implement init parameters selection with etcd

go/glide.lock

 hash: 1b9b07408ca7fac27a374dc2ccd2433e4bff090484008a037df967284949a582
-updated: 2017-08-03T21:46:51.744995189Z
+updated: 2017-08-07T23:37:48.867469328Z
 imports:
 - name: github.com/beorn7/perks
   version: 4c0e84591b9aa9e6dcfdf3e020114cd81f89d5f9
@@ -10,7 +10,7 @@ imports:
 - name: github.com/cockroachdb/cmux
   version: 112f0506e7743d64a6eb8fedbcff13d9979bbf92
 - name: github.com/coreos/etcd
-  version: c31bec0f29facff13f7c3e3d948e55dd6689ed42
+  version: d0d1a87aa96ae14914751d42264262cb69eda170
   subpackages:
   - alarm
   - auth
@@ -24,6 +24,7 @@ imports:
   - error
   - etcdserver
   - etcdserver/api
+  - etcdserver/api/etcdhttp
   - etcdserver/api/v2http
   - etcdserver/api/v2http/httptypes
   - etcdserver/api/v3client
@@ -210,11 +211,6 @@ testImports:
   version: 04cdfd42973bb9c8589fd6a731800cf222fde1a9
   subpackages:
   - spew
-- name: github.com/docker/docker
-  version: b6d164e6c46d8115b146e4c3ac93784e9ef8b49e
-  subpackages:
-  - pkg/ioutils
-  - pkg/longpath
 - name: github.com/pmezard/go-difflib
   version: d8ed2627bdf02c080bf22230dbb337003b7aba2d
   subpackages:

go/master/service_test.go

 package master_test
 
 import (
+	"io/ioutil"
 	"os"
 	"testing"
 	"time"
@@ -8,13 +9,12 @@ import (
 	"github.com/PaddlePaddle/Paddle/go/master"
 	"github.com/coreos/etcd/clientv3"
 	"github.com/coreos/etcd/embed"
-	"github.com/docker/docker/pkg/ioutils"
 	"github.com/stretchr/testify/assert"
 )
 
 func TestNewServiceWithEtcd(t *testing.T) {
 	// setup an embed etcd server
-	etcdDir, err := ioutils.TempDir("", "")
+	etcdDir, err := ioutil.TempDir("", "")
 	if err != nil {
 		t.Fatal(err)
 	}

go/pserver/client/c/cclient.go

@@ -90,8 +90,12 @@ func cArrayToSlice(p unsafe.Pointer, len int) []byte {
 
 type selector bool
 
-func (s selector) Select() bool {
-	return bool(s)
+func (s selector) Select() (bool, error) {
+	return bool(s), nil
+}
+
+func (s selector) Done() error {
+	return nil
 }
 
 type lister []client.Server
@@ -114,11 +118,10 @@ func paddle_new_pserver_client(addrs *C.char, selected int) C.paddle_pserver_cli
 }
 
 //export paddle_new_etcd_pserver_client
-func paddle_new_etcd_pserver_client(etcdEndpoints *C.char, selected int) C.paddle_pserver_client {
-	// TODO(Longfei: use etcd lock to decide which trainer to initialize the parameters)
+func paddle_new_etcd_pserver_client(etcdEndpoints *C.char) C.paddle_pserver_client {
 	addr := C.GoString(etcdEndpoints)
 	etcdClient := client.NewEtcd(addr)
-	c := client.NewClient(etcdClient, etcdClient.Desired(), selector(selected != 0))
+	c := client.NewClient(etcdClient, etcdClient.Desired(), etcdClient)
 	return add(c)
 }
 
@@ -136,7 +139,12 @@ func paddle_pserver_client_release(client C.paddle_pserver_client) {
 //export paddle_begin_init_params
 func paddle_begin_init_params(client C.paddle_pserver_client) C.int {
 	c := get(client)
-	if selected := c.BeginInitParams(); selected {
+	selected, err := c.BeginInitParams()
+	if err != nil {
+		panic(err)
+	}
+
+	if selected {
 		return 1
 	}
 	return 0

go/pserver/client/client.go

@@ -27,9 +27,13 @@ import (
 
 // TODO(helin): add RPC call retry logic
 
-// Selector selects if the client should initialize parameter servers.
+// Selector selects if the client should initialize parameters and
+// reports the initialization process done.
 type Selector interface {
-	Select() bool
+	// Select selects if the client should initialize parameter servers.
+	Select() (bool, error)
+	// Done indicates the initialization process is done.
+	Done() error
 }
 
