From 9710b24e3e7d0045f88e886195ef21dd9c6023e2 Mon Sep 17 00:00:00 2001
From: Nedyalko Dyakov <nedyalko.dyakov@gmail.com>
Date: Sat, 29 Nov 2025 02:32:34 +0200
Subject: [PATCH] resolve semaphore leak

---
 internal/pool/pool.go               |   6 +-
 internal/pool/race_freeturn_test.go | 146 ++++++++++++++++++++++++++++
 2 files changed, 151 insertions(+), 1 deletion(-)
 create mode 100644 internal/pool/race_freeturn_test.go

diff --git a/internal/pool/pool.go b/internal/pool/pool.go
index 5ca6a29b..3da15ccd 100644
--- a/internal/pool/pool.go
+++ b/internal/pool/pool.go
@@ -576,7 +576,11 @@ func (p *ConnPool) queuedNewConn(ctx context.Context) (*Conn, error) {
 			// If dial completed before timeout, try to deliver connection to other waiters
 			if cn := w.cancel(); cn != nil {
 				p.putIdleConn(ctx, cn)
-				// freeTurn will be called by the dial goroutine or by the waiter who receives the connection
+				// Free the turn since:
+				// - Dial goroutine returned thinking delivery succeeded (tryDeliver returned true)
+				// - Original waiter won't call Put() (they got an error, not a connection)
+				// - Another waiter will receive this connection but won't free this turn
+				p.freeTurn()
 			}
 			// If dial hasn't completed yet, freeTurn will be called by the dial goroutine
 		}
diff --git a/internal/pool/race_freeturn_test.go b/internal/pool/race_freeturn_test.go
new file mode 100644
index 00000000..f998ddac
--- /dev/null
+++ b/internal/pool/race_freeturn_test.go
@@ -0,0 +1,146 @@
+package pool_test
+
+import (
+	"context"
+	"net"
+	"sync"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"github.com/redis/go-redis/v9/internal/pool"
+)
+
+// TestRaceConditionFreeTurn tests the race condition where:
+// 1. Dial completes and tryDeliver succeeds
+// 2. Waiter's context times out before receiving from result channel
+// 3. Waiter's defer retrieves connection via cancel() and delivers to another waiter
+// 4. Turn must be freed by the defer, not by dial goroutine or new waiter
+func TestRaceConditionFreeTurn(t *testing.T) {
+	// Create a pool with PoolSize=2 to make the race easier to trigger
+	opt := &pool.Options{
+		Dialer: func(ctx context.Context) (net.Conn, error) {
+			// Slow dial to allow context timeout to race with delivery
+			time.Sleep(50 * time.Millisecond)
+			return dummyDialer(ctx)
+		},
+		PoolSize:           2,
+		MaxConcurrentDials: 2,
+		DialTimeout:        1 * time.Second,
+		PoolTimeout:        1 * time.Second,
+	}
+
+	connPool := pool.NewConnPool(opt)
+	defer connPool.Close()
+
+	// Run multiple iterations to increase chance of hitting the race
+	for iteration := 0; iteration < 10; iteration++ {
+		// Request 1: Will timeout quickly
+		ctx1, cancel1 := context.WithTimeout(context.Background(), 30*time.Millisecond)
+		defer cancel1()
+
+		var wg sync.WaitGroup
+		wg.Add(2)
+
+		// Goroutine 1: Request with short timeout
+		go func() {
+			defer wg.Done()
+			cn, err := connPool.Get(ctx1)
+			if err == nil {
+				// If we got a connection, put it back
+				connPool.Put(ctx1, cn)
+			}
+			// Expected: context deadline exceeded
+		}()
+
+		// Goroutine 2: Request with longer timeout, should receive the orphaned connection
+		go func() {
+			defer wg.Done()
+			time.Sleep(20 * time.Millisecond) // Start slightly after first request
+			ctx2, cancel2 := context.WithTimeout(context.Background(), 200*time.Millisecond)
+			defer cancel2()
+
+			cn, err := connPool.Get(ctx2)
+			if err != nil {
+				t.Logf("Request 2 error: %v", err)
+				return
+			}
+			// Got connection, put it back
+			connPool.Put(ctx2, cn)
+		}()
+
+		wg.Wait()
+
+		// Give some time for all operations to complete
+		time.Sleep(100 * time.Millisecond)
+
+		// Check QueueLen - should be 0 (all turns freed)
+		queueLen := connPool.QueueLen()
+		if queueLen != 0 {
+			t.Errorf("Iteration %d: QueueLen = %d, expected 0 (turn leak detected!)", iteration, queueLen)
+		}
+	}
+}
+
+// TestRaceConditionFreeTurnStress is a stress test for the race condition
+func TestRaceConditionFreeTurnStress(t *testing.T) {
+	var dialIndex atomic.Int32
+	opt := &pool.Options{
+		Dialer: func(ctx context.Context) (net.Conn, error) {
+			// Variable dial time to create more race opportunities
+			// Use atomic increment to avoid data race
+			idx := dialIndex.Add(1)
+			time.Sleep(time.Duration(10+idx%40) * time.Millisecond)
+			return dummyDialer(ctx)
+		},
+		PoolSize:           10,
+		MaxConcurrentDials: 10,
+		DialTimeout:        1 * time.Second,
+		PoolTimeout:        500 * time.Millisecond,
+	}
+
+	connPool := pool.NewConnPool(opt)
+	defer connPool.Close()
+
+	const numRequests = 50
+
+	var wg sync.WaitGroup
+	wg.Add(numRequests)
+
+	// Launch many concurrent requests with varying timeouts
+	for i := 0; i < numRequests; i++ {
+		go func(i int) {
+			defer wg.Done()
+
+			// Varying timeouts to create race conditions
+			timeout := time.Duration(20+i%80) * time.Millisecond
+			ctx, cancel := context.WithTimeout(context.Background(), timeout)
+			defer cancel()
+
+			cn, err := connPool.Get(ctx)
+			if err == nil {
+				// Simulate some work
+				time.Sleep(time.Duration(i%20) * time.Millisecond)
+				connPool.Put(ctx, cn)
+			}
+		}(i)
+	}
+
+	wg.Wait()
+
+	// Give time for all cleanup to complete
+	time.Sleep(200 * time.Millisecond)
+
+	// Check for turn leaks
+	queueLen := connPool.QueueLen()
+	if queueLen != 0 {
+		t.Errorf("QueueLen = %d, expected 0 (turn leak detected!)", queueLen)
+		t.Errorf("This indicates that some turns were never freed")
+	}
+
+	// Also check pool stats
+	stats := connPool.Stats()
+	t.Logf("Pool stats: Hits=%d, Misses=%d, Timeouts=%d, TotalConns=%d, IdleConns=%d",
+		stats.Hits, stats.Misses, stats.Timeouts, stats.TotalConns, stats.IdleConns)
+}
+