m.w)
	
	for i, row := range m.m {
		for j := range row {
			// Every pixel is computed in a different goroutine
			// and the counter is decreased once it's done.
			go func(i, j int) {
				fillPixel(m, i, j)
				wg.Done()
			}(i, j)
		}
	}
	wg.Wait()
}

sequential.go

func fillImg(m *img) {
	for i, row := range m.m {
		for j := range row {
			fillPixel(m, i, j)
		}
	}
}

workers.go

func fillImg(m *img) {
	// Channel of pixels, or tasks if you prefer.
	c := make(chan struct{ i, j int })

	// We start nWorkers reading from the channel.
	// When the channel is closed they all exit.
	for i := 0; i < nWorkers; i++ {
		go func() {
			for t := range c {
				fillPixel(m, t.i, t.j)
			}
		}()
	}

	// Then we send every pixel into the channel
	for i, row := range m.m {
		for j := range row {
			c <- struct{ i, j int }{i, j}
		}
	}
	
	// At the end we close the channel so all goroutines exit.
	close(c)
}