You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: cache.go
    path of file: ./repos/protoreflect/desc
    
    the code of the file until where you have to start completion: package desc

import (
	"sync"

	"google.golang.org/protobuf/reflect/protorefl
    
func (c *lockingCache) withLock(fn func(descriptorCache)) {
	c.cacheMu.Lock()
	defer c.cacheMu.Unlock()
	// Pass the underlying mapCache. We don't want fn to use
	// c.get or c.put sine we already have the lock. So those
	// methods would try to re-acquire and then deadlock!
	fn(c.cache)
}