 // Server is the identification of a parameter Server.
@@ -115,7 +119,7 @@ func (c *Client) monitorPservers(l Lister, pserverNum int) {
 // servers. Other trainers will be blocked until the initialization is
 // done, and they need to get the initialized parameters from
 // parameter servers using GetParams.
-func (c *Client) BeginInitParams() bool {
+func (c *Client) BeginInitParams() (bool, error) {
 	return c.sel.Select()
 }
 

go/pserver/client/client_test.go

@@ -124,8 +124,12 @@ func initEtcdClient() {
 
 type selector bool
 
-func (s selector) Select() bool {
-	return bool(s)
+func (s selector) Select() (bool, error) {
+	return bool(s), nil
+}
+
+func (s selector) Done() error {
+	return nil
 }
 
 type lister []client.Server
@@ -135,7 +139,11 @@ func (l lister) List() []client.Server {
 }
 
 func testClient(t *testing.T, c *client.Client) {
-	selected := c.BeginInitParams()
+	selected, err := c.BeginInitParams()
+	if err != nil {
+		t.Fatal(err)
+	}
+
 	if !selected {
 		t.Fatal("should be selected.")
 	}

go/pserver/client/etcd_client.go

@@ -16,53 +16,60 @@ package client
 
 import (
 	"context"
+	"errors"
+	"fmt"
 	"strconv"
 	"strings"
 	"time"
 
 	"github.com/PaddlePaddle/Paddle/go/pserver"
 	"github.com/coreos/etcd/clientv3"
+	"github.com/coreos/etcd/clientv3/concurrency"
 	log "github.com/sirupsen/logrus"
 )
 
 const (
 	defaultEtcdTimeout time.Duration = 5 * time.Second
+
+	initLockPath = "/init_ps/lock"
+	initDonePath = "/init_ps/done"
+	initDoneVal  = "1"
 )
 
-// EtcdClient is used by pserver client that is a part of trainer process.
+// Etcd is used by pserver client that is a part of trainer process.
 // TODO:
-// 1. add watcher to watch the change state of pservers)
-// 1. add etcd lock)
-type EtcdClient struct {
+// 1. add watcher to watch the change state of pservers.
+type Etcd struct {
 	client    *clientv3.Client
 	timeout   time.Duration
 	endpoints []string
+	lock      *concurrency.Mutex
 }
 
 // Desired read ps desired number from etcd.
-func (p *EtcdClient) Desired() int {
+func (e *Etcd) Desired() int {
 	var psDesired int
 	for {
-		ctx, cancel := context.WithTimeout(context.Background(), p.timeout)
-		resp, err := p.client.Get(ctx, pserver.PsDesired)
+		ctx, cancel := context.WithTimeout(context.Background(), e.timeout)
+		resp, err := e.client.Get(ctx, pserver.PsDesired)
 		cancel()
 		if err != nil {
 			log.Errorf("Get ps dresire number failed! recnnectiong..., %v", err)
-			time.Sleep(p.timeout)
+			time.Sleep(e.timeout)
 			continue
 		}
 
 		kvs := resp.Kvs
 		if len(kvs) == 0 {
 			log.Infoln("Waiting for ps desired registered ...")
-			time.Sleep(p.timeout)
+			time.Sleep(e.timeout)
 			continue
 		}
 
 		psDesired, err = strconv.Atoi(string(resp.Kvs[0].Value))
 		if err != nil {
 			log.Errorf("psDesired %d invalid %v", psDesired, err)
-			time.Sleep(p.timeout)
+			time.Sleep(e.timeout)
 			continue
 		}
 
