syncmap: use type alias for Map
sync.Map was introduced in Go 1.9, this change updates the syncmap package to use a type alias to sync.Map for 1.9 and later. It also updates the comments to reflect this change. Fixes golang/go#33867 Change-Id: Ia58ad2bc409f8fcb8a7539ef165148315da5cfb1 Reviewed-on: https://go-review.googlesource.com/c/sync/+/192737 Reviewed-by: Bryan C. Mills <bcmills@google.com> Run-TryBot: Bryan C. Mills <bcmills@google.com> TryBot-Result: Gobot Gobot <gobot@golang.org>
This commit is contained in:
Eric Rutherford
Bryan C. Mills
parent
112230192c
commit
cd5d95a43a
3 changed files with 390 additions and 367 deletions
17
syncmap/go19.go
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17
syncmap/go19.go
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@ -0,0 +1,17 @@
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// Copyright 2019 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// +build go1.9
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package syncmap
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import "sync" // home to the standard library's sync.map implementation as of Go 1.9
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// Map is a concurrent map with amortized-constant-time loads, stores, and deletes.
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// It is safe for multiple goroutines to call a Map's methods concurrently.
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//
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// The zero Map is valid and empty.
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//
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// A Map must not be copied after first use.
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type Map = sync.Map
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370
syncmap/map.go
370
syncmap/map.go
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@ -1,372 +1,8 @@
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// Copyright 2016 The Go Authors. All rights reserved.
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// Copyright 2019 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// license that can be found in the LICENSE file.
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// Package syncmap provides a concurrent map implementation.
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// Package syncmap provides a concurrent map implementation.
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// It is a prototype for a proposed addition to the sync package
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// This was the prototype for sync.Map which was added to the standard library's
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// in the standard library.
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// sync package in Go 1.9. https://golang.org/pkg/sync/#Map.
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// (https://golang.org/issue/18177)
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package syncmap
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package syncmap
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import (
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"sync"
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"sync/atomic"
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"unsafe"
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)
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// Map is a concurrent map with amortized-constant-time loads, stores, and deletes.
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// It is safe for multiple goroutines to call a Map's methods concurrently.
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//
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// The zero Map is valid and empty.
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//
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// A Map must not be copied after first use.
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type Map struct {
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mu sync.Mutex
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// read contains the portion of the map's contents that are safe for
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// concurrent access (with or without mu held).
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//
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// The read field itself is always safe to load, but must only be stored with
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// mu held.
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//
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// Entries stored in read may be updated concurrently without mu, but updating
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// a previously-expunged entry requires that the entry be copied to the dirty
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// map and unexpunged with mu held.
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read atomic.Value // readOnly
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// dirty contains the portion of the map's contents that require mu to be
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// held. To ensure that the dirty map can be promoted to the read map quickly,
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// it also includes all of the non-expunged entries in the read map.
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//
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// Expunged entries are not stored in the dirty map. An expunged entry in the
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// clean map must be unexpunged and added to the dirty map before a new value
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// can be stored to it.
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//
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// If the dirty map is nil, the next write to the map will initialize it by
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// making a shallow copy of the clean map, omitting stale entries.
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dirty map[interface{}]*entry
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// misses counts the number of loads since the read map was last updated that
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// needed to lock mu to determine whether the key was present.
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//
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// Once enough misses have occurred to cover the cost of copying the dirty
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// map, the dirty map will be promoted to the read map (in the unamended
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// state) and the next store to the map will make a new dirty copy.
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misses int
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}
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// readOnly is an immutable struct stored atomically in the Map.read field.
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type readOnly struct {
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m map[interface{}]*entry
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amended bool // true if the dirty map contains some key not in m.
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}
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// expunged is an arbitrary pointer that marks entries which have been deleted
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// from the dirty map.
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var expunged = unsafe.Pointer(new(interface{}))
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// An entry is a slot in the map corresponding to a particular key.
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type entry struct {
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// p points to the interface{} value stored for the entry.
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//
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// If p == nil, the entry has been deleted and m.dirty == nil.
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//
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// If p == expunged, the entry has been deleted, m.dirty != nil, and the entry
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// is missing from m.dirty.
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//
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// Otherwise, the entry is valid and recorded in m.read.m[key] and, if m.dirty
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// != nil, in m.dirty[key].
