+++ /dev/null
-// Copyright 2024 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-//go:build goexperiment.synchashtriemap
-
-package sync
-
-import (
- isync "internal/sync"
-)
-
-// Map is like a Go map[any]any but is safe for concurrent use
-// by multiple goroutines without additional locking or coordination.
-// Loads, stores, and deletes run in amortized constant time.
-//
-// The Map type is specialized. Most code should use a plain Go map instead,
-// with separate locking or coordination, for better type safety and to make it
-// easier to maintain other invariants along with the map content.
-//
-// The Map type is optimized for two common use cases: (1) when the entry for a given
-// key is only ever written once but read many times, as in caches that only grow,
-// or (2) when multiple goroutines read, write, and overwrite entries for disjoint
-// sets of keys. In these two cases, use of a Map may significantly reduce lock
-// contention compared to a Go map paired with a separate [Mutex] or [RWMutex].
-//
-// The zero Map is empty and ready for use. A Map must not be copied after first use.
-//
-// In the terminology of [the Go memory model], Map arranges that a write operation
-// “synchronizes before” any read operation that observes the effect of the write, where
-// read and write operations are defined as follows.
-// [Map.Load], [Map.LoadAndDelete], [Map.LoadOrStore], [Map.Swap], [Map.CompareAndSwap],
-// and [Map.CompareAndDelete] are read operations;
-// [Map.Delete], [Map.LoadAndDelete], [Map.Store], and [Map.Swap] are write operations;
-// [Map.LoadOrStore] is a write operation when it returns loaded set to false;
-// [Map.CompareAndSwap] is a write operation when it returns swapped set to true;
-// and [Map.CompareAndDelete] is a write operation when it returns deleted set to true.
-//
-// [the Go memory model]: https://go.dev/ref/mem
-type Map struct {
- _ noCopy
-
- m isync.HashTrieMap[any, any]
-}
-
-// Load returns the value stored in the map for a key, or nil if no
-// value is present.
-// The ok result indicates whether value was found in the map.
-func (m *Map) Load(key any) (value any, ok bool) {
- return m.m.Load(key)
-}
-
-// Store sets the value for a key.
-func (m *Map) Store(key, value any) {
- m.m.Store(key, value)
-}
-
-// Clear deletes all the entries, resulting in an empty Map.
-func (m *Map) Clear() {
- m.m.Clear()
-}
-
-// 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 *Map) LoadOrStore(key, value any) (actual any, loaded bool) {
- return m.m.LoadOrStore(key, value)
-}
-
-// LoadAndDelete deletes the value for a key, returning the previous value if any.
-// The loaded result reports whether the key was present.
-func (m *Map) LoadAndDelete(key any) (value any, loaded bool) {
- return m.m.LoadAndDelete(key)
-}
-
-// Delete deletes the value for a key.
-// If the key is not in the map, Delete does nothing.
-func (m *Map) Delete(key any) {
- m.m.Delete(key)
-}
-
-// Swap swaps the value for a key and returns the previous value if any.
-// The loaded result reports whether the key was present.
-func (m *Map) Swap(key, value any) (previous any, loaded bool) {
- return m.m.Swap(key, value)
-}
-
-// CompareAndSwap swaps the old and new values for key
-// if the value stored in the map is equal to old.
-// The old value must be of a comparable type.
-func (m *Map) CompareAndSwap(key, old, new any) (swapped bool) {
- return m.m.CompareAndSwap(key, old, new)
-}
-
-// CompareAndDelete deletes the entry for key if its value is equal to old.
-// The old value must be of a comparable type.
-//
-// If there is no current value for key in the map, CompareAndDelete
-// returns false (even if the old value is the nil interface value).
-func (m *Map) CompareAndDelete(key, old any) (deleted bool) {
- return m.m.CompareAndDelete(key, old)
-}
-
-// 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 (including by f), Range may reflect any
-// mapping for that key from any point during the Range call. Range does not
-// block other methods on the receiver; even f itself may call any method on m.
