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|
package cmap
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.
// 分成SHARD_COUNT个分片的map
type ConcurrentMap []*ConcurrentMapShared
// A "thread" safe string to anything map.
// 通过RWMutex保护的线程安全的分片,包含一个map
type ConcurrentMapShared struct {
items map[string]interface{}
sync.RWMutex // Read Write mutex, guards access to internal map.
}
// Creates a new concurrent map.
// 创建并发map
func New() ConcurrentMap {
m := make(ConcurrentMap, SHARD_COUNT)
for i := 0; i < SHARD_COUNT; i++ {
m[i] = &ConcurrentMapShared{items: make(map[string]interface{})}
}
return m
}
// GetShard returns shard under given key
// 根据key计算分片索引
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.
//增加或者查询的时候,首先根据分片索引得到分片对象,然后对分片对象加锁进行操作:
func (m ConcurrentMap) Set(key string, value interface{}) {
// Get map shard.
// 根据key计算出对应的分片
shard := m.GetShard(key)
//对这个分片加锁,执行业务操作
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
}
// Get retrieves an element from map under given key.
func (m ConcurrentMap) Get(key string) (interface{}, bool) {
// Get shard
// 根据key计算出对应的分片
shard := m.GetShard(key)
shard.RLock()
// Get item from shard.
// 从这个分片读取key的值
val, ok := shard.items[key]
shard.RUnlock()
return val, ok
}
// Count 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
}
// Remove 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()
}
// RemoveCb is a callback executed in a map.RemoveCb() call, while Lock is held
// If returns true, the element will be removed from the map
type RemoveCb func(key string, v interface{}, exists bool) bool
// RemoveCb locks the shard containing the key, retrieves its current value and calls the callback with those params
// If callback returns true and element exists, it will remove it from the map
// Returns the value returned by the callback (even if element was not present in the map)
func (m ConcurrentMap) RemoveCb(key string, cb RemoveCb) bool {
// Try to get shard.
shard := m.GetShard(key)
shard.Lock()
v, ok := shard.items[key]
remove := cb(key, v, ok)
if remove && ok {
delete(shard.items, key)
}
shard.Unlock()
return remove
}
// Pop 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
}
// IsEmpty 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{}
}
// Iter 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
}
// IterBuffered 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
}
// Clear removes all items from map.
func (m ConcurrentMap) Clear() {
for item := range m.IterBuffered() {
m.Remove(item.Key)
}
}
// 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)
}
// Items 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()
}
}
// Keys returns 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
// }
|