internal: add Release method for SelectResponse

The commit implements the SelectResponse.Release() method that frees
resources allocated for the response pointer to a sync.Pool.

Part of #493

Co-authored-by: Oleg Jukovec <oleg.jukovec@gmail.com>

Author: ermyar

request.go

@@ -620,14 +620,23 @@ func (req *SelectRequest) Context(ctx context.Context) *SelectRequest {
 	return req
 }
 
+var selectsPool *sync.Pool = &sync.Pool{
+	New: func() interface{} {
+		return &SelectResponse{}
+	},
+}
+
 // Response creates a response for the SelectRequest.
 func (req *SelectRequest) Response(header Header, body io.Reader) (Response, error) {
-	baseResp, err := createBaseResponse(header, body)
+	base, err := createBaseResponse(header, body)
 	if err != nil {
 		return nil, err
 	}
 
-	return &SelectResponse{baseResponse: baseResp}, nil
+	s := selectsPool.Get().(*SelectResponse)
+	s.baseResponse = base
+
+	return s, nil
 }
 
 // InsertRequest helps you to create an insert request object for execution

response.go

@@ -681,7 +681,10 @@ func (resp *baseResponse) Header() Header {
 
 func (resp *SelectResponse) Release() {
 	resp.baseResponse.Release()
-	resp.pos = nil
+
+	*resp = SelectResponse{}
+
+	selectsPool.Put(resp)
 }
 
 // Pos returns a position descriptor of the last selected tuple for the SelectResponse.

response_test.go

@@ -93,3 +93,64 @@ func TestSelectResponseRelease(t *testing.T) {
 	require.True(t, ok)
 	require.Equal(t, tarantool.SelectResponse{}, *selResp)
 }
+
+func TestSelectResponseReleaseReuse(t *testing.T) {
+	req := tarantool.NewSelectRequest(nil)
+
+	header1 := tarantool.Header{RequestId: 100}
+	buf1 := []byte{'d', 'a', 't', 'a', '1'}
+	resp1, err := req.Response(header1, encodeResponseData(t, buf1))
+	require.NoError(t, err)
+
+	data1, err := resp1.Decode()
+	require.NoError(t, err)
+	require.Equal(t, []interface{}{buf1}, data1)
+
+	resp1.Release()
+
+	header2 := tarantool.Header{RequestId: 200}
+	buf2 := []byte{'d', 'a', 't', 'a', '2'}
+	resp2, err := req.Response(header2, encodeResponseData(t, buf2))
+	require.NoError(t, err)
+
+	data2, err := resp2.Decode()
+	require.NoError(t, err)
+	require.Equal(t, []interface{}{buf2}, data2)
+	require.Equal(t, header2, resp2.Header())
+	require.Equal(t, []interface{}{buf2}, data2)
+}
+
+func TestSelectResponseReleaseMultipleObjects(t *testing.T) {
+	req := tarantool.NewSelectRequest(nil)
+
+	header1 := tarantool.Header{RequestId: 1}
+	buf1 := []byte{'o', 'n', 'e'}
+	resp1, err := req.Response(header1, encodeResponseData(t, buf1))
+	require.NoError(t, err)
+
+	header2 := tarantool.Header{RequestId: 2}
+	buf2 := []byte{'t', 'w', 'o'}
+	resp2, err := req.Response(header2, encodeResponseData(t, buf2))
+	require.NoError(t, err)
+
+	data1, err := resp1.Decode()
+	require.NoError(t, err)
+	require.Equal(t, []interface{}{buf1}, data1)
+
+	data2, err := resp2.Decode()
+	require.NoError(t, err)
+	require.Equal(t, []interface{}{buf2}, data2)
+
+	resp1.Release()
+	resp2.Release()
+
+	header3 := tarantool.Header{RequestId: 3}
+	buf3 := []byte{'t', 'h', 'r', 'e', 'e'}
+	resp3, err := req.Response(header3, encodeResponseData(t, buf3))
+	require.NoError(t, err)
+
+	data3, err := resp3.Decode()
+	require.NoError(t, err)
+	require.Equal(t, []interface{}{buf3}, data3)
+	require.Equal(t, header3, resp3.Header())
+}