-//
-// Range may be O(N) with the number of elements in the map even if f returns
-// false after a constant number of calls.
-func (m *Map) Range(f func(key, value any) bool) {
- m.m.Range(f)
-}
-// Copyright 2016 The Go Authors. All rights reserved.
+// Copyright 2024 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
-//go:build !goexperiment.synchashtriemap
-
package sync
import (
- "sync/atomic"
+ isync "internal/sync"
)
// Map is like a Go map[any]any but is safe for concurrent use
type Map struct {
_ noCopy
- mu Mutex
-
- // read contains the portion of the map's contents that are safe for
- // concurrent access (with or without mu held).
- //
- // The read field itself is always safe to load, but must only be stored with
- // mu held.
- //
- // Entries stored in read may be updated concurrently without mu, but updating
- // a previously-expunged entry requires that the entry be copied to the dirty
- // map and unexpunged with mu held.
- read atomic.Pointer[readOnly]
-
- // dirty contains the portion of the map's contents that require mu to be
- // held. To ensure that the dirty map can be promoted to the read map quickly,
- // it also includes all of the non-expunged entries in the read map.
- //
- // Expunged entries are not stored in the dirty map. An expunged entry in the
- // clean map must be unexpunged and added to the dirty map before a new value
- // can be stored to it.
- //
- // If the dirty map is nil, the next write to the map will initialize it by
- // making a shallow copy of the clean map, omitting stale entries.
- dirty map[any]*entry
-
- // misses counts the number of loads since the read map was last updated that
- // needed to lock mu to determine whether the key was present.
- //
- // Once enough misses have occurred to cover the cost of copying the dirty
- // map, the dirty map will be promoted to the read map (in the unamended
- // state) and the next store to the map will make a new dirty copy.
- misses int
-}
-
-// readOnly is an immutable struct stored atomically in the Map.read field.
-type readOnly struct {
- m map[any]*entry
- amended bool // true if the dirty map contains some key not in m.
-}
-
-// expunged is an arbitrary pointer that marks entries which have been deleted
-// from the dirty map.
-var expunged = new(any)
-
-// An entry is a slot in the map corresponding to a particular key.
-type entry struct {
- // p points to the interface{} value stored for the entry.
- //
- // If p == nil, the entry has been deleted, and either m.dirty == nil or
- // m.dirty[key] is e.
- //
- // If p == expunged, the entry has been deleted, m.dirty != nil, and the entry
- // is missing from m.dirty.
- //
- // Otherwise, the entry is valid and recorded in m.read.m[key] and, if m.dirty
- // != nil, in m.dirty[key].
- //
- // An entry can be deleted by atomic replacement with nil: when m.dirty is
- // next created, it will atomically replace nil with expunged and leave
- // m.dirty[key] unset.
- //
- // An entry's associated value can be updated by atomic replacement, provided
- // p != expunged. If p == expunged, an entry's associated value can be updated
- // only after first setting m.dirty[key] = e so that lookups using the dirty
- // map find the entry.
- p atomic.Pointer[any]
-}
-
-func newEntry(i any) *entry {
- e := &entry{}
- e.p.Store(&i)
- return e
-}
-
-func (m *Map) loadReadOnly() readOnly {
- if p := m.read.Load(); p != nil {
- return *p
- }
- return readOnly{}
+ m isync.HashTrieMap[any, any]
}
// Load returns the value stored in the map for a key, or nil if no
// value is present.
// The ok result indicates whether value was found in the map.
func (m *Map) Load(key any) (value any, ok bool) {
- read := m.loadReadOnly()
- e, ok := read.m[key]
- if !ok && read.amended {
- m.mu.Lock()
- // Avoid reporting a spurious miss if m.dirty got promoted while we were
- // blocked on m.mu. (If further loads of the same key will not miss, it's
- // not worth copying the dirty map for this key.)
