详解Go语言如何实现并发安全的map

type RWMap struct {
    sync.RWMutex
    m map[any]any
}

func NewGRWMap() *RWMap {
    return &RWMap{
       m: make(map[any]any),
    }
}
func (m *RWMap) Get(k int) (any, bool) {
    m.RLock()
    defer m.RUnlock()
    v, existed := m.m[k]
    return v, existed
}

func (m *RWMap) Set(k any, v any) {
    m.Lock()
    defer m.Unlock()
    m.m[k] = v
}

func (m *RWMap) Delete(k any) {
    m.Lock()
    defer m.Unlock()
    delete(m.m, k)
}

func (m *RWMap) Len() int {
    m.RLock()
    defer m.RUnlock()
    return len(m.m)
}

func (m *RWMap) Each(f func(k, v any) bool) {
    m.RLock()
    defer m.RUnlock()

    for k, v := range m.m {
       if !f(k, v) {
          return
       }
    }
}

var SHARD_COUNT = 32

type ConcurrentMap[K comparable, V any] struct {
	shards   []*ConcurrentMapShared[K, V]
	sharding func(key K) uint32
}

type ConcurrentMapShared[K comparable, V any] struct {
	items        map[K]V
	sync.RWMutex 
}

func create[K comparable, V any](sharding func(key K) uint32) ConcurrentMap[K, V] {
	m := ConcurrentMap[K, V]{
		sharding: sharding,
		shards:   make([]*ConcurrentMapShared[K, V], SHARD_COUNT),
	}
	for i := 0; i < SHARD_COUNT; i++ {
		m.shards[i] = &ConcurrentMapShared[K, V]{items: make(map[K]V)}
	}
	return m
}

func New[V any]() ConcurrentMap[string, V] {
	return create[string, V](fnv32)
}


func NewWithCustomShardingFunction[K comparable, V any](sharding func(key K) uint32) ConcurrentMap[K, V] {
    return create[K, V](sharding)
}

func (m ConcurrentMap[K, V]) Set(key K, value V) {
    shard := m.GetShard(key)
    shard.Lock()
    shard.items[key] = value
    shard.Unlock()
}

func (m ConcurrentMap[K, V]) GetShard(key K) *ConcurrentMapShared[K, V] {
	return m.shards[uint(m.sharding(key))%uint(SHARD_COUNT)]
}

type Map struct {
	mu Mutex
	read atomic.Pointer[readOnly]
	dirty map[any]*entry
	misses int
}


type readOnly struct {
	m       map[any]*entry
	amended bool
}


type entry struct {
	p atomic.Pointer[any]
}

func (x *Pointer[T]) Load() *T { return (*T)(LoadPointer(&x.v)) }

func (m *Map) loadReadOnly() readOnly {
    if p := m.read.Load(); p != nil {
       return *p
    }
    return readOnly{}
}

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()

       read = m.loadReadOnly()
       e, ok = read.m[key]
       if !ok && read.amended {
          e, ok = m.dirty[key]
          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
}

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) Store(key, value any) {
    _, _ = m.Swap(key, value)
}

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
}


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 (m *Map) Delete(key any) {
    m.LoadAndDelete(key)
}

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)
			m.missLocked()
		}
		m.mu.Unlock()
	}
	if ok {
		return e.delete()
	}
	return nil, false
}

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
		}
	}
}

func (m *Map) Range(f func(key, value any) bool) {
    read := m.loadReadOnly()
    if read.amended {
       m.mu.Lock()
       read = m.loadReadOnly()
       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
       }
    }
}