well-goknown/vendor/github.com/puzpuzpuz/xsync/v3/mapof.go

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package xsync
import (
"fmt"
"math"
"sync"
"sync/atomic"
"unsafe"
)
const (
// number of MapOf entries per bucket; 5 entries lead to size of 64B
// (one cache line) on 64-bit machines
entriesPerMapOfBucket = 5
defaultMeta uint64 = 0x8080808080808080
metaMask uint64 = 0xffffffffff
defaultMetaMasked uint64 = defaultMeta & metaMask
emptyMetaSlot uint8 = 0x80
)
// MapOf is like a Go map[K]V but is safe for concurrent
// use by multiple goroutines without additional locking or
// coordination. It follows the interface of sync.Map with
// a number of valuable extensions like Compute or Size.
//
// A MapOf must not be copied after first use.
//
// MapOf uses a modified version of Cache-Line Hash Table (CLHT)
// data structure: https://github.com/LPD-EPFL/CLHT
//
// CLHT is built around idea to organize the hash table in
// cache-line-sized buckets, so that on all modern CPUs update
// operations complete with at most one cache-line transfer.
// Also, Get operations involve no write to memory, as well as no
// mutexes or any other sort of locks. Due to this design, in all
// considered scenarios MapOf outperforms sync.Map.
//
// MapOf also borrows ideas from Java's j.u.c.ConcurrentHashMap
// (immutable K/V pair structs instead of atomic snapshots)
// and C++'s absl::flat_hash_map (meta memory and SWAR-based
// lookups).
type MapOf[K comparable, V any] struct {
totalGrowths int64
totalShrinks int64
resizing int64 // resize in progress flag; updated atomically
resizeMu sync.Mutex // only used along with resizeCond
resizeCond sync.Cond // used to wake up resize waiters (concurrent modifications)
table unsafe.Pointer // *mapOfTable
hasher func(K, uint64) uint64
minTableLen int
growOnly bool
}
type mapOfTable[K comparable, V any] struct {
buckets []bucketOfPadded
// striped counter for number of table entries;
// used to determine if a table shrinking is needed
// occupies min(buckets_memory/1024, 64KB) of memory
size []counterStripe
seed uint64
}
// bucketOfPadded is a CL-sized map bucket holding up to
// entriesPerMapOfBucket entries.
type bucketOfPadded struct {
//lint:ignore U1000 ensure each bucket takes two cache lines on both 32 and 64-bit archs
pad [cacheLineSize - unsafe.Sizeof(bucketOf{})]byte
bucketOf
}
type bucketOf struct {
meta uint64
entries [entriesPerMapOfBucket]unsafe.Pointer // *entryOf
next unsafe.Pointer // *bucketOfPadded
mu sync.Mutex
}
// entryOf is an immutable map entry.
type entryOf[K comparable, V any] struct {
key K
value V
}
// NewMapOf creates a new MapOf instance configured with the given
// options.
func NewMapOf[K comparable, V any](options ...func(*MapConfig)) *MapOf[K, V] {
return NewMapOfWithHasher[K, V](defaultHasher[K](), options...)
}
// NewMapOfWithHasher creates a new MapOf instance configured with
// the given hasher and options. The hash function is used instead
// of the built-in hash function configured when a map is created
// with the NewMapOf function.
func NewMapOfWithHasher[K comparable, V any](
hasher func(K, uint64) uint64,
options ...func(*MapConfig),
) *MapOf[K, V] {
c := &MapConfig{
sizeHint: defaultMinMapTableLen * entriesPerMapOfBucket,
}
for _, o := range options {
o(c)
}
m := &MapOf[K, V]{}
m.resizeCond = *sync.NewCond(&m.resizeMu)
m.hasher = hasher
var table *mapOfTable[K, V]
if c.sizeHint <= defaultMinMapTableLen*entriesPerMapOfBucket {
table = newMapOfTable[K, V](defaultMinMapTableLen)
} else {
tableLen := nextPowOf2(uint32((float64(c.sizeHint) / entriesPerMapOfBucket) / mapLoadFactor))
table = newMapOfTable[K, V](int(tableLen))
}
m.minTableLen = len(table.buckets)
m.growOnly = c.growOnly
atomic.StorePointer(&m.table, unsafe.Pointer(table))
return m
}
// NewMapOfPresized creates a new MapOf instance with capacity enough
// to hold sizeHint entries. The capacity is treated as the minimal capacity
// meaning that the underlying hash table will never shrink to
// a smaller capacity. If sizeHint is zero or negative, the value
// is ignored.
