[ERRGROUPS] adds errgroup example

examples/channels/errgroups/errgroups.go

@@ -0,0 +1,52 @@
+package main
+
+import (
+	"fmt"
+	"golang.org/x/sync/errgroup"
+	"log"
+)
+
+// START OMIT
+func sum(nums []int, resultChannel chan<- int) {
+	total := 0
+	for _, v := range nums {
+		total += v
+	}
+	resultChannel <- total
+}
+
+func doit() error {
+	var g errgroup.Group
+	resultChannel := make(chan int, 2)
+
+	numSets := [][]int{{1, 2, 3}, {4, 5, 6}}
+
+	for _, nums := range numSets {
+		nums := nums // no longer needed after 1.23
+		g.Go(func() error {
+			sum(nums, resultChannel)
+			return nil
+		})
+	}
+	// First error will cancel all pending go routines
+	if err := g.Wait(); err != nil {
+		return err
+	}
+	close(resultChannel)
+
+	totalSum := 0
+	for result := range resultChannel {
+		totalSum += result
+	}
+	fmt.Printf("sum=%d\n", totalSum)
+	return nil
+}
+
+// END OMIT
+
+func main() {
+	err := doit()
+	if err != nil {
+		log.Fatal(err)
+	}
+}

go-training.slide

@@ -1536,6 +1536,12 @@ Alternative approaches:
 
 #----------------------------------------------
 
+* Divide the work <channels + errgroup>
+
+.play -edit examples/channels/errgroups/errgroups.go /START OMIT/,/END OMIT/
+
+#----------------------------------------------
+
 * Select example <select>
 - Wait for events on multiple channels