R74: recv handler panics, cache TTL race fix

internal/cache/backends/race_regression_test.go

@@ -0,0 +1,50 @@
+package backends
+
+import (
+	"context"
+	"sync"
+	"testing"
+	"time"
+)
+
+// TestCache_TTLReadUnderConcurrentExpire exercises get/exists/ttl fast
+// paths racing with an in-place Expire that mutates expiresAt. Before
+// the fix the fast paths read expiresAt outside the lock, so under -race
+// this reports a data race on memoryCacheItem.expiresAt.
+func TestCache_TTLReadUnderConcurrentExpire(t *testing.T) {
+	c := NewMemoryCacheBackend(10000, 1024*1024*64, 0)
+	defer c.Close()
+
+	ctx := context.Background()
+	if err := c.Set(ctx, "k", "v", time.Hour); err != nil {
+		t.Fatalf("set: %v", err)
+	}
+
+	stop := make(chan struct{})
+	var wg sync.WaitGroup
+	for i := 0; i < 4; i++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			for {
+				select {
+				case <-stop:
+					return
+				default:
+				}
+				_, _ = c.Get(ctx, "k")
+				_, _ = c.Exists(ctx, "k")
+				_, _ = c.TTL(ctx, "k")
+			}
+		}()
+	}
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		for i := 0; i < 2000; i++ {
+			_ = c.Expire(ctx, "k", time.Hour)
+		}
+		close(stop)
+	}()
+	wg.Wait()
+}