- read = m.loadReadOnly()
- e, ok = read.m[key]
- if !ok && read.amended {
- e, ok = m.dirty[key]
- // Regardless of whether the entry was present, record a miss: this key
- // will take the slow path until the dirty map is promoted to the read
- // map.
- m.missLocked()
- }
- m.mu.Unlock()
- }
- if !ok {
- return nil, false
- }
- return e.load()
-}
-
-func (e *entry) load() (value any, ok bool) {
- p := e.p.Load()
- if p == nil || p == expunged {
- return nil, false
- }
- return *p, true
+ return m.m.Load(key)
}
// Store sets the value for a key.
func (m *Map) Store(key, value any) {
- _, _ = m.Swap(key, value)
+ m.m.Store(key, value)
}
// Clear deletes all the entries, resulting in an empty Map.
func (m *Map) Clear() {
- read := m.loadReadOnly()
- if len(read.m) == 0 && !read.amended {
- // Avoid allocating a new readOnly when the map is already clear.
- return
- }
-
- m.mu.Lock()
- defer m.mu.Unlock()
-
- read = m.loadReadOnly()
- if len(read.m) > 0 || read.amended {
- m.read.Store(&readOnly{})
- }
-
- clear(m.dirty)
- // Don't immediately promote the newly-cleared dirty map on the next operation.
- m.misses = 0
-}
-
-// tryCompareAndSwap compare the entry with the given old value and swaps
-// it with a new value if the entry is equal to the old value, and the entry
-// has not been expunged.
-//
-// If the entry is expunged, tryCompareAndSwap returns false and leaves
-// the entry unchanged.
-func (e *entry) tryCompareAndSwap(old, new any) bool {
- p := e.p.Load()
- if p == nil || p == expunged || *p != old {
- return false
- }
-
- // Copy the interface after the first load to make this method more amenable
- // to escape analysis: if the comparison fails from the start, we shouldn't
- // bother heap-allocating an interface value to store.
- nc := new
- for {
- if e.p.CompareAndSwap(p, &nc) {
- return true
- }
- p = e.p.Load()
- if p == nil || p == expunged || *p != old {
- return false
- }
- }
-}
-
-// unexpungeLocked ensures that the entry is not marked as expunged.
-//
-// If the entry was previously expunged, it must be added to the dirty map
-// before m.mu is unlocked.
-func (e *entry) unexpungeLocked() (wasExpunged bool) {
- return e.p.CompareAndSwap(expunged, nil)
-}
-
-// swapLocked unconditionally swaps a value into the entry.
-//
-// The entry must be known not to be expunged.
-func (e *entry) swapLocked(i *any) *any {
- return e.p.Swap(i)
+ m.m.Clear()
}
// 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 *Map) LoadOrStore(key, value any) (actual any, loaded bool) {
- // Avoid locking if it's a clean hit.
- read := m.loadReadOnly()
- if e, ok := read.m[key]; ok {
- actual, loaded, ok := e.tryLoadOrStore(value)
- if ok {
- return actual, loaded
- }
- }
-
- m.mu.Lock()
- read = m.loadReadOnly()
- if e, ok := read.m[key]; ok {
- if e.unexpungeLocked() {
- m.dirty[key] = e
- }
- actual, loaded, _ = e.tryLoadOrStore(value)
- } else if e, ok := m.dirty[key]; ok {
- actual, loaded, _ = e.tryLoadOrStore(value)
- m.missLocked()
- } else {
- if !read.amended {
- // We're adding the first new key to the dirty map.
- // Make sure it is allocated and mark the read-only map as incomplete.
- m.dirtyLocked()
- m.read.Store(&readOnly{m: read.m, amended: true})
- }
- m.dirty[key] = newEntry(value)
- actual, loaded = value, false
- }
- m.mu.Unlock()
-
- return actual, loaded
-}
-
-// tryLoadOrStore atomically loads or stores a value if the entry is not
-// expunged.
-//
-// If the entry is expunged, tryLoadOrStore leaves the entry unchanged and
-// returns with ok==false.
