github.com/nacos-group/nacos-sdk-go@v1.1.4/clients/cache/concurrent_map.go

/*

The MIT License (MIT)

Copyright (c) 2014 streamrail

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.

*/

package cache

import (
	"encoding/json"
	"sync"
)

var SHARD_COUNT = 32

// A "thread" safe map of type string:Anything.
// To avoid lock bottlenecks this map is dived to several (SHARD_COUNT) map shards.
type ConcurrentMap []*ConcurrentMapShared

// A "thread" safe string to anything map.
type ConcurrentMapShared struct {
	items        map[string]interface{}
	sync.RWMutex // Read Write mutex, guards access to internal map.
}

// Creates a new concurrent map.
func NewConcurrentMap() ConcurrentMap {
	m := make(ConcurrentMap, SHARD_COUNT)
	for i := 0; i < SHARD_COUNT; i++ {
		m[i] = &ConcurrentMapShared{items: make(map[string]interface{})}
	}
	return m
}

// Returns shard under given key
func (m ConcurrentMap) GetShard(key string) *ConcurrentMapShared {
	return m[uint(fnv32(key))%uint(SHARD_COUNT)]
}

func (m ConcurrentMap) MSet(data map[string]interface{}) {
	for key, value := range data {
		shard := m.GetShard(key)
		shard.Lock()
		shard.items[key] = value
		shard.Unlock()
	}
}

// Sets the given value under the specified key.
func (m ConcurrentMap) Set(key string, value interface{}) {
	// Get map shard.
	shard := m.GetShard(key)
	shard.Lock()
	shard.items[key] = value
	shard.Unlock()
}

// Callback to return new element to be inserted into the map
// It is called while lock is held, therefore it MUST NOT
// try to access other keys in same map, as it can lead to deadlock since
// Go sync.RWLock is not reentrant
type UpsertCb func(exist bool, valueInMap interface{}, newValue interface{}) interface{}

// Insert or Update - updates existing element or inserts a new one using UpsertCb
func (m ConcurrentMap) Upsert(key string, value interface{}, cb UpsertCb) (res interface{}) {
	shard := m.GetShard(key)
	shard.Lock()
	v, ok := shard.items[key]
	res = cb(ok, v, value)
	shard.items[key] = res
	shard.Unlock()
	return res
}

// Sets the given value under the specified key if no value was associated with it.
func (m ConcurrentMap) SetIfAbsent(key string, value interface{}) bool {
	// Get map shard.
	shard := m.GetShard(key)
	shard.Lock()
	_, ok := shard.items[key]
	if !ok {
		shard.items[key] = value
	}
	shard.Unlock()
	return !ok
}

// Retrieves an element from map under given key.
func (m ConcurrentMap) Get(key string) (interface{}, bool) {
	// Get shard
	shard := m.GetShard(key)
	shard.RLock()
	// Get item from shard.
	val, ok := shard.items[key]
	shard.RUnlock()
	return val, ok
}

// Returns the number of elements within the map.
func (m ConcurrentMap) Count() int {
	count := 0
	for i := 0; i < SHARD_COUNT; i++ {
		shard := m[i]
		shard.RLock()
		count += len(shard.items)
		shard.RUnlock()
	}
	return count
}

// Looks up an item under specified key
func (m ConcurrentMap) Has(key string) bool {
	// Get shard
	shard := m.GetShard(key)
	shard.RLock()
	// See if element is within shard.
	_, ok := shard.items[key]
	shard.RUnlock()
	return ok
}

// Removes an element from the map.
func (m ConcurrentMap) Remove(key string) {
	// Try to get shard.
	shard := m.GetShard(key)
	shard.Lock()
	delete(shard.items, key)
	shard.Unlock()
}

// Removes an element from the map and returns it
func (m ConcurrentMap) Pop(key string) (v interface{}, exists bool) {
	// Try to get shard.
	shard := m.GetShard(key)
	shard.Lock()
	v, exists = shard.items[key]
	delete(shard.items, key)
	shard.Unlock()
	return v, exists
}

// Checks if map is empty.
func (m ConcurrentMap) IsEmpty() bool {
	return m.Count() == 0
}

// Used by the Iter & IterBuffered functions to wrap two variables together over a channel,
type Tuple struct {
	Key string
	Val interface{}
}

// Returns an iterator which could be used in a for range loop.
//
// Deprecated: using IterBuffered() will get a better performence
func (m ConcurrentMap) Iter() <-chan Tuple {
	chans := snapshot(m)
	ch := make(chan Tuple)
	go fanIn(chans, ch)
	return ch
}

