go: example of waitgroup usage with aggregation of results

golang/waitgroup.go

@@ -0,0 +1,64 @@
+package main
+
+import (
+	"fmt"
+	"math"
+	"sync"
+)
+
+// worker is an example of worker that count x^2 and put it into receiving-only channel
+func worker(input float64, resultChan chan<- float64) {
+	// return input^2
+	resultChan <- math.Pow(input, 2)
+}
+
+// This example will wait for result being processed before calling waitgroup.Done() to ensure not only that
+// all worker is done, but also result of the work has been processed in the case that
+// aggregation of results are needed
+func main() {
+	var wg sync.WaitGroup
+	// Define the work array
+	workQueue := []float64{20, 40, 60, 80, 100}
+
+	// Add count of work to be done to work group (not considering upper bound, etc)
+	workCount := len(workQueue)
+	wg.Add(workCount)
+
+	// Define buffered result channel with size of work count
+	resultChan := make(chan float64, workCount)
+	defer close(resultChan)
+
+	// Define a done channel
+	done := make(chan bool, 1)
+	defer close(done)
+
+	// Spawn a wait in a separate routine to monitor for completion of wait group
+	go func() {
+		wg.Wait()
+		done <- true
+	}()
+
+	// Loop through and spawn off workers
+	for _, work := range workQueue {
+		go worker(work, resultChan)
+	}
+
+	// Wait for result channel to receive all expected results and exit
+	var currentTotal float64
+
+	for {
+		select {
+		case result := <-resultChan:
+			// select case to receive results
+			newTotal := currentTotal + result
+			fmt.Printf("Result received: %f [total= %f + %f = %f]\n", result, currentTotal, result, newTotal)
+			currentTotal = newTotal
+			// indicate that a result has been processed/aggregated
+			wg.Done()
+		case <-done:
+			// select case that all result is done (see line 35 where done bool is sent)
+			fmt.Printf("All results has been received total is %f, now exitting...\n", currentTotal)
+			return
+		}
+	}
+}