-func (e *entry) tryLoadOrStore(i any) (actual any, loaded, ok bool) {
- p := e.p.Load()
- if p == expunged {
- return nil, false, false
- }
- if p != nil {
- return *p, true, true
- }
-
- // Copy the interface after the first load to make this method more amenable
- // to escape analysis: if we hit the "load" path or the entry is expunged, we
- // shouldn't bother heap-allocating.
- ic := i
- for {
- if e.p.CompareAndSwap(nil, &ic) {
- return i, false, true
- }
- p = e.p.Load()
- if p == expunged {
- return nil, false, false
- }
- if p != nil {
- return *p, true, true
- }
- }
+ return m.m.LoadOrStore(key, value)
}
// LoadAndDelete deletes the value for a key, returning the previous value if any.
// The loaded result reports whether the key was present.
func (m *Map) LoadAndDelete(key any) (value any, loaded bool) {
- read := m.loadReadOnly()
- e, ok := read.m[key]
- if !ok && read.amended {
- m.mu.Lock()
- read = m.loadReadOnly()
- e, ok = read.m[key]
- if !ok && read.amended {
- e, ok = m.dirty[key]
- delete(m.dirty, key)
- // Regardless of whether the entry was present, record a miss: this key
- // will take the slow path until the dirty map is promoted to the read
- // map.
- m.missLocked()
- }
- m.mu.Unlock()
- }
- if ok {
- return e.delete()
- }
- return nil, false
+ return m.m.LoadAndDelete(key)
}
// Delete deletes the value for a key.
+// If the key is not in the map, Delete does nothing.
func (m *Map) Delete(key any) {
- m.LoadAndDelete(key)
-}
-
-func (e *entry) delete() (value any, ok bool) {
- for {
- p := e.p.Load()
- if p == nil || p == expunged {
- return nil, false
- }
- if e.p.CompareAndSwap(p, nil) {
- return *p, true
- }
- }
-}
-
-// trySwap swaps a value if the entry has not been expunged.
-//
-// If the entry is expunged, trySwap returns false and leaves the entry
-// unchanged.
-func (e *entry) trySwap(i *any) (*any, bool) {
- for {
- p := e.p.Load()
- if p == expunged {
- return nil, false
- }
- if e.p.CompareAndSwap(p, i) {
- return p, true
- }
- }
+ m.m.Delete(key)
}
// Swap swaps the value for a key and returns the previous value if any.
// The loaded result reports whether the key was present.
func (m *Map) Swap(key, value any) (previous any, loaded bool) {
- read := m.loadReadOnly()
- if e, ok := read.m[key]; ok {
- if v, ok := e.trySwap(&value); ok {
- if v == nil {
- return nil, false
- }
- return *v, true
- }
- }
-
- m.mu.Lock()
- read = m.loadReadOnly()
- if e, ok := read.m[key]; ok {
- if e.unexpungeLocked() {
- // The entry was previously expunged, which implies that there is a
- // non-nil dirty map and this entry is not in it.
- m.dirty[key] = e
- }
- if v := e.swapLocked(&value); v != nil {
- loaded = true
- previous = *v
- }
- } else if e, ok := m.dirty[key]; ok {
- if v := e.swapLocked(&value); v != nil {
- loaded = true
- previous = *v
- }
- } else {
- if !read.amended {
- // We're adding the first new key to the dirty map.
- // Make sure it is allocated and mark the read-only map as incomplete.
- m.dirtyLocked()
- m.read.Store(&readOnly{m: read.m, amended: true})
- }
- m.dirty[key] = newEntry(value)
- }
- m.mu.Unlock()
- return previous, loaded
+ return m.m.Swap(key, value)
}
// CompareAndSwap swaps the old and new values for key
// if the value stored in the map is equal to old.