// Returns a buffered iterator which could be used in a for range loop.
func (m ConcurrentMap) IterBuffered() <-chan Tuple {
	chans := snapshot(m)
	total := 0
	for _, c := range chans {
		total += cap(c)
	}
	ch := make(chan Tuple, total)
	go fanIn(chans, ch)
	return ch
}

// Returns a array of channels that contains elements in each shard,
// which likely takes a snapshot of `m`.
// It returns once the size of each buffered channel is determined,
// before all the channels are populated using goroutines.
func snapshot(m ConcurrentMap) (chans []chan Tuple) {
	chans = make([]chan Tuple, SHARD_COUNT)
	wg := sync.WaitGroup{}
	wg.Add(SHARD_COUNT)
	// Foreach shard.
	for index, shard := range m {
		go func(index int, shard *ConcurrentMapShared) {
			// Foreach key, value pair.
			shard.RLock()
			chans[index] = make(chan Tuple, len(shard.items))
			wg.Done()
			for key, val := range shard.items {
				chans[index] <- Tuple{key, val}
			}
			shard.RUnlock()
			close(chans[index])
		}(index, shard)
	}
	wg.Wait()
	return chans
}

// fanIn reads elements from channels `chans` into channel `out`
func fanIn(chans []chan Tuple, out chan Tuple) {
	wg := sync.WaitGroup{}
	wg.Add(len(chans))
	for _, ch := range chans {
		go func(ch chan Tuple) {
			for t := range ch {
				out <- t
			}
			wg.Done()
		}(ch)
	}
	wg.Wait()
	close(out)
}

// Returns all items as map[string]interface{}
func (m ConcurrentMap) Items() map[string]interface{} {
	tmp := make(map[string]interface{})

	// Insert items to temporary map.
	for item := range m.IterBuffered() {
		tmp[item.Key] = item.Val
	}

	return tmp
}

// Iterator callback,called for every key,value found in
// maps. RLock is held for all calls for a given shard
// therefore callback sess consistent view of a shard,
// but not across the shards
type IterCb func(key string, v interface{})

// Callback based iterator, cheapest way to read
// all elements in a map.
func (m ConcurrentMap) IterCb(fn IterCb) {
	for idx := range m {
		shard := (m)[idx]
		shard.RLock()
		for key, value := range shard.items {
			fn(key, value)
		}
		shard.RUnlock()
	}
}

// Return all keys as []string
func (m ConcurrentMap) Keys() []string {
	count := m.Count()
	ch := make(chan string, count)
	go func() {
		// Foreach shard.
		wg := sync.WaitGroup{}
		wg.Add(SHARD_COUNT)
		for _, shard := range m {
			go func(shard *ConcurrentMapShared) {
				// Foreach key, value pair.
				shard.RLock()
				for key := range shard.items {
					ch <- key
				}
				shard.RUnlock()
				wg.Done()
			}(shard)
		}
		wg.Wait()
		close(ch)
	}()

	// Generate keys
	keys := make([]string, 0, count)
	for k := range ch {
		keys = append(keys, k)
	}
	return keys
}

//Reviles ConcurrentMap "private" variables to json marshal.
func (m ConcurrentMap) MarshalJSON() ([]byte, error) {
	// Create a temporary map, which will hold all item spread across shards.
	tmp := make(map[string]interface{})

	// Insert items to temporary map.
	for item := range m.IterBuffered() {
		tmp[item.Key] = item.Val
	}
	return json.Marshal(tmp)
}

func fnv32(key string) uint32 {
	hash := uint32(2166136261)
	const prime32 = uint32(16777619)
	for i := 0; i < len(key); i++ {
		hash *= prime32
		hash ^= uint32(key[i])
	}
	return hash
}

// Concurrent map uses Interface{} as its value, therefor JSON Unmarshal
// will probably won't know which to type to unmarshal into, in such case
// we'll end up with a value of type map[string]interface{}, In most cases this isn't
// out value type, this is why we've decided to remove this functionality.

// func (m *ConcurrentMap) UnmarshalJSON(b []byte) (err error) {
// 	// Reverse process of Marshal.

// 	tmp := make(map[string]interface{})

// 	// Unmarshal into a single map.
// 	if err := json.Unmarshal(b, &tmp); err != nil {
// 		return nil
// 	}

// 	// foreach key,value pair in temporary map insert into our concurrent map.
// 	for key, val := range tmp {
// 		m.Set(key, val)
// 	}
// 	return nil
// }