align memcache operations with redis

@@ -21,7 +21,11 @@ func NewMemCache() *MemcacheCache {
 // get value from memcache.
 func (rc *MemcacheCache) Get(key string) interface{} {
 	if rc.c == nil {
-		rc.c = rc.connectInit()
+		var err error
+		rc.c, err = rc.connectInit()
+		if err != nil {
+			return err
+		}
 	}
 	v, err := rc.c.Get(key)
 	if err != nil {
@@ -39,7 +43,11 @@ func (rc *MemcacheCache) Get(key string) interface{} {
 // put value to memcache. only support string.
 func (rc *MemcacheCache) Put(key string, val interface{}, timeout int64) error {
 	if rc.c == nil {
-		rc.c = rc.connectInit()
+		var err error
+		rc.c, err = rc.connectInit()
+		if err != nil {
+			return err
+		}
 	}
 	v, ok := val.(string)
 	if !ok {
@@ -55,7 +63,11 @@ func (rc *MemcacheCache) Put(key string, val interface{}, timeout int64) error {
 // delete value in memcache.
 func (rc *MemcacheCache) Delete(key string) error {
 	if rc.c == nil {
-		rc.c = rc.connectInit()
+		var err error
+		rc.c, err = rc.connectInit()
+		if err != nil {
+			return err
+		}
 	}
 	_, err := rc.c.Delete(key)
 	return err
@@ -76,7 +88,11 @@ func (rc *MemcacheCache) Decr(key string) error {
 // check value exists in memcache.
 func (rc *MemcacheCache) IsExist(key string) bool {
 	if rc.c == nil {
-		rc.c = rc.connectInit()
+		var err error
+		rc.c, err = rc.connectInit()
+		if err != nil {
+			return false
+		}
 	}
 	v, err := rc.c.Get(key)
 	if err != nil {
@@ -93,7 +109,11 @@ func (rc *MemcacheCache) IsExist(key string) bool {
 // clear all cached in memcache.
 func (rc *MemcacheCache) ClearAll() error {
 	if rc.c == nil {
-		rc.c = rc.connectInit()
+		var err error
+		rc.c, err = rc.connectInit()
+		if err != nil {
+			return err
+		}
 	}
 	err := rc.c.FlushAll()
 	return err
@@ -109,20 +129,21 @@ func (rc *MemcacheCache) StartAndGC(config string) error {
 		return errors.New("config has no conn key")
 	}
 	rc.conninfo = cf["conn"]
-	rc.c = rc.connectInit()
-	if rc.c == nil {
+	var err error
+	rc.c, err = rc.connectInit()
+	if err != nil {
 		return errors.New("dial tcp conn error")
 	}
 	return nil
 }
 
 // connect to memcache and keep the connection.
-func (rc *MemcacheCache) connectInit() *memcache.Connection {
+func (rc *MemcacheCache) connectInit() (*memcache.Connection, error) {
 	c, err := memcache.Connect(rc.conninfo)
 	if err != nil {
-		return nil
+		return nil, err
 	}
-	return c
+	return c, nil
 }
 
 func init() {