@@ -73,26 +80,26 @@ func (p *EtcdClient) Desired() int {
 }
 
 // List return the pserver list read from etcd.
-func (p *EtcdClient) List() []Server {
-	psDesired := p.Desired()
+func (e *Etcd) List() []Server {
+	psDesired := e.Desired()
 
 	servers := make([]Server, psDesired)
 	for {
 		for i := 0; i < psDesired; i++ {
-			ctx, cancel := context.WithTimeout(context.Background(), p.timeout)
+			ctx, cancel := context.WithTimeout(context.Background(), e.timeout)
 			psKey := pserver.PsPath + strconv.Itoa(i)
 			log.Debugf("checking %s", psKey)
-			resp, err := p.client.Get(ctx, psKey)
+			resp, err := e.client.Get(ctx, psKey)
 			cancel()
 			if err != nil {
 				log.Infof("Get psKey= %s error, %v", psKey, err)
-				time.Sleep(p.timeout)
+				time.Sleep(e.timeout)
 				continue
 			}
 			kvs := resp.Kvs
 			if len(kvs) == 0 {
 				log.Infof("Waiting for ps addr registered ...")
-				time.Sleep(p.timeout)
+				time.Sleep(e.timeout)
 				continue
 			}
 
@@ -100,7 +107,7 @@ func (p *EtcdClient) List() []Server {
 			// TODO(Longfei) check the ps address
 			if psAddr == "" {
 				log.Infof("Get psKey = %s, psAddr is empty", psKey)
-				time.Sleep(p.timeout)
+				time.Sleep(e.timeout)
 				continue
 			}
 			log.Debugf("got value (%s) for key: %s", psAddr, psKey)
@@ -113,7 +120,7 @@ func (p *EtcdClient) List() []Server {
 }
 
 // NewEtcd create a etcd client to return the state of pserver on etcd.
-func NewEtcd(endpoints string) *EtcdClient {
+func NewEtcd(endpoints string) *Etcd {
 	ep := strings.Split(endpoints, ",")
 	var cli *clientv3.Client
 	var err error
@@ -130,10 +137,118 @@ func NewEtcd(endpoints string) *EtcdClient {
 		break
 	}
 	log.Infof("Connected to etcd: %s\n", endpoints)
-	client := &EtcdClient{
+	client := &Etcd{
 		client:    cli,
 		timeout:   defaultEtcdTimeout,
 		endpoints: ep,
 	}
 	return client
 }
+
+// Select indicates if the current trainer is selected to initialize
+// the pserver parameters.
+func (e *Etcd) Select() (bool, error) {
+	sess, err := concurrency.NewSession(e.client, concurrency.WithTTL(5))
+	if err != nil {
+		return false, err
+	}
+
+	lock := concurrency.NewMutex(sess, initLockPath)
+	log.Infof("Trying to acquire lock at %s.", initLockPath)
+	// Do not use timeout context here, since we don't know how
+	// long does it take for other trainers to initialize the
+	// parameters.
+	err = lock.Lock(context.Background())
+	if err != nil {
+		return false, err
+	}
+	log.Infof("Successfully acquired lock at %s.", initLockPath)
+
+	get := clientv3.OpGet(initDonePath)
+	ctx, cancel := context.WithTimeout(context.Background(), e.timeout)
+	tresp, err := e.client.Txn(ctx).If(lock.IsOwner()).Then(get).Commit()
+	cancel()
+	if err != nil {
+		return false, err
+	}
+
+	if !tresp.Succeeded {
+		return false, errors.New("no longer the owner of the lock")
+	}
+
+	resp := tresp.Responses[0].GetResponseRange()
+
+	if len(resp.Kvs) == 0 {
+		// Key value not set, select current trainer.
+		e.lock = lock
+		log.Infoln("Trainer selected.")
+		return true, nil
+	}
+
+	if string(resp.Kvs[0].Value) == initDoneVal {
+		log.Infoln("Initialization is already done.")
+		ctx, cancel = context.WithTimeout(context.Background(), e.timeout)
+		err = lock.Unlock(ctx)
+		cancel()
+		if err != nil {
+			log.Errorln(err)
+		}
+		return false, nil
+	}
+
+	return false, fmt.Errorf("key %s have unexpected value: %v", initDonePath, resp.Kvs[0].Value)
+}
+
+// Done indicates the parameter initialization process is done.
+func (e *Etcd) Done() error {
+	if e.lock == nil {
+		return errors.New("lock is nil, Done called unexpectedly")
+	}
+
+	put := clientv3.OpPut(initDonePath, initDoneVal)
+	ctx, cancel := context.WithTimeout(context.Background(), e.timeout)
+	tresp, err := e.client.Txn(ctx).If(e.lock.IsOwner()).Then(put).Commit()
+	cancel()
+	if err != nil {
+		return err
+	}
+
+	if !tresp.Succeeded {
+		return errors.New("no longer the owner of the lock")
+	}
+
+	ctx, cancel = context.WithTimeout(context.Background(), e.timeout)
+	err = e.lock.Unlock(ctx)
+	cancel()
+	if err != nil {
+		log.Errorln(err)
+	} else {
+		e.lock = nil
+	}
+
+	return nil
+}
+
+// Close closes the etcd client.
+func (e *Etcd) Close() error {
+	var err error
+	if e.lock != nil {
+		ctx, cancel := context.WithTimeout(context.Background(), e.timeout)
+		err = e.lock.Unlock(ctx)
+		cancel()
+		if err == nil {
+			e.lock = nil
+		}
+	}
+
+	cErr := e.client.Close()
+	if cErr != nil {
+		if err != nil {
+			log.Errorln(cErr)
+			return err
+		}
+		return cErr
+	}
+
+	return err
+}

