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| package waitlist | |
| import "sync" | |
| type waitChanList []chan struct{} | |
| type WaitList struct { | |
| m map[string]waitChanList | |
| sync.RWMutex | |
| } | |
| // NewWaitList - an object to keep track of (labeled) wait queues | |
| func NewWaitList() *WaitList { | |
| return &WaitList{ | |
| m: make(map[string]waitChanList), | |
| } | |
| } | |
| // WaitIfBusy does one of two things: | |
| // 1. If there is no current wait create an empty wait list to signal that something is no running | |
| // 2. If there is a wait list create a chan and add it to the channel, pull to block from that channel | |
| func (wm *WaitList) WaitIfBusy(label string) { | |
| wm.Lock() | |
| wcs, ok := wm.m[label] | |
| if ok { | |
| // a request is in flight, ask this one to wait | |
| ch := make(chan struct{}) | |
| wm.m[label] = append(wcs, ch) | |
| wm.Unlock() | |
| <-ch | |
| } else { | |
| // this is currently the only update in flight, make a list for others | |
| wm.Lock() | |
| wm.m[label] = make(waitChanList, 0) | |
| wm.Unlock() | |
| } | |
| } | |
| // ReleaseAll unblocks all waiting channels. Return how many waiters were released | |
| func (wm *WaitList) ReleaseAll(label string) int { | |
| wm.Lock() | |
| defer wm.Unlock() | |
| w := wm.m[label] | |
| for _, ch := range w { | |
| ch <- struct{}{} | |
| } | |
| delete(wm.m, label) | |
| return len(w) | |
| } | |
| // ReleaseOne unblocks the first channel in the wait list and | |
| func (wm *WaitList) ReleaseOne(label string) int { | |
| wm.Lock() | |
| defer wm.Unlock() | |
| w := wm.m[label] | |
| if len(w) > 0 { | |
| w[0] <- struct{}{} | |
| wm.m[label] = w[1:] | |
| } else { | |
| delete(wm.m, label) | |
| } | |
| return len(w) - 1 | |
| } |
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