// The old value must be of a comparable type.
func (m *Map) CompareAndSwap(key, old, new any) (swapped bool) {
- read := m.loadReadOnly()
- if e, ok := read.m[key]; ok {
- return e.tryCompareAndSwap(old, new)
- } else if !read.amended {
- return false // No existing value for key.
- }
-
- m.mu.Lock()
- defer m.mu.Unlock()
- read = m.loadReadOnly()
- swapped = false
- if e, ok := read.m[key]; ok {
- swapped = e.tryCompareAndSwap(old, new)
- } else if e, ok := m.dirty[key]; ok {
- swapped = e.tryCompareAndSwap(old, new)
- // We needed to lock mu in order to load the entry for key,
- // and the operation didn't change the set of keys in the map
- // (so it would be made more efficient by promoting the dirty
- // map to read-only).
- // Count it as a miss so that we will eventually switch to the
- // more efficient steady state.
- m.missLocked()
- }
- return swapped
+ return m.m.CompareAndSwap(key, old, new)
}
// CompareAndDelete deletes the entry for key if its value is equal to old.
// If there is no current value for key in the map, CompareAndDelete
// returns false (even if the old value is the nil interface value).
func (m *Map) CompareAndDelete(key, old any) (deleted bool) {
- read := m.loadReadOnly()
- e, ok := read.m[key]
- if !ok && read.amended {
- m.mu.Lock()
- read = m.loadReadOnly()
- e, ok = read.m[key]
- if !ok && read.amended {
- e, ok = m.dirty[key]
- // Don't delete key from m.dirty: we still need to do the “compare” part
- // of the operation. The entry will eventually be expunged when the
- // dirty map is promoted to the read map.
- //
- // Regardless of whether the entry was present, record a miss: this key
- // will take the slow path until the dirty map is promoted to the read
- // map.
- m.missLocked()
- }
- m.mu.Unlock()
- }
- for ok {
- p := e.p.Load()
- if p == nil || p == expunged || *p != old {
- return false
- }
- if e.p.CompareAndSwap(p, nil) {
- return true
- }
- }
- return false
+ return m.m.CompareAndDelete(key, old)
}
// Range calls f sequentially for each key and value present in the map.
// Range may be O(N) with the number of elements in the map even if f returns
// false after a constant number of calls.
func (m *Map) Range(f func(key, value any) bool) {
- // We need to be able to iterate over all of the keys that were already
- // present at the start of the call to Range.
- // If read.amended is false, then read.m satisfies that property without
- // requiring us to hold m.mu for a long time.
- read := m.loadReadOnly()
- if read.amended {
- // m.dirty contains keys not in read.m. Fortunately, Range is already O(N)
- // (assuming the caller does not break out early), so a call to Range
- // amortizes an entire copy of the map: we can promote the dirty copy
- // immediately!
- m.mu.Lock()
- read = m.loadReadOnly()
- if read.amended {
- read = readOnly{m: m.dirty}
- copyRead := read
- m.read.Store(©Read)
- m.dirty = nil
- m.misses = 0
- }
- m.mu.Unlock()
- }
-
- for k, e := range read.m {
- v, ok := e.load()
- if !ok {
- continue
- }
- if !f(k, v) {
- break
- }
- }
-}
-
-func (m *Map) missLocked() {
- m.misses++
- if m.misses < len(m.dirty) {
- return
- }
- m.read.Store(&readOnly{m: m.dirty})
- m.dirty = nil
- m.misses = 0
-}
-
-func (m *Map) dirtyLocked() {
- if m.dirty != nil {
- return
- }
-
- read := m.loadReadOnly()
- m.dirty = make(map[any]*entry, len(read.m))
- for k, e := range read.m {
- if !e.tryExpungeLocked() {
- m.dirty[k] = e
- }
- }
-}
-
-func (e *entry) tryExpungeLocked() (isExpunged bool) {
- p := e.p.Load()
- for p == nil {
- if e.p.CompareAndSwap(nil, expunged) {
- return true
- }
- p = e.p.Load()
- }
- return p == expunged
+ m.m.Range(f)
}