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@@ -1,371 +0,0 @@
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-// Copyright 2016 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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-
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-//go:build !go1.9
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-// +build !go1.9
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-
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-package syncmap
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-
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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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-
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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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-
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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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-
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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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-
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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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-
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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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-
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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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-
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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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-
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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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-
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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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-
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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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-
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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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-
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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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-
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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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-
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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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-
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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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-
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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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-
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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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-
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- return actual, loaded
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-}
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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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-
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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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-
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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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-
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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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-
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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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-
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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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-
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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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-
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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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-
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- read, _ := m.read.Load().(readOnly)
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- m.dirty = make(map[interface{}]*entry, len(read.m))
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- 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
|
|
|
|
-}
|
|
|