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syncAtomic.go
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syncAtomic.go
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package congomap
import (
"sync"
"sync/atomic"
"time"
)
type syncAtomicMap struct {
db atomic.Value
duration time.Duration
halt chan struct{}
lock sync.Mutex // used only by writers
lookup func(string) (interface{}, error)
reaper func(interface{})
ttl bool
// TODO: some way to do this with atomics?
loading map[string]*sync.WaitGroup
loading_lock sync.Mutex
}
// NewSyncAtomicMap returns a map that uses sync/atomic.Value to serialize
// access.
func NewSyncAtomicMap(setters ...Setter) (Congomap, error) {
cgm := &syncAtomicMap{
halt: make(chan struct{}),
loading: make(map[string]*sync.WaitGroup),
}
cgm.db.Store(make(map[string]expiringValue))
for _, setter := range setters {
if err := setter(cgm); err != nil {
return nil, err
}
}
if cgm.lookup == nil {
cgm.lookup = func(_ string) (interface{}, error) {
return nil, ErrNoLookupDefined{}
}
}
go cgm.run()
return cgm, nil
}
// Lookup sets the lookup callback function for this Congomap for use
// when `LoadStore` is called and a requested key is not in the map.
func (cgm *syncAtomicMap) Lookup(lookup func(string) (interface{}, error)) error {
cgm.lookup = lookup
return nil
}
// Reaper is used to specify what function is to be called when
// garbage collecting item from the Congomap.
func (cgm *syncAtomicMap) Reaper(reaper func(interface{})) error {
cgm.reaper = reaper
return nil
}
// TTL sets the time-to-live for values stored in the Congomap.
func (cgm *syncAtomicMap) TTL(duration time.Duration) error {
if duration <= 0 {
return ErrInvalidDuration(duration)
}
cgm.duration = duration
cgm.ttl = true
return nil
}
// Delete removes a key value pair from a Congomap.
func (cgm *syncAtomicMap) Delete(key string) {
cgm.lock.Lock() // synchronize with other potential writers
m := cgm.copyNonExpiredData(nil)
if cgm.reaper != nil {
if ev, ok := m[key]; ok {
cgm.reaper(ev.value)
}
}
delete(m, key) // remove the specified item
cgm.db.Store(m) // atomically replace the current object with the new one
// At this point all new readers start working with the new version.
// The old version will be garbage collected once the existing readers
// (if any) are done with it.
cgm.lock.Unlock()
}
// GC forces elimination of keys in Congomap with values that have
// expired.
func (cgm *syncAtomicMap) GC() {
if cgm.ttl {
cgm.lock.Lock()
m := cgm.copyNonExpiredData(nil)
cgm.db.Store(m) // atomically replace the current object with the new one
cgm.lock.Unlock()
}
}
// Load gets the value associated with the given key. When the key is
// in the map, it returns the value associated with the key and
// true. Otherwise it returns nil for the value and false.
func (cgm *syncAtomicMap) Load(key string) (interface{}, bool) {
ev, ok := cgm.db.Load().(map[string]expiringValue)[key]
if ok && (!cgm.ttl || ev.expiry > time.Now().UnixNano()) {
return ev.value, true
}
return nil, false
}
// Store sets the value associated with the given key.
func (cgm *syncAtomicMap) Store(key string, value interface{}) {
cgm.lock.Lock() // synchronize with other potential writers
m := cgm.copyNonExpiredData(nil)
ev := expiringValue{value: value}
if cgm.ttl {
ev.expiry = time.Now().UnixNano() + int64(cgm.duration)
}
m[key] = ev // do the update that we need
cgm.db.Store(m) // atomically replace the current object with the new one
// At this point all new readers start working with the new version.
