[#4] limiting: Add limiter

Signed-off-by: Aleksey Savchuk <a.savchuk@yadro.com>

limiting/limiter.go

@@ -0,0 +1,75 @@
+package limiting
+
+import (
+	"fmt"
+
+	"git.frostfs.info/TrueCloudLab/frostfs-qos/limiting/semaphore"
+)
+
+type ReleaseFunc func()
+
+type Limiter interface {
+	// Acquire attempts to reserve a slot without blocking.
+	//
+	// Returns a release function and true if successful. The function must be
+	// called to release the limiter. The function must be called exactly once.
+	// Calling the function more that once will cause incorrect behavior of the
+	// limiter.
+	//
+	// Returns nil and false if fails.
+	//
+	// If the key was not defined in the limiter, no limit is applied.
+	Acquire(key string) (ReleaseFunc, bool)
+}
+
+type SemaphoreLimiter struct {
+	m map[string]*semaphore.Semaphore
+}
+
+// KeyLimit defines a concurrency limit for a set of keys.
+//
+// All keys of one set share the same limit.
+// Keys of different sets have separate limits.
+//
+// Sets must not overlap.
+type KeyLimit struct {
+	Keys  []string
+	Limit int64
+}
+
+func NewSemaphoreLimiter(limits []KeyLimit) (*SemaphoreLimiter, error) {
+	lr := SemaphoreLimiter{make(map[string]*semaphore.Semaphore)}
+	for _, limit := range limits {
+		if limit.Limit < 0 {
+			return nil, fmt.Errorf("invalid limit %d", limit.Limit)
+		}
+		sem := semaphore.NewSemaphore(limit.Limit)
+
+		if err := lr.addLimit(&limit, sem); err != nil {
+			return nil, err
+		}
+	}
+	return &lr, nil
+}
+
+func (lr *SemaphoreLimiter) addLimit(limit *KeyLimit, sem *semaphore.Semaphore) error {
+	for _, key := range limit.Keys {
+		if _, exists := lr.m[key]; exists {
+			return fmt.Errorf("duplicate key %q", key)
+		}
+		lr.m[key] = sem
+	}
+	return nil
+}
+
+func (lr *SemaphoreLimiter) Acquire(key string) (ReleaseFunc, bool) {
+	sem, ok := lr.m[key]
+	if !ok {
+		return func() {}, true
+	}
+
+	if ok := sem.Acquire(); ok {
+		return func() { sem.Release() }, true
+	}
+	return nil, false
+}

limiting/limiter_test.go

@@ -0,0 +1,138 @@
+package limiting_test
+
+import (
+	"sync"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"git.frostfs.info/TrueCloudLab/frostfs-qos/limiting"
+	"github.com/stretchr/testify/require"
+)
+
+const (
+	operationDuration = 10 * time.Millisecond
+	operationCount    = 64
+)
+
+type testCase struct {
+	keys         []string
+	limit        int64
+	withoutLimit bool
+	failCount    atomic.Int64
+}
+
+func TestLimiter(t *testing.T) {
+	testLimiter(t, func(kl []limiting.KeyLimit) (limiting.Limiter, error) {
+		return limiting.NewSemaphoreLimiter(kl)
+	})
+}
+
+func testLimiter(t *testing.T, getLimiter func([]limiting.KeyLimit) (limiting.Limiter, error)) {
+	t.Run("duplicate key", func(t *testing.T) {
+		_, err := getLimiter([]limiting.KeyLimit{
+			{[]string{"A", "B"}, 10},
+			{[]string{"B", "C"}, 10},
+		})
+		require.Error(t, err)
+	})
+
+	testCases := []*testCase{
+		{keys: []string{"A"}, limit: operationCount / 4},
+		{keys: []string{"B"}, limit: operationCount / 2},
+		{keys: []string{"C", "D"}, limit: operationCount / 4},
+		{keys: []string{"E"}, limit: 2 * operationCount},
+		{keys: []string{"F"}, withoutLimit: true},
+	}
+
+	lr, err := getLimiter(getLimits(testCases))
+	require.NoError(t, err)
+
+	tasks := createTestTasks(testCases, lr)
+
+	t.Run("first run", func(t *testing.T) {
+		executeTasks(tasks...)
+		verifyResults(t, testCases)
+	})
+
+	resetFailCounts(testCases)
+
+	t.Run("repeated run", func(t *testing.T) {
+		executeTasks(tasks...)
+		verifyResults(t, testCases)
+	})
+}
+
+func getLimits(testCases []*testCase) []limiting.KeyLimit {
+	var limits []limiting.KeyLimit
+	for _, tc := range testCases {
+		if tc.withoutLimit {
+			continue
+		}
+		limits = append(limits, limiting.KeyLimit{
+			Keys:  tc.keys,
+			Limit: int64(tc.limit),
+		})
+	}
+	return limits
+}
+
+func createTestTasks(testCases []*testCase, lr limiting.Limiter) []func() {
+	var tasks []func()
+	for _, tc := range testCases {
+		for _, key := range tc.keys {
+			tasks = append(tasks, func() {
+				executeTaskN(operationCount, func() { acquireAndExecute(tc, lr, key) })
+			})
+		}
+	}
+	return tasks
+}
+
+func acquireAndExecute(tc *testCase, lr limiting.Limiter, key string) {
+	release, ok := lr.Acquire(key)
+	if !ok {
+		tc.failCount.Add(1)
+		return
+	}
+	defer release()
+	time.Sleep(operationDuration)
+}
+
+func executeTasks(tasks ...func()) {
+	var g sync.WaitGroup
+
+	g.Add(len(tasks))
+	for _, task := range tasks {
+		go func() {
+			defer g.Done()
+			task()
+		}()
+	}
+	g.Wait()
+}
+
+func executeTaskN(N int, task func()) {
+	tasks := make([]func(), N)
+	for i := range N {
+		tasks[i] = task
+	}
+	executeTasks(tasks...)
+}
+
+func verifyResults(t *testing.T, testCases []*testCase) {
+	for _, tc := range testCases {
+		var expectedFailCount int64
+		if !tc.withoutLimit {
+			numKeys := int64(len(tc.keys))
+			expectedFailCount = max(operationCount*numKeys-tc.limit, 0)
+		}
+		require.Equal(t, expectedFailCount, tc.failCount.Load())
+	}
+}
+
+func resetFailCounts(testCases []*testCase) {
+	for _, tc := range testCases {
+		tc.failCount.Store(0)
+	}
+}

limiting/semaphore/semaphore.go

@@ -0,0 +1,27 @@
+package semaphore
+
+import (
+	"sync/atomic"
+)
+
+type Semaphore struct {
+	count atomic.Int64
+	limit int64
+}
+
+func NewSemaphore(size int64) *Semaphore {
+	return &Semaphore{limit: size}
+}
+
+func (s *Semaphore) Acquire() bool {
+	v := s.count.Add(1)
+	if v > s.limit {
+		s.count.Add(-1)
+		return false
+	}
+	return true
+}
+
+func (s *Semaphore) Release() {
+	s.count.Add(-1)
+}