From 8b70410d5848258cc2e86e7eec0504b46b48f27d Mon Sep 17 00:00:00 2001
From: Greg <gmp@wow.st>
Date: Thu, 2 Apr 2020 14:06:11 -0400
Subject: [PATCH] Add concurrency.

---
 main.go | 52 ++++++++++++++++++++++++++++++++--------------------
 1 file changed, 32 insertions(+), 20 deletions(-)

diff --git a/main.go b/main.go
index c924014..80d9afd 100644
--- a/main.go
+++ b/main.go
@@ -6,41 +6,53 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"sync"
 
 	"github.com/zeebo/blake3"
 )
 
 var (
 	help = flag.Bool("h", false, "Prints help information")
-	length = flag.Int("l", 32,  "The number of output bytes, prior to hex encoding (default 32)")
+	length = flag.Int("l", 32,  "The number of output bytes, prior to hex encoding")
+	par = flag.Int("p", 4, "The maximum concurrency")
 )
 
 func main() {
 	flag.Parse()
-	if *help || len(flag.Args()) == 0 {
+	if *help || len(flag.Args()) == 0 || *par < 1 {
 		flag.Usage()
 		os.Exit(0)
 	}
-	buf := [65536]byte{}
+	q := make(chan struct{}, *par)
+	wg := &sync.WaitGroup{}
+
 	for _, name := range flag.Args() {
-		file, err := os.Open(name)
-		if err != nil {
-			panic(err)
-		}
-		hasher := blake3.NewSized(*length)
-		for {
-			n, err := file.Read(buf[:])
-			hasher.Write(buf[:n])
-			if err == io.EOF {
-				break
-			} else if err != nil {
+		q <- struct{}{}
+		wg.Add(1)
+		go func(name string) {
+			buf := [65536]byte{}
+			file, err := os.Open(name)
+			if err != nil {
 				panic(err)
 			}
-		}
-		file.Close()
-		hash := hasher.Sum([]byte{})
-		fmt.Print(hex.EncodeToString(hash))
-		fmt.Print("  ")
-		fmt.Println(name)
+			hasher := blake3.NewSized(*length)
+			for {
+				n, err := file.Read(buf[:])
+				hasher.Write(buf[:n])
+				if err == io.EOF {
+					break
+				} else if err != nil {
+					panic(err)
+				}
+			}
+			file.Close()
+			hash := hasher.Sum([]byte{})
+			fmt.Print(hex.EncodeToString(hash))
+			fmt.Print("  ")
+			fmt.Println(name)
+			<- q
+			wg.Done()
+		}(name)
 	}
+	wg.Wait()
 }