"saving checkpoint"

go/pserver/service.go

 package pserver
 
 import (
+	"bufio"
+	"bytes"
+	"crypto/md5"
+	"encoding/gob"
+	"encoding/hex"
 	"errors"
 	"fmt"
+	"os"
+	"strconv"
 	"sync"
+	"time"
+
+	log "github.com/sirupsen/logrus"
 )
 
 // ElementType is the type of elements of a Parameter.
@@ -14,6 +24,10 @@ const (
 	Uninitialized      = "pserver not fully initialized"
 )
 
+const (
+	checkpoint_path = "/checkpoints/"
+)
+
 // Supported element types
 const (
 	Int32 ElementType = iota
@@ -53,6 +67,24 @@ type Service struct {
 	optMap map[string]*optimizer
 }
 
+type Checkpoint struct {
+	uuid      string
+	md5sum    string
+	timestamp string
+}
+
+//serialize ParameterWithConfig to byte stream
+func GetBytes(content ...interface{}) ([]byte, error) {
+
+	var buf bytes.Buffer
+	encoder := gob.NewEncoder(&buf)
+	err := encoder.Encode(content)
+	if err != nil {
+		return nil, err
+	}
+	return buf.Bytes(), nil
+}
+
 // NewService creates a new service, will bypass etcd registration if no
 // endpoints specified.
 func NewService(idx int) (*Service, error) {
@@ -143,13 +175,50 @@ func (s *Service) GetParam(name string, parameter *Parameter) error {
 
 // Save tells the parameter server to save parameters.
 func (s *Service) Save(path string, dummy *int) error {
+	//FIXME: checkpoint is only used by pserver
+	// and has a constant path of */checkpoints/{pserver_idx}*
 	<-s.initialized
-	for opt, ok := range s.optMap {
-		if ok != nil {
-			return fmt.Errorf("parameter optimizerMap error: ", ok)
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	var paramWithConfig ParameterWithConfig
+	for name, opt := range s.optMap {
+		paramWithConfig.Param.Name = name
+		paramWithConfig.Param.ElementType = opt.elementType
+		paramWithConfig.Param.Content = opt.GetWeights()
+		paramWithConfig.State = opt.GetStates()
+		content, err := GetBytes(paramWithConfig)
+		if err != nil {
+			log.Errorln(err)
+		}
+		ck := Checkpoint{}
+		h := md5.New()
+		ck.md5sum = hex.EncodeToString(h.Sum(content))
+		ck.timestamp = time.Now().String()
+		ck.uuid = checkpoint_path + strconv.Itoa(s.idx)
+		ckbytes, err := GetBytes(ck)
+		if err != nil {
+			log.Errorln(err)
+		}
+		// TODO: according design doc, need to save uuid to etcd in json format
+		// {\"uuid\": [UUID], \"md5\", \"MD5 sum\", \"timestamp\": xxxx}
+		log.Infof("parameter checkpoint %s", ckbytes)
+
+		if _, err = os.Stat(ck.uuid); os.IsNotExist(err) {
+			log.Info("checkpoint not exists.")
+		} else {
+			err = os.Remove(ck.uuid)
+			log.Infof("remove %s", ck.uuid)
+		}
+		f, err := os.Create(ck.uuid)
+		defer f.Close()
+		if err != nil {
+			log.Errorln(err)
+		}
+		writer := bufio.NewWriter(f)
+		_, err = writer.Write(content)
+		if err != nil {
+			log.Errorln(err)
 		}
-		state := opt.GetStates()
-		weights := opt.GetWeights()
 	}
 	return nil
 }

go/pserver/service_test.go

@@ -79,6 +79,8 @@ func TestServiceFull(t *testing.T) {
 	if !reflect.DeepEqual(param1, p) {
 		t.FailNow()
 	}
+	var dummy int
+	s.Save("", &dummy)
 }
 
 func TestMultipleInit(t *testing.T) {
@@ -166,3 +168,7 @@ func TestBlockUntilInitialized(t *testing.T) {
 
 	wg.Wait()
 }
+
+func TestCheckpointSpeed(t *testing.T) {
+	//TODO: test speed
+}