/
cache.go
330 lines (274 loc) · 8.34 KB
/
cache.go
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package main
import (
"encoding/binary"
"encoding/json"
"fmt"
"io/ioutil"
"os"
"path/filepath"
"sync"
"time"
)
type ReadRequest struct {
key string
receiver chan interface{}
}
type WriteRequest struct {
key string
value interface{}
}
type PeekRequest struct {
key string
receiver chan bool
}
type CacheUpdateFunc func(string) (interface{}, error)
type CacheSession struct {
Updater CacheUpdateFunc
Retries int
CacheOnError bool
db map[string]interface{}
waitingClients map[string][]chan interface{} // some requesters are waiting for db entry.
workers sync.WaitGroup
peekChan chan PeekRequest
readChan chan ReadRequest
writeChan chan WriteRequest
jobQueue chan ReadRequest
}
func NewCacheSession(updater CacheUpdateFunc, retries int, cacheOnError bool, nworkers int) *CacheSession {
s := CacheSession{
Updater: updater,
Retries: retries,
CacheOnError: cacheOnError,
db: make(map[string]interface{}),
waitingClients: make(map[string][]chan interface{}),
readChan: make(chan ReadRequest),
peekChan: make(chan PeekRequest),
jobQueue: make(chan ReadRequest),
writeChan: make(chan WriteRequest),
}
for i := 0; i < nworkers; i++ {
go s.cacheSessionWorker(i)
}
go s.server()
return &s
}
func (s *CacheSession) Close() {
Debug.Printf("CacheSession.Close(): closing READ channel")
close(s.readChan)
close(s.peekChan)
}
func (s *CacheSession) finalize() {
Debug.Printf("CacheSession.finalize(): closing JOB QUEUE channel")
close(s.jobQueue)
Debug.Printf("CacheSession.finalize(): readChan CLOSED!")
done := make(chan struct{})
go func() {
s.workers.Wait()
close(done)
}()
for {
select {
case <-done:
close(s.writeChan)
return
case <-s.writeChan:
// do nothing
}
}
}
func (s *CacheSession) server() {
defer Debug.Printf("CacheSession.server(): end")
Debug.Printf("CacheSession.server(): start")
serial := 0
for {
select {
case req := <-s.peekChan:
// Debug.Printf("CacheSession.server[%d]: PEEK: Request(key = %s) received", serial, req.key)
if req == (PeekRequest{}) {
break
}
_, ok := s.db[req.key]
go func(in chan bool, val bool) {
in <- val
}(req.receiver, ok)
case req := <-s.readChan:
// Debug.Printf("CacheSession.server[%d]: READ: Request(key = %s) received", serial, req.key)
if req == (ReadRequest{}) {
s.finalize()
return
}
img, ok := s.db[req.key]
if ok {
if req.receiver != nil {
// Debug.Printf("CacheSession.server[%d]: READ: craete goroutine for returning value for key = %s", serial, req.key)
go func(in chan interface{}, img interface{}) {
defer close(in)
in <- img
}(req.receiver, img)
}
} else { // s.db[req.key] is not ready.
// Debug.Printf("CacheSession.server[%d]: READ: no entry in the DB for key = %s", serial, req.key)
if _, ok := s.waitingClients[req.key]; ok {
if req.receiver != nil {
s.waitingClients[req.key] = append(s.waitingClients[req.key], req.receiver)
// Debug.Printf("CacheSession.server[%d]: READ: added Request(key = %s) to the waiting list (%d waiters)", serial, req.key, len(s.waitingClients[req.key]))
// Debug.Printf("CacheSession.server[%d]: READ: waiting list: %v", serial, s.waitingClients[req.key])
} else {
// Debug.Printf("CacheSession.server[%d]: READ: Request(key = %s) has no receiver", serial, req.key)
}
} else {
// Debug.Printf("CacheSession.server[%d]: READ: none in waiting list, send Request(key = %s) to job queue", serial, req.key)
s.waitingClients[req.key] = append(s.waitingClients[req.key], req.receiver)
go func(r ReadRequest) {
s.jobQueue <- r
}(req)
}
}
// Debug.Printf("CacheSession.server[%d]: READ: done Request(key = %s)", serial, req.key)
case req := <-s.writeChan:
if req == (WriteRequest{}) {
break
}
// Debug.Printf("CacheSession.server[%d]: WRITE: Request(key = %s) received", serial, req.key)
if _, ok := req.value.(error); ok {
if s.CacheOnError {
s.db[req.key] = req.value
}
} else {
s.db[req.key] = req.value
}
for _, waitCh := range s.waitingClients[req.key] {
func(ch chan interface{}, value interface{}) {
