From 50eb82660bb642408c5f894de1703b9decbecca0 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Petr=20Stuchl=C3=ADk?= <stuchl4n3k@gmail.com>
Date: Tue, 17 Mar 2026 19:15:19 +0100
Subject: [PATCH] fix: data race in ehash due to unsynchronized lazy init of
 Map.typ

---
 go.mod |  2 +-
 map.go | 28 ++++++++++++++--------------
 2 files changed, 15 insertions(+), 15 deletions(-)

diff --git a/go.mod b/go.mod
index 5714ccc..2e9e8af 100644
--- a/go.mod
+++ b/go.mod
@@ -1,3 +1,3 @@
 module github.com/lrita/cmap
 
-go 1.18
+go 1.19
diff --git a/map.go b/map.go
index 46334bb..2bbd9f5 100644
--- a/map.go
+++ b/map.go
@@ -16,7 +16,7 @@ import (
 type Map[K comparable, V any] struct {
 	lock  sync.Mutex
 	inode unsafe.Pointer // *inode2
-	typ   *rtype
+	typ   atomic.Pointer[rtype]
 	count int64
 }
 
@@ -400,23 +400,23 @@ func efaceOf(ep *any) *eface {
 }
 
 func (m *Map[K, V]) ehash(i K) uintptr {
-	if m.typ == nil {
-		func() {
-			m.lock.Lock()
-			defer m.lock.Unlock()
-			if m.typ == nil {
-				// if K is interface type, then the direct reflect.TypeOf(K).Kind return reflect.Ptr
-				if typ := reflect.TypeOf(&i); typ.Elem().Kind() == reflect.Interface {
-					panic("not support interface type")
-				}
-				var e any = i
-				m.typ = efaceOf(&e).typ
+	typ := m.typ.Load()
+	if typ == nil {
+		m.lock.Lock()
+		if m.typ.Load() == nil {
+			// if K is interface type, then the direct reflect.TypeOf(K).Kind return reflect.Ptr
+			if typ := reflect.TypeOf(&i); typ.Elem().Kind() == reflect.Interface {
+				panic("not support interface type")
 			}
-		}()
+			var e any = i
+			m.typ.Store(efaceOf(&e).typ)
+		}
+		m.lock.Unlock()
+		typ = m.typ.Load()
 	}
 
 	var f eface
-	f.typ = m.typ
+	f.typ = typ
 	if f.typ.IsDirectIface() {
 		f.data = *(*unsafe.Pointer)(unsafe.Pointer(&i))
 	} else {