groupcache使用singleflight实现资源访问合并
/ Package singleflight provides a duplicate function call suppression // mechanism. package singleflight import "sync" // call is an in-flight or completed Do call type call struct { wg sync.WaitGroup val interface{} err error } // Group represents a class of work and forms a namespace in which // units of work can be executed with duplicate suppression. type Group struct { mu sync.Mutex // protects m m map[string]*call // lazily initialized } // Do executes and returns the results of the given function, making // sure that only one execution is in-flight for a given key at a // time. If a duplicate comes in, the duplicate caller waits for the // original to complete and receives the same results. func (g *Group) Do(key string, fn func() (interface{}, error)) (interface{}, error) { g.mu.Lock() if g.m == nil { g.m = make(map[string]*call) } if c, ok := g.m[key]; ok { g.mu.Unlock() c.wg.Wait() return c.val, c.err } c := new(call) c.wg.Add(1) g.m[key] = c g.mu.Unlock() c.val, c.err = fn() c.wg.Done() g.mu.Lock() delete(g.m, key) g.mu.Unlock() return c.val, c.err }