singleflight

g.m[key] ok ?

Y

结束

g.m == nil

开始

初始化g.m

c := new(call)c.wg.Add(1)g.m[key] = cg.mu.Unlock

g.mu.Lock

c.dups++g.mu.Unlockc.wg.Wait

N

type call struct {    wg sync.WaitGroup    dups int        val interface    err error    chans []chan<-Result    forgotten bool}type Result struct {    Val interface    Err error    Shared bool}type Group struct {    mu sync.Mutex    m map[string]*call}