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package ctxlock
import (
"context"
"time"
)
// Lock will attempt to acquire a lock for the given ID.
//
// If Lock returns nil, Unlock must be called to release the lock,
// even if the context is canceled.
func (l *IDLocker[K]) Lock(ctx context.Context, id K) error {
l.mx.Lock()
if l.count[id] < l.cfg.MaxHeld {
// fast path, no queue
l.count[id]++
l.mx.Unlock()
return nil
}
if l.cfg.MaxWait != -1 && len(l.queue[id]) >= l.cfg.MaxWait {
l.mx.Unlock()
return ErrQueueFull
}
if l.cfg.Timeout > 0 {
var cancel func(error)
ctx, cancel = context.WithCancelCause(ctx)
t := time.AfterFunc(l.cfg.Timeout, func() { cancel(ErrTimeout) })
defer t.Stop()
defer cancel(nil)
}
// slow path, queue to hold our spot
ch := make(chan struct{})
l.queue[id] = append(l.queue[id], ch)
l.mx.Unlock()
select {
case <-ctx.Done():
close(ch) // Ensure Unlock knows we are abandoning our spot.
l.mx.Lock()
defer l.mx.Unlock()
for i, c := range l.queue[id] {
if c != ch {
continue
}
l.queue[id] = append(l.queue[id][:i], l.queue[id][i+1:]...)
break
}
if len(l.queue[id]) == 0 {
delete(l.queue, id) // cleanup so the map doesn't grow forever
}
return context.Cause(ctx)
case ch <- struct{}{}:
// we have the lock, queue and count have been updated by Unlock
}
return nil
}
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