fix: correct RLock scope in Context.Copy method

[1911860538]

No description provided.

[NezhaFan]

You are wrong, must add a read lock during the loop to prevent writing at this time. and maybe you don't understand the copy of map .

[1911860538]

You are wrong, must add a read lock during the loop to prevent writing at this time. and maybe you don't understand the copy of map .

c.mu.RLock() is used to protect c.Keys, not cp.Keys. cp.Keys does not require lock protection here because the Copy method is in the process of creating cp, so there is no read-write race condition for cp.Keys.Since the Copy method involves reading operations on c.Keys, my modification poses no issues.

[NezhaFan]

我觉得你在理解map拷贝或者读写锁 不太对。 m2 := m1 不需要加锁，只是拷贝了 map 的结构体。 对于 map 读写考虑并发的情况下，要加锁。

func main() {
	var mu sync.RWMutex
	n := 50000

	m1 := make(map[int]int, n)
	for i := 0; i < n; i++ {
		m1[i] = i
	}

	// 并发写入
	for i := 0; i < n; i++ {
		go func(i int) {
			mu.Lock()
			defer mu.Unlock()
			m1[i] = i
		}(i)
	}


        // 你的意思：直接赋值拷贝加锁
	mu.RLock()
	m2 := m1
	mu.RUnlock()

        // 应该这样：读的过程前后锁
        // mu.RLock()
	// 拷贝
	cp := make(map[int]int, n)
	for k, v := range m2 {
		cp[k] = v
	}
	// mu.RUnlock()
}