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//
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// An entry can be deleted by atomic replacement with nil: when m.dirty is
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// next created, it will atomically replace nil with expunged and leave
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// m.dirty[key] unset.
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//
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// An entry's associated value can be updated by atomic replacement, provided
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// p != expunged. If p == expunged, an entry's associated value can be updated
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// only after first setting m.dirty[key] = e so that lookups using the dirty
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// map find the entry.
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p unsafe.Pointer // *interface{}
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}
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func newEntry(i interface{}) *entry {
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return &entry{p: unsafe.Pointer(&i)}
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}
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// Load returns the value stored in the map for a key, or nil if no
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// value is present.
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// The ok result indicates whether value was found in the map.
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func (m *Map) Load(key interface{}) (value interface{}, ok bool) {
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read, _ := m.read.Load().(readOnly)
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e, ok := read.m[key]
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if !ok && read.amended {
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m.mu.Lock()
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// Avoid reporting a spurious miss if m.dirty got promoted while we were
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// blocked on m.mu. (If further loads of the same key will not miss, it's
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// not worth copying the dirty map for this key.)
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read, _ = m.read.Load().(readOnly)
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e, ok = read.m[key]
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if !ok && read.amended {
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e, ok = m.dirty[key]
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// Regardless of whether the entry was present, record a miss: this key
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// will take the slow path until the dirty map is promoted to the read
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// map.
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m.missLocked()
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}
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m.mu.Unlock()
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}
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if !ok {
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return nil, false
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}
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return e.load()
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}
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func (e *entry) load() (value interface{}, ok bool) {
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p := atomic.LoadPointer(&e.p)
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if p == nil || p == expunged {
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return nil, false
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}
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return *(*interface{})(p), true
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}
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// Store sets the value for a key.
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func (m *Map) Store(key, value interface{}) {
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read, _ := m.read.Load().(readOnly)
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if e, ok := read.m[key]; ok && e.tryStore(&value) {
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return
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}
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m.mu.Lock()
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read, _ = m.read.Load().(readOnly)
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if e, ok := read.m[key]; ok {
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if e.unexpungeLocked() {
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// The entry was previously expunged, which implies that there is a
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// non-nil dirty map and this entry is not in it.
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m.dirty[key] = e
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}
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e.storeLocked(&value)
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} else if e, ok := m.dirty[key]; ok {
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e.storeLocked(&value)
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} else {
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if !read.amended {
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// We're adding the first new key to the dirty map.
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// Make sure it is allocated and mark the read-only map as incomplete.
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m.dirtyLocked()
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m.read.Store(readOnly{m: read.m, amended: true})
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}
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m.dirty[key] = newEntry(value)
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}
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m.mu.Unlock()
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}
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// tryStore stores a value if the entry has not been expunged.
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//
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// If the entry is expunged, tryStore returns false and leaves the entry
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// unchanged.
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func (e *entry) tryStore(i *interface{}) bool {
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p := atomic.LoadPointer(&e.p)
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if p == expunged {
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return false
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}
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for {
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if atomic.CompareAndSwapPointer(&e.p, p, unsafe.Pointer(i)) {
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return true
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}
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p = atomic.LoadPointer(&e.p)
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if p == expunged {
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return false
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}
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}
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}
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// unexpungeLocked ensures that the entry is not marked as expunged.
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//
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// If the entry was previously expunged, it must be added to the dirty map
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// before m.mu is unlocked.
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func (e *entry) unexpungeLocked() (wasExpunged bool) {
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return atomic.CompareAndSwapPointer(&e.p, expunged, nil)
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}
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// storeLocked unconditionally stores a value to the entry.
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//
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// The entry must be known not to be expunged.
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func (e *entry) storeLocked(i *interface{}) {
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atomic.StorePointer(&e.p, unsafe.Pointer(i))
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}
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// LoadOrStore returns the existing value for the key if present.
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// Otherwise, it stores and returns the given value.
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// The loaded result is true if the value was loaded, false if stored.
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func (m *Map) LoadOrStore(key, value interface{}) (actual interface{}, loaded bool) {
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// Avoid locking if it's a clean hit.