//
// Deprecated: use NewMapOf in combination with WithPresize.
func NewMapOfPresized[K comparable, V any](sizeHint int) *MapOf[K, V] {
return NewMapOf[K, V](WithPresize(sizeHint))
}
func newMapOfTable[K comparable, V any](minTableLen int) *mapOfTable[K, V] {
buckets := make([]bucketOfPadded, minTableLen)
for i := range buckets {
buckets[i].meta = defaultMeta
}
counterLen := minTableLen >> 10
if counterLen < minMapCounterLen {
counterLen = minMapCounterLen
} else if counterLen > maxMapCounterLen {
counterLen = maxMapCounterLen
}
counter := make([]counterStripe, counterLen)
t := &mapOfTable[K, V]{
buckets: buckets,
size: counter,
seed: makeSeed(),
}
return t
}
// Load returns the value stored in the map for a key, or zero value
// of type V if no value is present.
// The ok result indicates whether value was found in the map.
func (m *MapOf[K, V]) Load(key K) (value V, ok bool) {
table := (*mapOfTable[K, V])(atomic.LoadPointer(&m.table))
hash := m.hasher(key, table.seed)
h1 := h1(hash)
h2w := broadcast(h2(hash))
bidx := uint64(len(table.buckets)-1) & h1
b := &table.buckets[bidx]
for {
metaw := atomic.LoadUint64(&b.meta)
markedw := markZeroBytes(metaw^h2w) & metaMask
for markedw != 0 {
idx := firstMarkedByteIndex(markedw)
eptr := atomic.LoadPointer(&b.entries[idx])
if eptr != nil {
e := (*entryOf[K, V])(eptr)
if e.key == key {
return e.value, true
}
}
markedw &= markedw - 1
}
bptr := atomic.LoadPointer(&b.next)
if bptr == nil {
return
}
b = (*bucketOfPadded)(bptr)
}
}
// Store sets the value for a key.
func (m *MapOf[K, V]) Store(key K, value V) {
m.doCompute(
key,
func(V, bool) (V, bool) {
return value, false
},
false,
false,
)
}
// LoadOrStore returns the existing value for the key if present.
// Otherwise, it stores and returns the given value.
// The loaded result is true if the value was loaded, false if stored.
func (m *MapOf[K, V]) LoadOrStore(key K, value V) (actual V, loaded bool) {
return m.doCompute(
key,
func(V, bool) (V, bool) {
return value, false
},
true,
false,
)
}
// LoadAndStore returns the existing value for the key if present,
// while setting the new value for the key.
// It stores the new value and returns the existing one, if present.
// The loaded result is true if the existing value was loaded,
// false otherwise.
func (m *MapOf[K, V]) LoadAndStore(key K, value V) (actual V, loaded bool) {
return m.doCompute(
key,
func(V, bool) (V, bool) {
return value, false
},
false,
false,
)
}
// LoadOrCompute returns the existing value for the key if present.
// Otherwise, it computes the value using the provided function and
// returns the computed value. The loaded result is true if the value
// was loaded, false if stored.
//
// This call locks a hash table bucket while the compute function
// is executed. It means that modifications on other entries in
// the bucket will be blocked until the valueFn executes. Consider
// this when the function includes long-running operations.
func (m *MapOf[K, V]) LoadOrCompute(key K, valueFn func() V) (actual V, loaded bool) {
return m.doCompute(
key,
func(V, bool) (V, bool) {
return valueFn(), false
},
true,
false,
)
}
// Compute either sets the computed new value for the key or deletes
// the value for the key. When the delete result of the valueFn function
// is set to true, the value will be deleted, if it exists. When delete
// is set to false, the value is updated to the newValue.
// The ok result indicates whether value was computed and stored, thus, is
// present in the map. The actual result contains the new value in cases where
// the value was computed and stored. See the example for a few use cases.