if ch != nil {
defer close(ch)
ch <- value
}
}(waitCh, req.value)
// Debug.Printf("CacheSession.server[%d]: WRITE: broadcasted value of DB[%s] to all waiters", serial, req.key)
}
// Debug.Printf("CacheSession.server[%d]: WRITE: done Request(key = %s)", serial, req.key)
}
serial++
}
}
func (s *CacheSession) cacheSessionWorker(workerId int) {
s.workers.Add(1)
defer s.workers.Done()
serial := 0
for req := range s.jobQueue {
// Debug.Printf("CacheSession.worker[%d:%d]: retrieved Request(key = %s)", workerId, serial, req.key)
// Debug.Printf("CacheSession.worker[%d:%d]: calling Updater(key = %s)", workerId, serial, req.key)
var value interface{}
var err error
for i := 0; i < s.Retries+1; i++ {
value, err = s.Updater(req.key)
if err == nil {
break
}
Debug.Printf("CacheSession.worker[%d:%d]: Updater(key = %s) failed for %d times, err = %s", workerId, serial, req.key, i+1, err)
}
// s.writeChan <- WriteRequest{key: req.key, value: &img}
if err == nil {
/*
go func(ch chan WriteRequest, req WriteRequest) {
ch <- req
}(s.writeChan, WriteRequest{key: req.key, value: value})
*/
// Debug.Printf("CacheSession.worker[%d:%d]: Updater(%s) success; sending WriteRequest() to the server", workerId, serial, req.key)
s.writeChan <- WriteRequest{key: req.key, value: value}
} else {
Debug.Printf("CacheSession.worker[%d:%d]: Updater(%s) failure; err = %s", workerId, serial, req.key, err)
Debug.Printf("CacheSession.worker[%d:%d]: Caching err for key = %s", workerId, serial, err)
s.writeChan <- WriteRequest{key: req.key, value: err}
}
/*
if req.receiver != nil {
if err == nil {
Debug.Printf("CacheSession.worker[%d:%d]: sending the value for ReadRequest(%s) to the requester", workerId, serial, req.key)
go func(in chan interface{}, v interface{}) {
defer close(in)
in <- v
}(req.receiver, value)
} else {
Debug.Printf("CacheSession.worker[%d:%d]: sending an error for ReadRequest(%s) to the requester", workerId, serial, req.key)
go func(in chan interface{}, v interface{}) {
defer close(in)
in <- v
}(req.receiver, err)
}
}
*/
serial++
}
}
func (s *CacheSession) Prepare(key string) {
// defer func() { Debug.Printf("Prepare() done") }()
go func() { s.readChan <- ReadRequest{key: key} }()
}
func (s *CacheSession) Get(key string) (interface{}, error) {
// defer func() { Debug.Printf("Get() done") }()
ch := make(chan interface{})
s.readChan <- ReadRequest{key: key, receiver: ch}
value := <-ch
if err, ok := value.(error); ok {
return nil, err
}
return value, nil
}
func (s *CacheSession) Peek(key string) bool {
// defer func() { Debug.Printf("Peek() done") }()
ch := make(chan bool)
s.peekChan <- PeekRequest{key: key, receiver: ch}
return <-ch
}
func ReadDataFromFileCache(fileName string, expiration time.Duration) ([]byte, error) {
stat, err := os.Stat(fileName)
if err != nil {
return nil, err
}
if stat.ModTime().Add(expiration).Before(time.Now()) {
return nil, fmt.Errorf("cache expired")
}
b, err := ioutil.ReadFile(fileName)
if err != nil {
remove_err := os.Remove(fileName)
if remove_err != nil {
return nil, fmt.Errorf("cannot read %s (%s), nor can delete it (%s)", err, remove_err)
}
return nil, fmt.Errorf("cannot read %s (%s), removed")
}
return b, nil
}
func WriteDataToFileCache(fileName string, data []byte) error {
os.MkdirAll(filepath.Dir(fileName), 0755)
f, err := os.Create(fileName)
if err != nil {
return err
}
defer f.Close()
err = binary.Write(f, binary.LittleEndian, data)
if err != nil {
return err
}
return nil
}
func ReadJsonFromFileCache(fileName string, expiration time.Duration, v interface{}) error {
b, err := ReadDataFromFileCache(fileName, expiration)
if err != nil {
return err
}
err = json.Unmarshal(b, v)
if err != nil {
os.Remove(fileName)
return err
}
return nil
}
func WriteJsonToFileCache(fileName string, v interface{}) error {
// func WriteDataToFileCache(fileName string, data []byte) error {
b, err := json.Marshal(v)
if err != nil {
return err
}
return WriteDataToFileCache(fileName, b)
}