pkg/ratelimit: introduce an executor that can run with a limiter

pkg/ratelimit/concurrency_limiter.go

@@ -14,24 +14,33 @@
 
 package ratelimit
 
-import "github.com/tikv/pd/pkg/utils/syncutil"
+import (
+	"context"
 
-type concurrencyLimiter struct {
-	mu      syncutil.RWMutex
+	"github.com/tikv/pd/pkg/utils/syncutil"
+)
+
+// ConcurrencyLimiter is a limiter that limits the number of concurrent tasks.
+type ConcurrencyLimiter struct {
+	mu      syncutil.Mutex
 	current uint64
+	waiting uint64
 	limit   uint64
 
 	// statistic
 	maxLimit uint64
+	queue    chan *TaskToken
 }
 
-func newConcurrencyLimiter(limit uint64) *concurrencyLimiter {
-	return &concurrencyLimiter{limit: limit}
+// NewConcurrencyLimiter creates a new ConcurrencyLimiter.
+func NewConcurrencyLimiter(limit uint64) *ConcurrencyLimiter {
+	return &ConcurrencyLimiter{limit: limit, queue: make(chan *TaskToken, limit)}
 }
 
 const unlimit = uint64(0)
 
-func (l *concurrencyLimiter) allow() bool {
+// old interface. only used in the ratelimiter package.
+func (l *ConcurrencyLimiter) allow() bool {
 	l.mu.Lock()
 	defer l.mu.Unlock()
 
@@ -45,7 +54,8 @@ func (l *concurrencyLimiter) allow() bool {
 	return false
 }
 
-func (l *concurrencyLimiter) release() {
+// old interface. only used in the ratelimiter package.
+func (l *ConcurrencyLimiter) release() {
 	l.mu.Lock()
 	defer l.mu.Unlock()
 
@@ -54,28 +64,32 @@ func (l *concurrencyLimiter) release() {
 	}
 }
 
-func (l *concurrencyLimiter) getLimit() uint64 {
-	l.mu.RLock()
-	defer l.mu.RUnlock()
+// old interface. only used in the ratelimiter package.
+func (l *ConcurrencyLimiter) getLimit() uint64 {
+	l.mu.Lock()
+	defer l.mu.Unlock()
 
 	return l.limit
 }
 
-func (l *concurrencyLimiter) setLimit(limit uint64) {
+// old interface. only used in the ratelimiter package.
+func (l *ConcurrencyLimiter) setLimit(limit uint64) {
 	l.mu.Lock()
 	defer l.mu.Unlock()
 
 	l.limit = limit
 }
 
-func (l *concurrencyLimiter) getCurrent() uint64 {
-	l.mu.RLock()
-	defer l.mu.RUnlock()
+// GetRunningTasksNum returns the number of running tasks.
+func (l *ConcurrencyLimiter) GetRunningTasksNum() uint64 {
+	l.mu.Lock()
+	defer l.mu.Unlock()
 
 	return l.current
 }
 
-func (l *concurrencyLimiter) getMaxConcurrency() uint64 {
+// old interface. only used in the ratelimiter package.
+func (l *ConcurrencyLimiter) getMaxConcurrency() uint64 {
 	l.mu.Lock()
 	defer func() {
 		l.maxLimit = l.current
@@ -84,3 +98,58 @@ func (l *concurrencyLimiter) getMaxConcurrency() uint64 {
 
 	return l.maxLimit
 }
+
+// GetWaitingTasksNum returns the number of waiting tasks.
+func (l *ConcurrencyLimiter) GetWaitingTasksNum() uint64 {
+	l.mu.Lock()
+	defer l.mu.Unlock()
+	return l.waiting
+}
+
+// Acquire acquires a token from the limiter. which will block until a token is available or ctx is done, like Timeout.
+func (l *ConcurrencyLimiter) Acquire(ctx context.Context) (*TaskToken, error) {
+	l.mu.Lock()
+	if l.current >= l.limit {
+		l.waiting++
+		l.mu.Unlock()
+		// block the waiting task on the caller goroutine
+		select {
+		case <-ctx.Done():
+			l.mu.Lock()
+			l.waiting--
+			l.mu.Unlock()
+			return nil, ctx.Err()
+		case token := <-l.queue:
+			l.mu.Lock()
+			token.released = false
+			l.current++
+			l.waiting--
+			l.mu.Unlock()
+			return token, nil
+		}
+	}
+	l.current++
+	token := &TaskToken{limiter: l}
+	l.mu.Unlock()
+	return token, nil
+}
+
+// TaskToken is a token that must be released after the task is done.
+type TaskToken struct {
+	released bool
+	limiter  *ConcurrencyLimiter
+}
+
+// Release releases the token.
+func (tt *TaskToken) Release() {
+	tt.limiter.mu.Lock()
+	defer tt.limiter.mu.Unlock()
+	if tt.released {
+		return
+	}
+	tt.released = true
+	tt.limiter.current--
+	if len(tt.limiter.queue) < int(tt.limiter.limit) {
+		tt.limiter.queue <- tt
+	}
+}

pkg/ratelimit/concurrency_limiter_test.go

@@ -15,15 +15,20 @@
 package ratelimit
 
 import (
+	"context"
+	"fmt"
+	"sync"
+	"sync/atomic"
 	"testing"
+	"time"
 