//
// This call locks a hash table bucket while the compute function
// is executed. It means that modifications on other entries in
// the bucket will be blocked until the valueFn executes. Consider
// this when the function includes long-running operations.
func (m *MapOf[K, V]) Compute(
key K,
valueFn func(oldValue V, loaded bool) (newValue V, delete bool),
) (actual V, ok bool) {
return m.doCompute(key, valueFn, false, true)
}
// LoadAndDelete deletes the value for a key, returning the previous
// value if any. The loaded result reports whether the key was
// present.
func (m *MapOf[K, V]) LoadAndDelete(key K) (value V, loaded bool) {
return m.doCompute(
key,
func(value V, loaded bool) (V, bool) {
return value, true
},
false,
false,
)
}
// Delete deletes the value for a key.
func (m *MapOf[K, V]) Delete(key K) {
m.doCompute(
key,
func(value V, loaded bool) (V, bool) {
return value, true
},
false,
false,
)
}
func (m *MapOf[K, V]) doCompute(
key K,
valueFn func(oldValue V, loaded bool) (V, bool),
loadIfExists, computeOnly bool,
) (V, bool) {
// Read-only path.
if loadIfExists {
if v, ok := m.Load(key); ok {
return v, !computeOnly
}
}
// Write path.
for {
compute_attempt:
var (
emptyb *bucketOfPadded
emptyidx int
)
table := (*mapOfTable[K, V])(atomic.LoadPointer(&m.table))
tableLen := len(table.buckets)
hash := m.hasher(key, table.seed)
h1 := h1(hash)
h2 := h2(hash)
h2w := broadcast(h2)
bidx := uint64(len(table.buckets)-1) & h1
rootb := &table.buckets[bidx]
rootb.mu.Lock()
// The following two checks must go in reverse to what's
// in the resize method.
if m.resizeInProgress() {
// Resize is in progress. Wait, then go for another attempt.
rootb.mu.Unlock()
m.waitForResize()
goto compute_attempt
}
if m.newerTableExists(table) {
// Someone resized the table. Go for another attempt.
rootb.mu.Unlock()
goto compute_attempt
}
b := rootb
for {
metaw := b.meta
markedw := markZeroBytes(metaw^h2w) & metaMask
for markedw != 0 {
idx := firstMarkedByteIndex(markedw)
eptr := b.entries[idx]
if eptr != nil {
e := (*entryOf[K, V])(eptr)
if e.key == key {
if loadIfExists {
rootb.mu.Unlock()
return e.value, !computeOnly
}
// In-place update/delete.
// We get a copy of the value via an interface{} on each call,
// thus the live value pointers are unique. Otherwise atomic
// snapshot won't be correct in case of multiple Store calls
// using the same value.
oldv := e.value
newv, del := valueFn(oldv, true)
if del {
// Deletion.
// First we update the hash, then the entry.
newmetaw := setByte(metaw, emptyMetaSlot, idx)
atomic.StoreUint64(&b.meta, newmetaw)
atomic.StorePointer(&b.entries[idx], nil)
rootb.mu.Unlock()
table.addSize(bidx, -1)
// Might need to shrink the table if we left bucket empty.
if newmetaw == defaultMeta {
m.resize(table, mapShrinkHint)
}
return oldv, !computeOnly
}
newe := new(entryOf[K, V])
newe.key = key
newe.value = newv
atomic.StorePointer(&b.entries[idx], unsafe.Pointer(newe))
rootb.mu.Unlock()
if computeOnly {
// Compute expects the new value to be returned.
return newv, true
}
// LoadAndStore expects the old value to be returned.
return oldv, true
}
}
markedw &= markedw - 1
}
if emptyb == nil {
// Search for empty entries (up to 5 per bucket).
emptyw := metaw & defaultMetaMasked
if emptyw != 0 {
idx := firstMarkedByteIndex(emptyw)
emptyb = b
emptyidx = idx
}
}
if b.next == nil {
if emptyb != nil {
// Insertion into an existing bucket.
var zeroedV V
newValue, del := valueFn(zeroedV, false)
if del {
rootb.mu.Unlock()
return zeroedV, false
}
newe := new(entryOf[K, V])
newe.key = key
newe.value = newValue
// First we update meta, then the entry.
atomic.StoreUint64(&emptyb.meta, setByte(emptyb.meta, h2, emptyidx))
atomic.StorePointer(&emptyb.entries[emptyidx], unsafe.Pointer(newe))
rootb.mu.Unlock()
table.addSize(bidx, 1)
return newValue, computeOnly
}
growThreshold := float64(tableLen) * entriesPerMapOfBucket * mapLoadFactor
if table.sumSize() > int64(growThreshold) {
// Need to grow the table. Then go for another attempt.
rootb.mu.Unlock()
m.resize(table, mapGrowHint)
goto compute_attempt
}
// Insertion into a new bucket.
var zeroedV V
newValue, del := valueFn(zeroedV, false)
if del {
rootb.mu.Unlock()
return newValue, false
}
// Create and append a bucket.