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read, _ := m.read.Load().(readOnly)
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if e, ok := read.m[key]; ok {
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actual, loaded, ok := e.tryLoadOrStore(value)
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if ok {
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return actual, loaded
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}
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}
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m.mu.Lock()
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read, _ = m.read.Load().(readOnly)
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if e, ok := read.m[key]; ok {
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if e.unexpungeLocked() {
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m.dirty[key] = e
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}
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actual, loaded, _ = e.tryLoadOrStore(value)
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} else if e, ok := m.dirty[key]; ok {
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actual, loaded, _ = e.tryLoadOrStore(value)
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m.missLocked()
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} else {
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if !read.amended {
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// We're adding the first new key to the dirty map.
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// Make sure it is allocated and mark the read-only map as incomplete.
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m.dirtyLocked()
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m.read.Store(readOnly{m: read.m, amended: true})
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}
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m.dirty[key] = newEntry(value)
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actual, loaded = value, false
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}
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m.mu.Unlock()
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return actual, loaded
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}
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// tryLoadOrStore atomically loads or stores a value if the entry is not
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// expunged.
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//
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// If the entry is expunged, tryLoadOrStore leaves the entry unchanged and
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// returns with ok==false.
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func (e *entry) tryLoadOrStore(i interface{}) (actual interface{}, loaded, ok bool) {
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p := atomic.LoadPointer(&e.p)
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if p == expunged {
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return nil, false, false
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}
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if p != nil {
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return *(*interface{})(p), true, true
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}
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// Copy the interface after the first load to make this method more amenable
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// to escape analysis: if we hit the "load" path or the entry is expunged, we
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// shouldn't bother heap-allocating.
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ic := i
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for {
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if atomic.CompareAndSwapPointer(&e.p, nil, unsafe.Pointer(&ic)) {
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return i, false, true
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}
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p = atomic.LoadPointer(&e.p)
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if p == expunged {
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return nil, false, false
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}
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if p != nil {
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return *(*interface{})(p), true, true
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}
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}
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}
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// Delete deletes the value for a key.
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func (m *Map) Delete(key interface{}) {
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read, _ := m.read.Load().(readOnly)
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e, ok := read.m[key]
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if !ok && read.amended {
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m.mu.Lock()
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read, _ = m.read.Load().(readOnly)
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e, ok = read.m[key]
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if !ok && read.amended {
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delete(m.dirty, key)
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}
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m.mu.Unlock()
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}
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if ok {
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e.delete()
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}
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}
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func (e *entry) delete() (hadValue bool) {
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for {
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p := atomic.LoadPointer(&e.p)
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if p == nil || p == expunged {
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return false
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}
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if atomic.CompareAndSwapPointer(&e.p, p, nil) {
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return true
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}
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}
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}
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// Range calls f sequentially for each key and value present in the map.
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// If f returns false, range stops the iteration.
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//
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// Range does not necessarily correspond to any consistent snapshot of the Map's
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// contents: no key will be visited more than once, but if the value for any key
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// is stored or deleted concurrently, Range may reflect any mapping for that key
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// from any point during the Range call.
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//
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// Range may be O(N) with the number of elements in the map even if f returns
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// false after a constant number of calls.
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func (m *Map) Range(f func(key, value interface{}) bool) {
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// We need to be able to iterate over all of the keys that were already
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// present at the start of the call to Range.
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// If read.amended is false, then read.m satisfies that property without
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// requiring us to hold m.mu for a long time.
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read, _ := m.read.Load().(readOnly)
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if read.amended {
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// m.dirty contains keys not in read.m. Fortunately, Range is already O(N)
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// (assuming the caller does not break out early), so a call to Range
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// amortizes an entire copy of the map: we can promote the dirty copy
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// immediately!
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m.mu.Lock()
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read, _ = m.read.Load().(readOnly)
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if read.amended {
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read = readOnly{m: m.dirty}
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m.read.Store(read)
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m.dirty = nil
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m.misses = 0
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}
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m.mu.Unlock()
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}
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for k, e := range read.m {
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v, ok := e.load()
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if !ok {
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continue
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}
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if !f(k, v) {
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break
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}
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}
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}
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func (m *Map) missLocked() {
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m.misses++
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if m.misses < len(m.dirty) {
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return
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}
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m.read.Store(readOnly{m: m.dirty})
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m.dirty = nil
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m.misses = 0
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}
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func (m *Map) dirtyLocked() {
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if m.dirty != nil {
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return
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}
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read, _ := m.read.Load().(readOnly)
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|
||||||
m.dirty = make(map[interface{}]*entry, len(read.m))
|
|
||||||
for k, e := range read.m {
|
|
||||||
if !e.tryExpungeLocked() {
|
|
||||||
m.dirty[k] = e
|
|
||||||
}
|
|
||||||
}
|
|
||||||
}
|
|
||||||
|
|
||||||
func (e *entry) tryExpungeLocked() (isExpunged bool) {
|
|
||||||
p := atomic.LoadPointer(&e.p)
|
|
||||||
for p == nil {
|
|
||||||
if atomic.CompareAndSwapPointer(&e.p, nil, expunged) {
|
|
||||||
return true
|
|
||||||
}
|
|
||||||
p = atomic.LoadPointer(&e.p)
|
|
||||||
}
|
|
||||||
return p == expunged
|
|
||||||
}
|
|
||||||
|
|
|
||||||
370
syncmap/pre_go19.go
Normal file
370
syncmap/pre_go19.go
Normal file
|
|
@ -0,0 +1,370 @@
|
||||||
|
// Copyright 2016 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.
