From ff55e2f0551d6d392edb5302c27a1f6cc88b5082 Mon Sep 17 00:00:00 2001
From: Julian Ospald <hasufell@posteo.de>
Date: Sat, 7 Oct 2017 16:42:20 +0200
Subject: [PATCH] Get rid of wait groups

---
 src/numbers/numbers.go | 31 +++++++++++++------------------
 1 file changed, 13 insertions(+), 18 deletions(-)

diff --git a/src/numbers/numbers.go b/src/numbers/numbers.go
index eb5471f..c41fc4e 100644
--- a/src/numbers/numbers.go
+++ b/src/numbers/numbers.go
@@ -10,7 +10,6 @@ import (
 	"net/http"
 	"net/url"
 	"numbers/sort"
-	"sync"
 	"time"
 )
 
@@ -64,13 +63,10 @@ func numbersHandler(w http.ResponseWriter, r *http.Request) {
 
 	// Non-blocking channel for sorted results
 	sortChan := make(chan []int, len(rurl))
-	var wg sync.WaitGroup
 
 	// fetch all URLs asynchronously and sort them
 	for i := range rurl {
-		wg.Add(1)
 		go func(url string) {
-			defer wg.Done()
 			n, e := getNumbers(url, ctx)
 
 			if e == nil { // we have a usable JSON list of numbers
@@ -89,30 +85,29 @@ func numbersHandler(w http.ResponseWriter, r *http.Request) {
 			}
 		}(rurl[i])
 	}
-	// master routine closing the inputChan
-	go func() {
-		wg.Wait()
-		close(sortChan)
-	}()
 
 	// result list that is returned on short-circuit
 	var resultList []int = []int{}
 
+	// counter of how many merge operations have been performed
+	mc := 0
+
 	// get all sorted lists concurrently and merge them as we go
-	done := false
-	for done != true {
+Outer:
+	for {
 		select {
 		case <-ctx.Done():
 			log.Printf("Waiting for URL took too long, finishing response anyway")
 			finishResponse(w, resultList)
 			return
-		case res, more := <-sortChan:
-			if more {
-				merged := sort.MergeLists(resultList, res)
-				resultList = merged
-			} else {
-				log.Printf("Nothing else to sort")
-				done = true
+		case res := <-sortChan:
+			merged := sort.MergeLists(resultList, res)
+			resultList = merged
+			mc += 1
+			// if we have len(rurl) merge operations, then
+			// all lists have been processed already
+			if mc >= len(rurl) {
+				break Outer
 			}
 		}
 	}