newb := new(bucketOfPadded)
newb.meta = setByte(defaultMeta, h2, 0)
newe := new(entryOf[K, V])
newe.key = key
newe.value = newValue
newb.entries[0] = unsafe.Pointer(newe)
atomic.StorePointer(&b.next, unsafe.Pointer(newb))
rootb.mu.Unlock()
table.addSize(bidx, 1)
return newValue, computeOnly
}
b = (*bucketOfPadded)(b.next)
}
}
}
func (m *MapOf[K, V]) newerTableExists(table *mapOfTable[K, V]) bool {
curTablePtr := atomic.LoadPointer(&m.table)
return uintptr(curTablePtr) != uintptr(unsafe.Pointer(table))
}
func (m *MapOf[K, V]) resizeInProgress() bool {
return atomic.LoadInt64(&m.resizing) == 1
}
func (m *MapOf[K, V]) waitForResize() {
m.resizeMu.Lock()
for m.resizeInProgress() {
m.resizeCond.Wait()
}
m.resizeMu.Unlock()
}
func (m *MapOf[K, V]) resize(knownTable *mapOfTable[K, V], hint mapResizeHint) {
knownTableLen := len(knownTable.buckets)
// Fast path for shrink attempts.
if hint == mapShrinkHint {
if m.growOnly ||
m.minTableLen == knownTableLen ||
knownTable.sumSize() > int64((knownTableLen*entriesPerMapOfBucket)/mapShrinkFraction) {
return
}
}
// Slow path.
if !atomic.CompareAndSwapInt64(&m.resizing, 0, 1) {
// Someone else started resize. Wait for it to finish.
m.waitForResize()
return
}
var newTable *mapOfTable[K, V]
table := (*mapOfTable[K, V])(atomic.LoadPointer(&m.table))
tableLen := len(table.buckets)
switch hint {
case mapGrowHint:
// Grow the table with factor of 2.
atomic.AddInt64(&m.totalGrowths, 1)
newTable = newMapOfTable[K, V](tableLen << 1)
case mapShrinkHint:
shrinkThreshold := int64((tableLen * entriesPerMapOfBucket) / mapShrinkFraction)
if tableLen > m.minTableLen && table.sumSize() <= shrinkThreshold {
// Shrink the table with factor of 2.
atomic.AddInt64(&m.totalShrinks, 1)
newTable = newMapOfTable[K, V](tableLen >> 1)
} else {
// No need to shrink. Wake up all waiters and give up.
m.resizeMu.Lock()
atomic.StoreInt64(&m.resizing, 0)
m.resizeCond.Broadcast()
m.resizeMu.Unlock()
return
}
case mapClearHint:
newTable = newMapOfTable[K, V](m.minTableLen)
default:
panic(fmt.Sprintf("unexpected resize hint: %d", hint))
}
// Copy the data only if we're not clearing the map.
if hint != mapClearHint {
for i := 0; i < tableLen; i++ {
copied := copyBucketOf(&table.buckets[i], newTable, m.hasher)
newTable.addSizePlain(uint64(i), copied)
}
}
// Publish the new table and wake up all waiters.
atomic.StorePointer(&m.table, unsafe.Pointer(newTable))
m.resizeMu.Lock()
atomic.StoreInt64(&m.resizing, 0)
m.resizeCond.Broadcast()
m.resizeMu.Unlock()
}
func copyBucketOf[K comparable, V any](
b *bucketOfPadded,
destTable *mapOfTable[K, V],
hasher func(K, uint64) uint64,
) (copied int) {
rootb := b
rootb.mu.Lock()
for {
for i := 0; i < entriesPerMapOfBucket; i++ {
if b.entries[i] != nil {
e := (*entryOf[K, V])(b.entries[i])
hash := hasher(e.key, destTable.seed)
bidx := uint64(len(destTable.buckets)-1) & h1(hash)
destb := &destTable.buckets[bidx]
appendToBucketOf(h2(hash), b.entries[i], destb)
copied++
}
}
if b.next == nil {
rootb.mu.Unlock()
return
}
b = (*bucketOfPadded)(b.next)
}
}
// Range calls f sequentially for each key and value present in the
// map. If f returns false, range stops the iteration.
//
// Range does not necessarily correspond to any consistent snapshot
// of the Map's contents: no key will be visited more than once, but
// if the value for any key is stored or deleted concurrently, Range
// may reflect any mapping for that key from any point during the
// Range call.