|
||||||
|
|
||||||
|
// +build !go1.9
|
||||||
|
|
||||||
|
package syncmap
|
||||||
|
|
||||||
|
import (
|
||||||
|
"sync"
|
||||||
|
"sync/atomic"
|
||||||
|
"unsafe"
|
||||||
|
)
|
||||||
|
|
||||||
|
// Map is a concurrent map with amortized-constant-time loads, stores, and deletes.
|
||||||
|
// It is safe for multiple goroutines to call a Map's methods concurrently.
|
||||||
|
//
|
||||||
|
// The zero Map is valid and empty.
|
||||||
|
//
|
||||||
|
// A Map must not be copied after first use.
|
||||||
|
type Map struct {
|
||||||
|
mu sync.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.Value // 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[interface{}]*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[interface{}]*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 = unsafe.Pointer(new(interface{}))
|
||||||
|
|
||||||
|
// 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 m.dirty == nil.
|
||||||
|
//
|
||||||
|
// 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 unsafe.Pointer // *interface{}
|
||||||
|
}
|
||||||
|
|
||||||
|
func newEntry(i interface{}) *entry {
|
||||||
|
return &entry{p: unsafe.Pointer(&i)}
|
||||||
|
}
|
||||||
|
|
||||||
|
// 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 interface{}) (value interface{}, ok bool) {
|
||||||
|
read, _ := m.read.Load().(readOnly)
|
||||||
|
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.read.Load().(readOnly)
|
||||||
|
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 interface{}, ok bool) {
|
||||||
|
p := atomic.LoadPointer(&e.p)
|
||||||
|
if p == nil || p == expunged {
|
||||||
|
return nil, false
|
||||||
|
}
|
||||||
|
return *(*interface{})(p), true
|
||||||
|
}
|
||||||
|
|
||||||
|
// Store sets the value for a key.
|
||||||
|
func (m *Map) Store(key, value interface{}) {
|
||||||
|
read, _ := m.read.Load().(readOnly)
|
||||||
|
if e, ok := read.m[key]; ok && e.tryStore(&value) {
|
||||||
|
return
|
||||||
|
}
|
||||||
|
|
||||||
|
m.mu.Lock()
|
||||||
|
read, _ = m.read.Load().(readOnly)
|
||||||
|
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
|
||||||
|
}
|
||||||
|
e.storeLocked(&value)
|
||||||
|
} else if e, ok := m.dirty[key]; ok {
|
||||||
|
e.storeLocked(&value)
|
||||||
|
} 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()
|
||||||
|
}
|
||||||
|
|
||||||
|
// tryStore stores a value if the entry has not been expunged.
|
||||||
|
//
|
||||||
|
// If the entry is expunged, tryStore returns false and leaves the entry
|
||||||
|
// unchanged.
|
||||||
|
func (e *entry) tryStore(i *interface{}) bool {
|
||||||
|
p := atomic.LoadPointer(&e.p)
|
||||||
|
if p == expunged {
|
||||||
|
return false
|
||||||
|
}
|
||||||
|
for {
|
||||||
|
if atomic.CompareAndSwapPointer(&e.p, p, unsafe.Pointer(i)) {
|
||||||
|
return true
|
||||||
|
}
|
||||||
|
p = atomic.LoadPointer(&e.p)
|
||||||
|
if p == expunged {
|
||||||
|
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 atomic.CompareAndSwapPointer(&e.p, expunged, nil)
|
||||||
|
}
|
||||||
|
|
||||||
|
// storeLocked unconditionally stores a value to the entry.
