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package mru
// Touch moves key to the front, best-effort.
//
// When key is already the most-recently-used,
// Touch is lock-free and allocation-free;
// this is the common case.
// Otherwise Touch reorders under a non-blocking lock attempt,
// so a read never blocks merely to reorder.
// A contended attempt,
// or a key that is not a member,
// leaves the order unchanged.
func (order *Order[K]) Touch(key K) {
keys := order.Keys()
if len(keys) == 0 || keys[0] == key {
return
}
if !order.mu.TryLock() {
return
}
defer order.mu.Unlock()
// The snapshot may have changed before we took the lock.
keys = order.Keys()
index := -1
for i, candidate := range keys {
if candidate == key {
index = i
break
}
}
if index <= 0 {
return
}
next := make([]K, 0, len(keys))
next = append(next, key)
next = append(next, keys[:index]...)
next = append(next, keys[index+1:]...)
order.snapshot.Store(&next)
}
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