//
// It is safe to modify the map while iterating it, including entry
// creation, modification and deletion. However, the concurrent
// modification rule apply, i.e. the changes may be not reflected
// in the subsequently iterated entries.
func (m *MapOf[K, V]) Range(f func(key K, value V) bool) {
var zeroPtr unsafe.Pointer
// Pre-allocate array big enough to fit entries for most hash tables.
bentries := make([]unsafe.Pointer, 0, 16*entriesPerMapOfBucket)
tablep := atomic.LoadPointer(&m.table)
table := *(*mapOfTable[K, V])(tablep)
for i := range table.buckets {
rootb := &table.buckets[i]
b := rootb
// Prevent concurrent modifications and copy all entries into
// the intermediate slice.
rootb.mu.Lock()
for {
for i := 0; i < entriesPerMapOfBucket; i++ {
if b.entries[i] != nil {
bentries = append(bentries, b.entries[i])
}
}
if b.next == nil {
rootb.mu.Unlock()
break
}
b = (*bucketOfPadded)(b.next)
}
// Call the function for all copied entries.
for j := range bentries {
entry := (*entryOf[K, V])(bentries[j])
if !f(entry.key, entry.value) {
return
}
// Remove the reference to avoid preventing the copied
// entries from being GCed until this method finishes.
bentries[j] = zeroPtr
}
bentries = bentries[:0]
}
}
// Clear deletes all keys and values currently stored in the map.
func (m *MapOf[K, V]) Clear() {
table := (*mapOfTable[K, V])(atomic.LoadPointer(&m.table))
m.resize(table, mapClearHint)
}
// Size returns current size of the map.
func (m *MapOf[K, V]) Size() int {
table := (*mapOfTable[K, V])(atomic.LoadPointer(&m.table))
return int(table.sumSize())
}
func appendToBucketOf(h2 uint8, entryPtr unsafe.Pointer, b *bucketOfPadded) {
for {
for i := 0; i < entriesPerMapOfBucket; i++ {
if b.entries[i] == nil {
b.meta = setByte(b.meta, h2, i)
b.entries[i] = entryPtr
return
}
}
if b.next == nil {
newb := new(bucketOfPadded)
newb.meta = setByte(defaultMeta, h2, 0)
newb.entries[0] = entryPtr
b.next = unsafe.Pointer(newb)
return
}
b = (*bucketOfPadded)(b.next)
}
}
func (table *mapOfTable[K, V]) addSize(bucketIdx uint64, delta int) {
cidx := uint64(len(table.size)-1) & bucketIdx
atomic.AddInt64(&table.size[cidx].c, int64(delta))
}
func (table *mapOfTable[K, V]) addSizePlain(bucketIdx uint64, delta int) {
cidx := uint64(len(table.size)-1) & bucketIdx
table.size[cidx].c += int64(delta)
}
func (table *mapOfTable[K, V]) sumSize() int64 {
sum := int64(0)
for i := range table.size {
sum += atomic.LoadInt64(&table.size[i].c)
}
return sum
}
func h1(h uint64) uint64 {
return h >> 7
}
func h2(h uint64) uint8 {
return uint8(h & 0x7f)
}
// Stats returns statistics for the MapOf. Just like other map
// methods, this one is thread-safe. Yet it's an O(N) operation,
// so it should be used only for diagnostics or debugging purposes.
func (m *MapOf[K, V]) Stats() MapStats {
stats := MapStats{
TotalGrowths: atomic.LoadInt64(&m.totalGrowths),
TotalShrinks: atomic.LoadInt64(&m.totalShrinks),
MinEntries: math.MaxInt32,
}
table := (*mapOfTable[K, V])(atomic.LoadPointer(&m.table))
stats.RootBuckets = len(table.buckets)
stats.Counter = int(table.sumSize())
stats.CounterLen = len(table.size)
for i := range table.buckets {
nentries := 0
b := &table.buckets[i]
stats.TotalBuckets++
for {
nentriesLocal := 0
stats.Capacity += entriesPerMapOfBucket
for i := 0; i < entriesPerMapOfBucket; i++ {
if atomic.LoadPointer(&b.entries[i]) != nil {
stats.Size++
nentriesLocal++
}
}
nentries += nentriesLocal
if nentriesLocal == 0 {
stats.EmptyBuckets++
}
if b.next == nil {
break
}
b = (*bucketOfPadded)(atomic.LoadPointer(&b.next))
stats.TotalBuckets++
}
if nentries < stats.MinEntries {
stats.MinEntries = nentries
}
if nentries > stats.MaxEntries {
stats.MaxEntries = nentries
}
}
return stats
}