init

.gitignore

@@ -0,0 +1,3 @@
+.idea
+*.out
+100-go-mistakes.iml

README.md

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+go test -bench=. -trace trace.out
+go tool trace trace.out

concurrency/concurrency-not-magic.go

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+package concurrency
+
+import (
+	"bufio"
+	"io"
+	"runtime"
+	"strconv"
+	"strings"
+	"sync"
+	"time"
+)
+
+type customer struct {
+	id        string
+	firstName string
+	lastName  string
+	ts        time.Time
+}
+
+func parseFile(reader *bufio.Reader) ([]customer, error) {
+	customers := make([]customer, 0)
+	for {
+		// Read a line
+		line, _, err := reader.ReadLine()
+		if err != nil {
+			switch err {
+			default:
+				return nil, err
+			case io.EOF:
+				// If io.EOF, we reached the end of the input
+				return customers, nil
+			}
+		}
+		// Call parseLine and another customer
+		customers = append(customers, parseLine(string(line)))
+	}
+	return customers, nil
+}
+
+func parseLine(line string) customer {
+	tokens := strings.Split(line, ",")
+	ts, _ := strconv.ParseInt(tokens[3], 10, 64)
+	return customer{
+		id:        tokens[0],
+		firstName: tokens[1],
+		lastName:  tokens[2],
+		ts:        time.Unix(ts, 0),
+	}
+}
+
+func parseFileWorker(reader *bufio.Reader) ([]customer, error) {
+	inputs := make(chan string, 1024)
+	results := make(chan customer, 1024)
+	customers := make([]customer, 0)
+
+	// Spin up multiple worker goroutines
+	workerWg := sync.WaitGroup{}
+	for i := 0; i < runtime.NumCPU(); i++ {
+		workerWg.Add(1)
+		go parseLineWorker(&workerWg, inputs, results)
+	}
+
+	// Gather
+	gatherWg := sync.WaitGroup{}
+	gatherWg.Add(1)
+	go func() {
+		for customer := range results {
+			customers = append(customers, customer)
+		}
+		gatherWg.Done()
+	}()
+
+	// When workers are complete, we close the channel.
+	go func() {
+		workerWg.Wait()
+		close(results)
+	}()
+
+loop:
+	for {
+		line, _, err := reader.ReadLine()
+		if err != nil {
+			switch err {
+			default:
+				return nil, err
+			case io.EOF:
+				break loop
+			}
+		}
+		// Scatter
+		inputs <- string(line)
+	}
+	close(inputs)
+
+	// Wait for the gather goroutine to complete.
+	gatherWg.Wait()
+	return customers, nil
+}
+
+func parseLineWorker(wg *sync.WaitGroup, input <-chan string, output chan<- customer) {
+	for line := range input {
+		tokens := strings.Split(line, ",")
+		ts, _ := strconv.ParseInt(tokens[3], 10, 64)
+		output <- customer{
+			id:        tokens[0],
+			firstName: tokens[1],
+			lastName:  tokens[2],
+			ts:        time.Unix(ts, 0),
+		}
+	}
+	wg.Done()
+}
+
+func parseFileGoroutines(reader *bufio.Reader) ([]customer, error) {
+	results := make(chan customer, 1024)
+	customers := make([]customer, 0)
+	wg := sync.WaitGroup{}
+
+loop:
+	for {
+		line, _, err := reader.ReadLine()
+		if err != nil {
+			switch err {
+			default:
+				return nil, err
+			case io.EOF:
+				break loop
+			}
+		}
+
+		// Add 1 to the wait group
+		wg.Add(1)
+		// Spin up a new goroutine
+		go parseLineGoroutines(&wg, string(line), results)
+	}
+
+	go func() {
+		// Wait for all the goroutines to complete before closing the channel
+		wg.Wait()
+		close(results)
+	}()
+
+	// Gather the results
+	for customer := range results {
+		customers = append(customers, customer)
+	}
+
+	return customers, nil
+}
+
+func parseLineGoroutines(wg *sync.WaitGroup, line string, output chan<- customer) {
+	tokens := strings.Split(line, ",")
+	ts, _ := strconv.ParseInt(tokens[3], 10, 64)
+	output <- customer{
+		id:        tokens[0],
+		firstName: tokens[1],
+		lastName:  tokens[2],
+		ts:        time.Unix(ts, 0),
+	}
+	wg.Done()
+}

concurrency/concurrency-not-magic_test.go

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+package concurrency
+
+import (
+	"bufio"
+	"bytes"
+	"io/ioutil"
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func Test_parseFile(t *testing.T) {
+	file, err := os.Open("input.csv")
+	require.NoError(t, err)
+	defer file.Close()
+	reader := bufio.NewReader(file)
+
+	customers, err := parseFile(reader)
+	require.NoError(t, err)
+	assert.Equal(t, 1_000_000, len(customers))
+}
+
+func Benchmark_parseFile(b *testing.B) {
+	benchmarkParseFile(b, parseFile)
+}
+
+func Benchmark_parseFileWorker(b *testing.B) {
+	benchmarkParseFile(b, parseFileWorker)
+}
+
+func Benchmark_parseFileGoroutines(b *testing.B) {
+	benchmarkParseFile(b, parseFileGoroutines)
+}
+
+func benchmarkParseFile(b *testing.B, f func(reader *bufio.Reader) ([]customer, error)) {
+	file, err := os.Open("input.csv")
+	require.NoError(b, err)
+	csv, _ := ioutil.ReadAll(file)
+	reader := bufio.NewReader(bytes.NewReader(csv))
+	b.ReportAllocs()
+	b.ResetTimer()
+
+	for i := 0; i < b.N; i++ {
+		f(reader)
+	}
+}

go.mod

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+module github.com/teivah/100-go-mistakes
+
+go 1.15
+
+require github.com/stretchr/testify v1.6.1

go.sum

@@ -0,0 +1,12 @@
+github.com/davecgh/go-spew v1.1.0 h1:ZDRjVQ15GmhC3fiQ8ni8+OwkZQO4DARzQgrnXU1Liz8=
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/objx v0.1.0 h1:4G4v2dO3VZwixGIRoQ5Lfboy6nUhCyYzaqnIAPPhYs4=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/testify v1.6.1 h1:hDPOHmpOpP40lSULcqw7IrRb/u7w6RpDC9399XyoNd0=
+github.com/stretchr/testify v1.6.1/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c h1:dUUwHk2QECo/6vqA44rthZ8ie2QXMNeKRTHCNY2nXvo=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=