func (s *supportContext) mkRandKeys(keys []ds.Key, metas ds.MultiMetaGetter) []string {
ret := []string(nil)
for i, key := range keys {
if !metas.GetMetaDefault(i, CacheEnableMeta, true).(bool) {
continue
}
shards := s.numShards(key)
if shards == 0 {
continue
}
if ret == nil {
ret = make([]string, len(keys))
}
ret[i] = MakeMemcacheKey(s.mr.Intn(shards), key)
}
return ret
}
func (d *dsCache) GetMulti(keys []ds.Key, metas ds.MultiMetaGetter, cb ds.GetMultiCB) error {
lockItems, nonce := d.mkRandLockItems(keys, metas)
if len(lockItems) == 0 {
return d.RawInterface.GetMulti(keys, metas, cb)
}
if err := d.mc.AddMulti(lockItems); err != nil {
(log.Fields{log.ErrorKey: err}).Warningf(
d.c, "dscache: GetMulti: memcache.AddMulti")
}
if err := d.mc.GetMulti(lockItems); err != nil {
(log.Fields{log.ErrorKey: err}).Warningf(
d.c, "dscache: GetMulti: memcache.GetMulti")
}
p := makeFetchPlan(d.c, d.aid, d.ns, &facts{keys, metas, lockItems, nonce})
if !p.empty() {
// looks like we have something to pull from datastore, and maybe some work
// to save stuff back to memcache.
toCas := []memcache.Item{}
j := 0
err := d.RawInterface.GetMulti(p.toGet, p.toGetMeta, func(pm ds.PropertyMap, err error) {
i := p.idxMap[j]
toSave := p.toSave[j]
j++
data := []byte(nil)
// true: save entity to memcache
// false: lock entity in memcache forever
shouldSave := true
if err == nil {
p.decoded[i] = pm
if toSave != nil {
data = encodeItemValue(pm)
if len(data) > internalValueSizeLimit {
shouldSave = false
log.Warningf(
d.c, "dscache: encoded entity too big (%d/%d)!",
len(data), internalValueSizeLimit)
}
}
} else {
p.lme.Assign(i, err)
if err != ds.ErrNoSuchEntity {
return // aka continue to the next entry
}
}
if toSave != nil {
if shouldSave { // save
expSecs := metas.GetMetaDefault(i, CacheExpirationMeta, CacheTimeSeconds).(int64)
toSave.SetFlags(uint32(ItemHasData))
toSave.SetExpiration(time.Duration(expSecs) * time.Second)
toSave.SetValue(data)
} else {
// Set a lock with an infinite timeout. No one else should try to
// serialize this item to memcache until something Put/Delete's it.
toSave.SetFlags(uint32(ItemHasLock))
toSave.SetExpiration(0)
toSave.SetValue(nil)
}
toCas = append(toCas, toSave)
}
})
if err != nil {
return err
}
if len(toCas) > 0 {
// we have entries to save back to memcache.
if err := d.mc.CompareAndSwapMulti(toCas); err != nil {
(log.Fields{log.ErrorKey: err}).Warningf(
d.c, "dscache: GetMulti: memcache.CompareAndSwapMulti")
}
}
}
// finally, run the callback for all of the decoded items and the errors,
// if any.
for i, dec := range p.decoded {
cb(dec, p.lme.GetOne(i))
}
return nil
}
