package missinggo
import "sync"
type ongoing struct {
do sync.Mutex
users int
}
type SingleFlight struct {
mu sync.Mutex
ongoing map[string]*ongoing
}
type Operation struct {
sf *SingleFlight
id string
}
func (op Operation) Unlock() {
op.sf.Unlock(op.id)
}
func (me *SingleFlight) Lock(id string) Operation {
me.mu.Lock()
on, ok := me.ongoing[id]
if !ok {
on = new(ongoing)
if me.ongoing == nil {
me.ongoing = make(map[string]*ongoing)
}
me.ongoing[id] = on
}
on.users++
me.mu.Unlock()
on.do.Lock()
return Operation{me, id}
}
func (me *SingleFlight) Unlock(id string) {
me.mu.Lock()
on := me.ongoing[id]
on.do.Unlock()
on.users--
if on.users == 0 {
delete(me.ongoing, id)
}
me.mu.Unlock()
}