 	"github.com/stretchr/testify/require"
 )
 
 func TestConcurrencyLimiter(t *testing.T) {
 	t.Parallel()
 	re := require.New(t)
-	cl := newConcurrencyLimiter(10)
+	cl := NewConcurrencyLimiter(10)
 	for i := 0; i < 10; i++ {
 		re.True(cl.allow())
 	}
@@ -35,20 +40,89 @@ func TestConcurrencyLimiter(t *testing.T) {
 	re.Equal(uint64(10), cl.getMaxConcurrency())
 	cl.setLimit(5)
 	re.Equal(uint64(5), cl.getLimit())
-	re.Equal(uint64(10), cl.getCurrent())
+	re.Equal(uint64(10), cl.GetRunningTasksNum())
 	cl.release()
-	re.Equal(uint64(9), cl.getCurrent())
+	re.Equal(uint64(9), cl.GetRunningTasksNum())
 	for i := 0; i < 9; i++ {
 		cl.release()
 	}
 	re.Equal(uint64(10), cl.getMaxConcurrency())
 	for i := 0; i < 5; i++ {
 		re.True(cl.allow())
 	}
-	re.Equal(uint64(5), cl.getCurrent())
+	re.Equal(uint64(5), cl.GetRunningTasksNum())
 	for i := 0; i < 5; i++ {
 		cl.release()
 	}
 	re.Equal(uint64(5), cl.getMaxConcurrency())
 	re.Equal(uint64(0), cl.getMaxConcurrency())
 }
+
+func TestConcurrencyLimiter2(t *testing.T) {
+	limit := uint64(2)
+	limiter := NewConcurrencyLimiter(limit)
+
+	require.Equal(t, uint64(0), limiter.GetRunningTasksNum(), "Expected running tasks to be 0")
+	require.Equal(t, uint64(0), limiter.GetWaitingTasksNum(), "Expected waiting tasks to be 0")
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	// Acquire two tokens
+	token1, err := limiter.Acquire(ctx)
+	require.NoError(t, err, "Failed to acquire token")
+
+	token2, err := limiter.Acquire(ctx)
+	require.NoError(t, err, "Failed to acquire token")
+
+	require.Equal(t, limit, limiter.GetRunningTasksNum(), "Expected running tasks to be 2")
+
+	// Try to acquire third token, it should not be able to acquire immediately due to limit
+	go func() {
+		_, err := limiter.Acquire(ctx)
+		require.NoError(t, err, "Failed to acquire token")
+	}()
+
+	time.Sleep(100 * time.Millisecond) // Give some time for the goroutine to run
+	require.Equal(t, uint64(1), limiter.GetWaitingTasksNum(), "Expected waiting tasks to be 1")
+
+	// Release a token
+	token1.Release()
+	time.Sleep(100 * time.Millisecond) // Give some time for the goroutine to run
+	require.Equal(t, uint64(2), limiter.GetRunningTasksNum(), "Expected running tasks to be 2")
+	require.Equal(t, uint64(0), limiter.GetWaitingTasksNum(), "Expected waiting tasks to be 0")
+
+	// Release the second token
+	token2.Release()
+	time.Sleep(100 * time.Millisecond) // Give some time for the goroutine to run
+	require.Equal(t, uint64(1), limiter.GetRunningTasksNum(), "Expected running tasks to be 1")
+}
+
+func TestConcurrencyLimiterAcquire(t *testing.T) {
+	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
+	defer cancel()
+
+	limiter := NewConcurrencyLimiter(20)
+	sum := int64(0)
+	start := time.Now()
+	wg := &sync.WaitGroup{}
+	wg.Add(100)
+	for i := 0; i < 100; i++ {
+		go func(i int) {
+			defer wg.Done()
+			token, err := limiter.Acquire(ctx)
+			if err != nil {
+				fmt.Printf("Task %d failed to acquire: %v\n", i, err)
+				return
+			}
+			defer token.Release()
+			// simulate takes some time
+			time.Sleep(10 * time.Millisecond)
+			atomic.AddInt64(&sum, 1)
+		}(i)
+	}
+	wg.Wait()
+	// We should have 20 tasks running concurrently, so it should take at least 50ms to complete
+	require.Greater(t, time.Since(start).Milliseconds(), int64(50))
+	require.Equal(t, int64(100), sum)
+}

pkg/ratelimit/limiter.go

@@ -36,18 +36,18 @@ type DimensionConfig struct {
 
 type limiter struct {
 	mu          syncutil.RWMutex
-	concurrency *concurrencyLimiter
+	concurrency *ConcurrencyLimiter
 	rate        *RateLimiter
 }
 
 func newLimiter() *limiter {
 	lim := &limiter{
-		concurrency: newConcurrencyLimiter(0),
+		concurrency: NewConcurrencyLimiter(0),
 	}
 	return lim
 }
 
-func (l *limiter) getConcurrencyLimiter() *concurrencyLimiter {
+func (l *limiter) getConcurrencyLimiter() *ConcurrencyLimiter {
 	l.mu.RLock()
 	defer l.mu.RUnlock()
 	return l.concurrency
@@ -81,7 +81,7 @@ func (l *limiter) getQPSLimiterStatus() (limit rate.Limit, burst int) {
 func (l *limiter) getConcurrencyLimiterStatus() (limit uint64, current uint64) {
 	baseLimiter := l.getConcurrencyLimiter()
 	if baseLimiter != nil {
-		return baseLimiter.getLimit(), baseLimiter.getCurrent()
+		return baseLimiter.getLimit(), baseLimiter.GetRunningTasksNum()
 	}
 	return 0, 0
 }
@@ -101,7 +101,7 @@ func (l *limiter) updateConcurrencyConfig(limit uint64) UpdateStatus {
 		}
 		l.concurrency.setLimit(limit)
 	} else {
-		l.concurrency = newConcurrencyLimiter(limit)
+		l.concurrency = NewConcurrencyLimiter(limit)
 	}
 	return ConcurrencyChanged
 }