// The old version will be garbage collected once the existing readers
// (if any) are done with it.
cgm.lock.Unlock()
}
// LoadStore gets the value associated with the given key if it's in
// the map. If it's not in the map, it calls the lookup function, and
// sets the value in the map to that returned by the lookup function.
func (cgm *syncAtomicMap) LoadStore(key string) (interface{}, error) {
cgm.lock.Lock() // synchronize with other potential writers
m1 := cgm.db.Load().(map[string]expiringValue) // load current value of the data structure
// load
ev, ok := m1[key]
if ok && (!cgm.ttl || ev.expiry > time.Now().UnixNano()) {
return ev.value, nil
}
cgm.lock.Unlock() // Unlock whole map, since we are just loading
// Lock the loading map
cgm.loading_lock.Lock()
wg, ok := cgm.loading[key]
// If someone else is already loading, lets just wait on them
if ok {
cgm.loading_lock.Unlock()
wg.Wait()
return cgm.LoadStore(key) // TODO: don't recurse?
} else {
// No one else is loading
// Lets create a wait group, and unlock the loading map
var wg sync.WaitGroup
wg.Add(1)
cgm.loading[key] = &wg
cgm.loading_lock.Unlock()
// Do the actual load
// key was expired or not in db
value, err := cgm.lookup(key)
if err != nil {
return nil, err
}
ev = expiringValue{value: value}
if cgm.ttl {
ev.expiry = time.Now().UnixNano() + int64(cgm.duration)
}
// We have the value, lets set it and remove the loading entry
cgm.lock.Lock()
// Refetch the current one, since it might have changed while we didn't have the lock
m1 = cgm.db.Load().(map[string]expiringValue) // load current value of the data structure
m2 := cgm.copyNonExpiredData(m1)
ev = expiringValue{value: value}
if cgm.ttl {
ev.expiry = time.Now().UnixNano() + int64(cgm.duration)
}
m2[key] = ev // do the update that we need
cgm.db.Store(m2) // atomically replace the current object with the new one
cgm.lock.Unlock()
// Remove our entry of loading
cgm.loading_lock.Lock()
delete(cgm.loading, key)
cgm.loading_lock.Unlock()
// mark the thing as loaded
wg.Done()
return value, nil
}
}
// Keys returns an array of key values stored in the map.
func (cgm *syncAtomicMap) Keys() []string {
var keys []string
m1 := cgm.db.Load().(map[string]expiringValue) // load current value of the data structure
for k := range m1 {
keys = append(keys, k)
}
return keys
}
// Pairs returns a channel through which key value pairs are
// read. Pairs will lock the Congomap so that no other accessors can
// be used until the returned channel is closed.
func (cgm *syncAtomicMap) Pairs() <-chan *Pair {
cgm.lock.Lock()
pairs := make(chan *Pair)
go func(pairs chan<- *Pair) {
m1 := cgm.db.Load().(map[string]expiringValue) // load current value of the data structure
now := time.Now().UnixNano()
for k, v := range m1 {
if !cgm.ttl || (v.expiry > now) {
pairs <- &Pair{k, v.value}
}
}
close(pairs)
cgm.lock.Unlock()
}(pairs)
return pairs
}
// Close releases resources used by the Congomap.
func (cgm *syncAtomicMap) Close() error {
cgm.halt <- struct{}{}
return nil
}
// Halt releases resources used by the Congomap.
func (cgm *syncAtomicMap) Halt() {
cgm.halt <- struct{}{}
}
func (cgm *syncAtomicMap) run() {
duration := 5 * cgm.duration
if !cgm.ttl {
duration = time.Hour
} else if duration < time.Second {
duration = time.Minute
}
active := true
for active {
select {
case <-time.After(duration):
cgm.GC()
case <-cgm.halt:
active = false
}
}
if cgm.reaper != nil {
m1 := cgm.db.Load().(map[string]expiringValue) // load current value of the data structure
for _, ev := range m1 {
cgm.reaper(ev.value)
}
}
}
func (cgm *syncAtomicMap) copyNonExpiredData(m1 map[string]expiringValue) map[string]expiringValue {
var now int64
if cgm.ttl {
now = time.Now().UnixNano()
}
if m1 == nil {
m1 = cgm.db.Load().(map[string]expiringValue) // load current value of the data structure
}
m2 := make(map[string]expiringValue) // create a new value
for k, v := range m1 {
if !cgm.ttl || v.expiry > now {
m2[k] = v // copy non-expired data from the current object to the new one
} else if cgm.reaper != nil {
cgm.reaper(v.value)
}
}
return m2
}