什麼是golang中的同步（sync.RWMutex）

我正在尋找大猩猩上下文來源代碼。我不明白它做了什麼同步，mutex.Lock，mutex.Unlock。當我從源代碼中移除mutex.Lock和Mutex.Unlock時，它仍在運行。什麼是golang中的同步（sync.RWMutex）

import (
    "net/http" 
    "sync" 
    "time" 
) 

var (
    mutex sync.RWMutex 
    data = make(map[*http.Request]map[interface{}]interface{}) 
    datat = make(map[*http.Request]int64) 
) 

// Set stores a value for a given key in a given request. 
func Set(r *http.Request, key, val interface{}) { 
    mutex.Lock() 
    if data[r] == nil { 
     data[r] = make(map[interface{}]interface{}) 
     datat[r] = time.Now().Unix() 
    } 
    data[r][key] = val 
    mutex.Unlock() 
}