Adding pool example

examples/pool/.gitignore

@@ -0,0 +1,4 @@
+pool
+pool.exe
+
+*.png

examples/pool/main.go

@@ -0,0 +1,91 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"io/ioutil"
+	"log"
+	"sync"
+	"time"
+
+	cdp "github.com/knq/chromedp"
+	cdptypes "github.com/knq/chromedp/cdp"
+	"github.com/knq/chromedp/cdp/page"
+)
+
+func main() {
+	var err error
+
+	// create context
+	ctxt, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	// create pool
+	pool, err := cdp.NewPool( /*cdp.PoolLog(log.Printf, log.Printf, log.Printf)*/ )
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// loop over the URLs
+	var wg sync.WaitGroup
+	for i, urlstr := range []string{
+		"https://brank.as/",
+		"https://brank.as/careers",
+		"https://brank.as/about",
+	} {
+		wg.Add(1)
+		go takeScreenshot(ctxt, &wg, pool, i, urlstr)
+	}
+
+	// wait for to finish
+	wg.Wait()
+
+	// shutdown pool
+	err = pool.Shutdown()
+	if err != nil {
+		log.Fatal(err)
+	}
+}
+
+func takeScreenshot(ctxt context.Context, wg *sync.WaitGroup, pool *cdp.Pool, id int, urlstr string) {
+	defer wg.Done()
+
+	// allocate
+	c, err := pool.Allocate(ctxt)
+	if err != nil {
+		log.Printf("url (%d) `%s` error: %v", id, urlstr, err)
+		return
+	}
+	defer c.Release()
+
+	// run tasks
+	var buf []byte
+	err = c.Run(ctxt, screenshot(urlstr, &buf))
+	if err != nil {
+		log.Printf("url (%d) `%s` error: %v", id, urlstr, err)
+		return
+	}
+
+	// write to disk
+	err = ioutil.WriteFile(fmt.Sprintf("%d.png", id), buf, 0644)
+	if err != nil {
+		log.Printf("url (%d) `%s` error: %v", id, urlstr, err)
+		return
+	}
+}
+
+func screenshot(urlstr string, picbuf *[]byte) cdp.Action {
+	return cdp.Tasks{
+		cdp.Navigate(urlstr),
+		cdp.Sleep(2 * time.Second),
+		cdp.WaitVisible(`#navbar-nav-main`),
+		cdp.ActionFunc(func(ctxt context.Context, h cdptypes.Handler) error {
+			buf, err := page.CaptureScreenshot().Do(ctxt, h)
+			if err != nil {
+				return err
+			}
+			*picbuf = buf
+			return nil
+		}),
+	}
+}