Add ratelimit task

go.mod

@@ -8,6 +8,7 @@ require (
 	github.com/armon/consul-api v0.0.0-20180202201655-eb2c6b5be1b6 // indirect
 	github.com/coreos/go-etcd v2.0.0+incompatible // indirect
 	github.com/cpuguy83/go-md2man v1.0.10 // indirect
+	github.com/davecgh/go-spew v1.1.1
 	github.com/go-redis/redis v6.15.7+incompatible
 	github.com/go-resty/resty/v2 v2.1.0
 	github.com/gofrs/uuid v3.2.0+incompatible

ratelimit/README.md

@@ -0,0 +1,16 @@
+# ratelimit
+
+Напишите примитив синхронизации, ограничивающий число вызовов на интервале времени.
+
+
+```go
+func NewLimiter(maxCount int, interval time.Duration) *Limiter
+
+func (l *Limiter) Acquire(ctx context.Context) error
+```
+
+`Limiter` должен гарантировать, что на любом интервале времени `interval`, не больше `maxCount` вызовов
+`Acquire` могут завершиться без ошибки.
+
+Каждый вызов `Acquire` должен либо завершаться успешно, либо завершаться с ошибкой в случае если `ctx` отменили
+во время ожидания.

ratelimit/rate.go

@@ -1,36 +0,0 @@
-package ratelimit
-
-import (
-	"fmt"
-	"strconv"
-	"strings"
-	"time"
-)
-
-// ParseRate parses rate in form of "N/D", e.g "10/1s" or "100/1ms"
-func ParseRate(rate string) (count int, interval time.Duration, err error) {
-	parts := strings.SplitN(rate, "/", 2)
-	if len(parts) != 2 {
-		err = fmt.Errorf("invalid rate format in %q: missing slash", rate)
-		return
-	}
-
-	count, err = strconv.Atoi(parts[0])
-	if err != nil {
-		err = fmt.Errorf("invalid rate format in %q: %v", rate, err)
-		return
-	}
-
-	interval, err = time.ParseDuration(parts[1])
-	if err != nil {
-		err = fmt.Errorf("invalid rate format in %q: %v", rate, err)
-		return
-	}
-
-	if interval < 0 {
-		err = fmt.Errorf("invalid rate format in %q: negative interval", rate)
-		return
-	}
-
-	return
-}

ratelimit/rate_test.go

@@ -1,32 +0,0 @@
-package ratelimit
-
-import (
-	"testing"
-	"time"
-
-	"github.com/stretchr/testify/require"
-)
-
-func TestParseRate(t *testing.T) {
-	count, dt, err := ParseRate("10/1s")
-	require.NoError(t, err)
-	require.Equal(t, 10, count)
-	require.Equal(t, time.Second, dt)
-
-	count, dt, err = ParseRate("1/1ms")
-	require.NoError(t, err)
-	require.Equal(t, 1, count)
-	require.Equal(t, time.Millisecond, dt)
-}
-
-func TestInvalidRate(t *testing.T) {
-	for _, invalid := range []string{
-		"",
-		"1/2",
-		"/10m",
-		"abc",
-	} {
-		_, _, err := ParseRate(invalid)
-		require.Errorf(t, err, "rate %q is invalid", invalid)
-	}
-}

ratelimit/ratelimit_test.go

@@ -2,6 +2,8 @@ package ratelimit
 
 import (
 	"context"
+	"math/rand"
+	"sort"
 	"sync"
 	"testing"
 	"time"
@@ -41,6 +43,56 @@ func TestSimpleLimitCancel(t *testing.T) {
 	require.Equal(t, context.DeadlineExceeded, err)
 }
 
+func TestTimeDistribution(t *testing.T) {
+	limit := NewLimiter(100, time.Second)
+
+	var lock sync.Mutex
+	okTimes := []time.Duration{}
+	start := time.Now()
+
+	var wg sync.WaitGroup
+	for i := 0; i < 500; i++ {
+		time.Sleep(time.Millisecond * 5)
+
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+
+			dt := time.Duration(rand.Float64() * float64(time.Second))
+			ctx, cancel := context.WithTimeout(context.Background(), dt)
+			defer cancel()
+
+			err := limit.Acquire(ctx)
+			if err != nil {
+				return
+			}
+
+			lock.Lock()
+			defer lock.Unlock()
+			okTimes = append(okTimes, time.Since(start))
+		}()
+	}
+
+	wg.Wait()
+
+	require.Greater(t, len(okTimes), 200, "At least 200 goroutines should succeed")
+
+	sort.Slice(okTimes, func(i, j int) bool {
+		return okTimes[i] < okTimes[j]
+	})
+
+	for i, dt := range okTimes {
+		j := sort.Search(len(okTimes)-i, func(j int) bool {
+			return okTimes[i+j] > dt+time.Second
+		})
+
+		require.Lessf(t, j, 130, "%d goroutines acquired semaphore on interval [%v, %v)", j, dt, dt+time.Second)
+	}
+
+	// Uncomment this line to see full distribution
+	// spew.Fdump(os.Stderr, okTimes)
+}
+
 func TestStressBlocking(t *testing.T) {
 	const (
 		N = 100