From 5e10c8f5833bf2e15caa69fa3fb12f5090d49fc7 Mon Sep 17 00:00:00 2001
From: "Stephen McQuay (smcquay)" <stephen@mcquay.me>
Date: Tue, 15 Nov 2016 20:50:04 -0800
Subject: [PATCH] parallel hashing

---
 check.go | 162 ++++++++++++++++++++++++++++++++++++-------------------
 main.go  |   6 ++-
 2 files changed, 112 insertions(+), 56 deletions(-)

diff --git a/check.go b/check.go
index 4e067e9..7820a39 100644
--- a/check.go
+++ b/check.go
@@ -6,13 +6,13 @@ import (
 	"crypto/sha1"
 	"crypto/sha256"
 	"crypto/sha512"
-	"errors"
 	"fmt"
 	"hash"
 	"io"
 	"log"
 	"os"
 	"strings"
+	"sync"
 )
 
 type checksum struct {
@@ -43,61 +43,113 @@ func parseCS(line string) (checksum, error) {
 	return checksum{filename: f, hash: hsh, checksum: cs}, nil
 }
 
-func check(files []string) error {
-	streams := []io.ReadCloser{}
-	defer func() {
-		for _, stream := range streams {
-			stream.Close()
+type input struct {
+	f   io.ReadCloser
+	err error
+}
+
+type work struct {
+	cs  checksum
+	err error
+}
+
+func streams(files []string) chan input {
+	r := make(chan input)
+
+	go func() {
+		for _, name := range files {
+			f, err := os.Open(name)
+			r <- input{f, err}
 		}
+		if len(files) == 0 {
+			r <- input{f: os.Stdin}
+		}
+		close(r)
 	}()
 
-	for _, name := range files {
-		f, err := os.Open(name)
-		if err != nil {
-			return err
-		}
-		streams = append(streams, f)
-	}
-	if len(files) == 0 {
-		streams = append(streams, os.Stdin)
-	}
-
-	jobs := []checksum{}
-	for _, stream := range streams {
-		s := bufio.NewScanner(stream)
-		for s.Scan() {
-			cs, err := parseCS(s.Text())
-			if err != nil {
-				return err
-			}
-			jobs = append(jobs, cs)
-		}
-		if s.Err() != nil {
-			return s.Err()
-		}
-	}
-
-	errs := 0
-	for _, job := range jobs {
-		f, err := os.Open(job.filename)
-		if err != nil {
-			return fmt.Errorf("open: %v", err)
-		}
-		if _, err := io.Copy(job.hash, f); err != nil {
-			log.Printf("%+v", err)
-		}
-		f.Close()
-		if fmt.Sprintf("%x", job.hash.Sum(nil)) == job.checksum {
-			fmt.Printf("%s: OK\n", job.filename)
-		} else {
-			errs++
-			fmt.Fprintf(os.Stderr, "%s: bad\n", job.filename)
-		}
-	}
-
-	var err error
-	if errs != 0 {
-		err = errors.New("bad files found")
-	}
-	return err
+	return r
+}
+
+func check(files []string) chan error {
+	jobs := make(chan work)
+
+	go func() {
+		for stream := range streams(files) {
+			if stream.err != nil {
+				jobs <- work{err: stream.err}
+				break
+			}
+			s := bufio.NewScanner(stream.f)
+			for s.Scan() {
+				cs, err := parseCS(s.Text())
+				jobs <- work{cs, err}
+			}
+			stream.f.Close()
+			if s.Err() != nil {
+				jobs <- work{err: s.Err()}
+			}
+		}
+		close(jobs)
+	}()
+
+	results := []<-chan error{}
+
+	workers := 8
+	for w := 0; w < workers; w++ {
+		results = append(results, compute(jobs))
+	}
+
+	return merge(results)
+}
+
+func merge(cs []<-chan error) chan error {
+	out := make(chan error)
+
+	var wg sync.WaitGroup
+
+	output := func(c <-chan error) {
+		for n := range c {
+			out <- n
+		}
+		wg.Done()
+	}
+
+	wg.Add(len(cs))
+	for _, c := range cs {
+		go output(c)
+	}
+
+	go func() {
+		wg.Wait()
+		close(out)
+	}()
+	return out
+}
+
+func compute(jobs chan work) chan error {
+	r := make(chan error)
+	go func() {
+		for job := range jobs {
+			if job.err != nil {
+				log.Printf("%+v", job.err)
+				continue
+			}
+			f, err := os.Open(job.cs.filename)
+			if err != nil {
+				r <- fmt.Errorf("open: %v", err)
+				continue
+			}
+			if _, err := io.Copy(job.cs.hash, f); err != nil {
+				log.Printf("%+v", err)
+			}
+			f.Close()
+			if fmt.Sprintf("%x", job.cs.hash.Sum(nil)) == job.cs.checksum {
+				fmt.Printf("%s: OK\n", job.cs.filename)
+			} else {
+				r <- fmt.Errorf("%s: bad", job.cs.filename)
+			}
+		}
+		close(r)
+	}()
+	return r
 }
diff --git a/main.go b/main.go
index cd2de4d..c261dd5 100644
--- a/main.go
+++ b/main.go
@@ -19,8 +19,12 @@ func main() {
 	files := flag.Args()
 	switch *mode {
 	case true:
-		if err := check(files); err != nil {
+		c := 0
+		for err := range check(files) {
+			c++
 			fmt.Fprintf(os.Stderr, "%v\n", err)
+		}
+		if c > 0 {
 			os.Exit(1)
 		}
 	case false: