gotosocial/vendor/github.com/cornelk/hashmap/hashmap.go

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// Package hashmap provides a lock-free and thread-safe HashMap.
package hashmap
import (
"bytes"
"fmt"
"reflect"
"strconv"
"sync/atomic"
"unsafe"
)
// Map implements a read optimized hash map.
type Map[Key hashable, Value any] struct {
hasher func(Key) uintptr
store atomic.Pointer[store[Key, Value]] // pointer to a map instance that gets replaced if the map resizes
linkedList *List[Key, Value] // key sorted linked list of elements
// resizing marks a resizing operation in progress.
// this is using uintptr instead of atomic.Bool to avoid using 32 bit int on 64 bit systems
resizing atomic.Uintptr
}
// New returns a new map instance.
func New[Key hashable, Value any]() *Map[Key, Value] {
return NewSized[Key, Value](defaultSize)
}
// NewSized returns a new map instance with a specific initialization size.
func NewSized[Key hashable, Value any](size uintptr) *Map[Key, Value] {
m := &Map[Key, Value]{}
m.allocate(size)
m.setDefaultHasher()
return m
}
// SetHasher sets a custom hasher.
func (m *Map[Key, Value]) SetHasher(hasher func(Key) uintptr) {
m.hasher = hasher
}
// Len returns the number of elements within the map.
func (m *Map[Key, Value]) Len() int {
return m.linkedList.Len()
}
// Get retrieves an element from the map under given hash key.
func (m *Map[Key, Value]) Get(key Key) (Value, bool) {
hash := m.hasher(key)
for element := m.store.Load().item(hash); element != nil; element = element.Next() {
if element.keyHash == hash && element.key == key {
return element.Value(), true
}
if element.keyHash > hash {
return *new(Value), false
}
}
return *new(Value), false
}
// GetOrInsert returns the existing value for the key if present.
// Otherwise, it stores and returns the given value.
// The returned bool is true if the value was loaded, false if stored.
func (m *Map[Key, Value]) GetOrInsert(key Key, value Value) (Value, bool) {
hash := m.hasher(key)
var newElement *ListElement[Key, Value]
for {
for element := m.store.Load().item(hash); element != nil; element = element.Next() {
if element.keyHash == hash && element.key == key {
actual := element.Value()
return actual, true
}
if element.keyHash > hash {
break
}
}
if newElement == nil { // allocate only once
newElement = &ListElement[Key, Value]{
key: key,
keyHash: hash,
}
newElement.value.Store(&value)
}
if m.insertElement(newElement, hash, key, value) {
return value, false
}
}
}
// FillRate returns the fill rate of the map as a percentage integer.
func (m *Map[Key, Value]) FillRate() int {
store := m.store.Load()
count := int(store.count.Load())
l := len(store.index)
return (count * 100) / l
}
// Del deletes the key from the map and returns whether the key was deleted.
func (m *Map[Key, Value]) Del(key Key) bool {
hash := m.hasher(key)
store := m.store.Load()
element := store.item(hash)
for ; element != nil; element = element.Next() {
if element.keyHash == hash && element.key == key {
m.deleteElement(element)
m.linkedList.Delete(element)
return true
}
if element.keyHash > hash {
return false
}
}
return false
}
// Insert sets the value under the specified key to the map if it does not exist yet.
// If a resizing operation is happening concurrently while calling Insert, the item might show up in the map
// after the resize operation is finished.
// Returns true if the item was inserted or false if it existed.
func (m *Map[Key, Value]) Insert(key Key, value Value) bool {
hash := m.hasher(key)
var (
existed, inserted bool
element *ListElement[Key, Value]
)
for {
store := m.store.Load()
searchStart := store.item(hash)
if !inserted { // if retrying after insert during grow, do not add to list again
element, existed, inserted = m.linkedList.Add(searchStart, hash, key, value)
if existed {
return false
}
if !inserted {
continue // a concurrent add did interfere, try again
}
}
count := store.addItem(element)
currentStore := m.store.Load()
if store != currentStore { // retry insert in case of insert during grow
continue
}
if m.isResizeNeeded(store, count) && m.resizing.CompareAndSwap(0, 1) {
go m.grow(0, true)
}
return true
}
}
// Set sets the value under the specified key to the map. An existing item for this key will be overwritten.
// If a resizing operation is happening concurrently while calling Set, the item might show up in the map
// after the resize operation is finished.
func (m *Map[Key, Value]) Set(key Key, value Value) {
hash := m.hasher(key)
for {
store := m.store.Load()
searchStart := store.item(hash)
element, added := m.linkedList.AddOrUpdate(searchStart, hash, key, value)
if !added {
continue // a concurrent add did interfere, try again
}
count := store.addItem(element)
currentStore := m.store.Load()
if store != currentStore { // retry insert in case of insert during grow
continue
}
if m.isResizeNeeded(store, count) && m.resizing.CompareAndSwap(0, 1) {
go m.grow(0, true)
}
return
}
}
// Grow resizes the map to a new size, the size gets rounded up to next power of 2.
// To double the size of the map use newSize 0.
// This function returns immediately, the resize operation is done in a goroutine.
// No resizing is done in case of another resize operation already being in progress.
func (m *Map[Key, Value]) Grow(newSize uintptr) {
if m.resizing.CompareAndSwap(0, 1) {
go m.grow(newSize, true)
}
}
// String returns the map as a string, only hashed keys are printed.
func (m *Map[Key, Value]) String() string {
buffer := bytes.NewBufferString("")
buffer.WriteRune('[')
first := m.linkedList.First()
item := first
for item != nil {
if item != first {
buffer.WriteRune(',')
}
fmt.Fprint(buffer, item.keyHash)
item = item.Next()
}
buffer.WriteRune(']')
return buffer.String()
}
// Range calls f sequentially for each key and value present in the map.
// If f returns false, range stops the iteration.
func (m *Map[Key, Value]) Range(f func(Key, Value) bool) {
item := m.linkedList.First()
for item != nil {
value := item.Value()
if !f(item.key, value) {
return
}
item = item.Next()
}
}
func (m *Map[Key, Value]) allocate(newSize uintptr) {
m.linkedList = NewList[Key, Value]()
if m.resizing.CompareAndSwap(0, 1) {
m.grow(newSize, false)
}
}
func (m *Map[Key, Value]) isResizeNeeded(store *store[Key, Value], count uintptr) bool {
l := uintptr(len(store.index)) // l can't be 0 as it gets initialized in New()
fillRate := (count * 100) / l
return fillRate > maxFillRate
}
func (m *Map[Key, Value]) insertElement(element *ListElement[Key, Value], hash uintptr, key Key, value Value) bool {
var existed, inserted bool
for {
store := m.store.Load()
searchStart := store.item(element.keyHash)
if !inserted { // if retrying after insert during grow, do not add to list again
_, existed, inserted = m.linkedList.Add(searchStart, hash, key, value)
if existed {
return false
}
if !inserted {
continue // a concurrent add did interfere, try again
}
}
count := store.addItem(element)
currentStore := m.store.Load()
if store != currentStore { // retry insert in case of insert during grow
continue
}
if m.isResizeNeeded(store, count) && m.resizing.CompareAndSwap(0, 1) {
go m.grow(0, true)
}
return true
}
}
// deleteElement deletes an element from index.
func (m *Map[Key, Value]) deleteElement(element *ListElement[Key, Value]) {
for {
store := m.store.Load()
index := element.keyHash >> store.keyShifts
ptr := (*unsafe.Pointer)(unsafe.Pointer(uintptr(store.array) + index*intSizeBytes))
next := element.Next()
if next != nil && element.keyHash>>store.keyShifts != index {
next = nil // do not set index to next item if it's not the same slice index
}
atomic.CompareAndSwapPointer(ptr, unsafe.Pointer(element), unsafe.Pointer(next))
currentStore := m.store.Load()
if store == currentStore { // check that no resize happened
break
}
}
}
func (m *Map[Key, Value]) grow(newSize uintptr, loop bool) {
defer m.resizing.CompareAndSwap(1, 0)
for {
currentStore := m.store.Load()
if newSize == 0 {
newSize = uintptr(len(currentStore.index)) << 1
} else {
newSize = roundUpPower2(newSize)
}
index := make([]*ListElement[Key, Value], newSize)
header := (*reflect.SliceHeader)(unsafe.Pointer(&index))
newStore := &store[Key, Value]{
keyShifts: strconv.IntSize - log2(newSize),
array: unsafe.Pointer(header.Data), // use address of slice data storage
index: index,
}
m.fillIndexItems(newStore) // initialize new index slice with longer keys
m.store.Store(newStore)
m.fillIndexItems(newStore) // make sure that the new index is up-to-date with the current state of the linked list
if !loop {
return
}
// check if a new resize needs to be done already
count := uintptr(m.Len())
if !m.isResizeNeeded(newStore, count) {
return
}
newSize = 0 // 0 means double the current size
}
}
func (m *Map[Key, Value]) fillIndexItems(store *store[Key, Value]) {
first := m.linkedList.First()
item := first
lastIndex := uintptr(0)
for item != nil {
index := item.keyHash >> store.keyShifts
if item == first || index != lastIndex { // store item with smallest hash key for every index
store.addItem(item)
lastIndex = index
}
item = item.Next()
}
}