|
||||||
|
//
|
||||||
|
// The entry must be known not to be expunged.
|
||||||
|
func (e *entry) storeLocked(i *interface{}) {
|
||||||
|
atomic.StorePointer(&e.p, unsafe.Pointer(i))
|
||||||
|
}
|
||||||
|
|
||||||
|
// 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 interface{}) (actual interface{}, loaded bool) {
|
||||||
|
// Avoid locking if it's a clean hit.
|
||||||
|
read, _ := m.read.Load().(readOnly)
|
||||||
|
if e, ok := read.m[key]; ok {
|
||||||
|
actual, loaded, ok := e.tryLoadOrStore(value)
|
||||||
|
if ok {
|
||||||
|
return actual, loaded
|
||||||
|
}
|
||||||
|
}
|
||||||
|
|
||||||
|
m.mu.Lock()
|
||||||
|
read, _ = m.read.Load().(readOnly)
|
||||||
|
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 interface{}) (actual interface{}, loaded, ok bool) {
|
||||||
|
p := atomic.LoadPointer(&e.p)
|
||||||
|
if p == expunged {
|
||||||
|
return nil, false, false
|
||||||
|
}
|
||||||
|
if p != nil {
|
||||||
|
return *(*interface{})(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 atomic.CompareAndSwapPointer(&e.p, nil, unsafe.Pointer(&ic)) {
|
||||||
|
return i, false, true
|
||||||
|
}
|
||||||
|
p = atomic.LoadPointer(&e.p)
|
||||||
|
if p == expunged {
|
||||||
|
return nil, false, false
|
||||||
|
}
|
||||||
|
if p != nil {
|
||||||
|
return *(*interface{})(p), true, true
|
||||||
|
}
|
||||||
|
}
|
||||||
|
}
|
||||||
|
|
||||||
|
// Delete deletes the value for a key.
|
||||||
|
func (m *Map) Delete(key interface{}) {
|
||||||
|
read, _ := m.read.Load().(readOnly)
|
||||||
|
e, ok := read.m[key]
|
||||||
|
if !ok && read.amended {
|
||||||
|
m.mu.Lock()
|
||||||
|
read, _ = m.read.Load().(readOnly)
|
||||||
|
e, ok = read.m[key]
|
||||||
|
if !ok && read.amended {
|
||||||
|
delete(m.dirty, key)
|
||||||
|
}
|
||||||
|
m.mu.Unlock()
|
||||||
|
}
|
||||||
|
if ok {
|
||||||
|
e.delete()
|
||||||
|
}
|
||||||
|
}
|
||||||
|
|
||||||
|
func (e *entry) delete() (hadValue bool) {
|
||||||
|
for {
|
||||||
|
p := atomic.LoadPointer(&e.p)
|
||||||
|
if p == nil || p == expunged {
|
||||||
|
return false
|
||||||
|
}
|
||||||
|
if atomic.CompareAndSwapPointer(&e.p, p, nil) {
|
||||||
|
return true
|
||||||
|
}
|
||||||
|
}
|
||||||
|
}
|
||||||
|
|
||||||
|
// 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.
|
||||||
|
//
|
||||||
|
// 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 interface{}) 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.read.Load().(readOnly)
|
||||||
|
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.read.Load().(readOnly)
|
||||||
|
if read.amended {
|
||||||
|
read = readOnly{m: m.dirty}
|
||||||
|
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.read.Load().(readOnly)
|
||||||
|
m.dirty = make(map[interface{}]*entry, len(read.m))
|
||||||
|
for k, e := range read.m {
|
||||||
|
if !e.tryExpungeLocked() {
|
||||||
|
m.dirty[k] = e
|
||||||
|
}
|
||||||
|
}
|
||||||
|
}
|
||||||
|
|
||||||
|
func (e *entry) tryExpungeLocked() (isExpunged bool) {
|
||||||
|
p := atomic.LoadPointer(&e.p)
|
||||||
|
for p == nil {
|
||||||
|
if atomic.CompareAndSwapPointer(&e.p, nil, expunged) {
|
||||||
|
return true
|
||||||
|
}
|
||||||
|
p = atomic.LoadPointer(&e.p)
|
||||||
|
}
|
||||||
|
return p == expunged
|
||||||
|
}
|
||||||
Loading…
Add table
Add a link
Reference in a new issue