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Diffstat (limited to 'vendor/golang.org/x/sync/syncmap/map.go')
| -rw-r--r-- | vendor/golang.org/x/sync/syncmap/map.go | 372 |
1 files changed, 0 insertions, 372 deletions
diff --git a/vendor/golang.org/x/sync/syncmap/map.go b/vendor/golang.org/x/sync/syncmap/map.go deleted file mode 100644 index 80e15847ef..0000000000 --- a/vendor/golang.org/x/sync/syncmap/map.go +++ /dev/null @@ -1,372 +0,0 @@ -// 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. - -// Package syncmap provides a concurrent map implementation. -// It is a prototype for a proposed addition to the sync package -// in the standard library. -// (https://golang.org/issue/18177) -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 -} |