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linkedhashmap.go
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linkedhashmap.go
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// Copyright (C) 2019-2022, Ava Labs, Inte. All rights reserved.
// See the file LICENSE for licensing terms.
package linkedhashmap
import (
"container/list"
"sync"
"github.com/ava-labs/avalanchego/ids"
)
// Hashmap provides an O(1) mapping from a comparable key to any value.
// Comparable is defined by https://golang.org/ref/spec#Comparison_operators.
type Hashmap interface {
Put(key, val interface{})
Get(key interface{}) (val interface{}, exists bool)
Delete(key interface{})
Len() int
}
// LinkedHashmap is a hashmap that keeps track of the oldest pairing an the
// newest pairing.
type LinkedHashmap interface {
Hashmap
Oldest() (key interface{}, val interface{}, exists bool)
Newest() (key interface{}, val interface{}, exists bool)
NewIterator() Iter
}
// Iterates over the keys and values in a LinkedHashmap
// from oldest to newest elements.
// Assumes the underlying LinkedHashmap is not modified while
// the iterator is in use, except to delete elements that
// have already been iterated over.
type Iter interface {
Next() bool
Key() interface{}
Value() interface{}
}
type keyValue struct {
key interface{}
value interface{}
}
type linkedHashmap struct {
lock sync.RWMutex
entryMap map[interface{}]*list.Element
entryList *list.List
}
func New() LinkedHashmap {
return &linkedHashmap{
entryMap: make(map[interface{}]*list.Element),
entryList: list.New(),
}
}
func (lh *linkedHashmap) Put(key, val interface{}) {
lh.lock.Lock()
defer lh.lock.Unlock()
lh.put(key, val)
}
func (lh *linkedHashmap) Get(key interface{}) (interface{}, bool) {
lh.lock.Lock()
defer lh.lock.Unlock()
return lh.get(key)
}
func (lh *linkedHashmap) Delete(key interface{}) {
lh.lock.Lock()
defer lh.lock.Unlock()
lh.delete(key)
}
func (lh *linkedHashmap) Len() int {
lh.lock.Lock()
defer lh.lock.Unlock()
return lh.len()
}
func (lh *linkedHashmap) Oldest() (interface{}, interface{}, bool) {
lh.lock.Lock()
defer lh.lock.Unlock()
return lh.oldest()
}
func (lh *linkedHashmap) Newest() (interface{}, interface{}, bool) {
lh.lock.Lock()
defer lh.lock.Unlock()
return lh.newest()
}
func (lh *linkedHashmap) put(key, value interface{}) {
if e, ok := lh.entryMap[key]; ok {
lh.entryList.MoveToBack(e)
e.Value = keyValue{
key: key,
value: value,
}
} else {
lh.entryMap[key] = lh.entryList.PushBack(keyValue{
key: key,
value: value,
})
}
}
func (lh *linkedHashmap) get(key interface{}) (interface{}, bool) {
if e, ok := lh.entryMap[key]; ok {
return e.Value.(keyValue).value, true
}
return nil, false
}
func (lh *linkedHashmap) delete(key interface{}) {
if e, ok := lh.entryMap[key]; ok {
lh.entryList.Remove(e)
delete(lh.entryMap, key)
}
}
func (lh *linkedHashmap) len() int { return len(lh.entryMap) }
func (lh *linkedHashmap) oldest() (interface{}, interface{}, bool) {
if val := lh.entryList.Front(); val != nil {
return val.Value.(keyValue).key, val.Value.(keyValue).value, true
}
return nil, nil, false
}
func (lh *linkedHashmap) newest() (interface{}, interface{}, bool) {
if val := lh.entryList.Back(); val != nil {
return val.Value.(keyValue).key, val.Value.(keyValue).value, true
}
return nil, nil, false
}
func (lh *linkedHashmap) NewIterator() Iter {
return &iterator{lh: lh}
}
type iterator struct {
lh *linkedHashmap
key interface{}
value interface{}
next *list.Element
initialized, exhausted bool
}
func (it *iterator) Next() bool {
// If the iterator has been exhausted, there is no next value.
if it.exhausted {
it.key = ids.Empty
it.value = nil
it.next = nil
return false
}
it.lh.lock.RLock()
defer it.lh.lock.RUnlock()
// If the iterator was not yet initialized, do it now.
if !it.initialized {
it.initialized = true
oldest := it.lh.entryList.Front()
if oldest == nil {
it.exhausted = true
it.key = ids.Empty
it.value = nil
it.next = nil
return false
}
it.next = oldest
}
// It's important to ensure that [it.next] is not nil
// by not deleting elements that have not yet been iterated
// over from [it.lh]
it.key = it.next.Value.(keyValue).key
it.value = it.next.Value.(keyValue).value
it.next = it.next.Next() // Next time, return next element
it.exhausted = it.next == nil
return true
}
func (it *iterator) Key() interface{} { return it.key }
func (it *iterator) Value() interface{} { return it.value }