go/pserver/client/etcd_client_test.go

+package client_test
+
+import (
+	"io/ioutil"
+	"os"
+	"sync"
+	"testing"
+
+	"github.com/PaddlePaddle/Paddle/go/pserver/client"
+	"github.com/coreos/etcd/embed"
+)
+
+func TestSelector(t *testing.T) {
+	etcdDir, err := ioutil.TempDir("", "")
+	if err != nil {
+		t.Fatal(err)
+	}
+	cfg := embed.NewConfig()
+	cfg.Dir = etcdDir
+	e, err := embed.StartEtcd(cfg)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	defer func() {
+		e.Close()
+		if err := os.RemoveAll(etcdDir); err != nil {
+			t.Fatal(err)
+		}
+	}()
+
+	<-e.Server.ReadyNotify()
+
+	var mu sync.Mutex
+	selectedCount := 0
+	var wg sync.WaitGroup
+	selectAndDone := func(c *client.Etcd) {
+		defer wg.Done()
+
+		selected, err := c.Select()
+		if err != nil {
+			panic(err)
+		}
+
+		if selected {
+			mu.Lock()
+			selectedCount++
+			mu.Unlock()
+			err = c.Done()
+			if err != nil {
+				t.Fatal(err)
+			}
+		}
+	}
+
+	c0 := client.NewEtcd("127.0.0.1:2379")
+	c1 := client.NewEtcd("127.0.0.1:2379")
+	c2 := client.NewEtcd("127.0.0.1:2379")
+	c3 := client.NewEtcd("127.0.0.1:2379")
+	wg.Add(3)
+	go selectAndDone(c0)
+	go selectAndDone(c1)
+	go selectAndDone(c2)
+	wg.Wait()
+
+	// simulate trainer crashed and restarted after the
+	// initialization process.
+	wg.Add(1)
+	go selectAndDone(c3)
+	wg.Wait()
+
+	mu.Lock()
+	if selectedCount != 1 {
+		t.Fatal("selected count wrong:", selectedCount)
+	}
+	mu.Unlock()
+
+	err = c0.Close()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	err = c1.Close()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	err = c2.Close()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	err = c3.Close()
+	if err != nil {
+		t.Fatal(err)
+	}
+}

paddle/trainer/NewRemoteParameterUpdater.cpp

@@ -51,7 +51,7 @@ void NewRemoteParameterUpdater::init(
   // create parameter server client.
   if (useEtcd_) {
     parameterClient_ = paddle_new_etcd_pserver_client(
-        (char *)pserverSpec_.c_str(), FLAGS_trainer_id == 0);
+        (char *)pserverSpec_.c_str());
   } else {
     parameterClient_ = paddle_new_pserver_client((char *)pserverSpec_.c_str(),
                                                  FLAGS_trainer_id == 0);