sessionctx: fix hidden and user var problems in encoding session states

session/session.go

@@ -4151,8 +4151,9 @@ func (s *session) EncodeSessionStates(ctx context.Context, sctx sessionctx.Conte
 	sessionStates.SystemVars = make(map[string]string)
 	for _, sv := range variable.GetSysVars() {
 		switch {
-		case sv.Hidden, sv.HasNoneScope(), sv.HasInstanceScope(), !sv.HasSessionScope():
-			// Hidden and none-scoped variables cannot be modified.
+		case sv.HasNoneScope(), sv.HasInstanceScope(), !sv.HasSessionScope():
+			// Hidden attribute is deprecated.
+			// None-scoped variables cannot be modified.
 			// Instance-scoped variables don't need to be encoded.
 			// Noop variables should also be migrated even if they are noop.
 			continue

sessionctx/sessionstates/session_states_test.go

@@ -107,8 +107,9 @@ func TestSystemVars(t *testing.T) {
 		},
 		{
 			// hidden variable
-			inSessionStates: false,
+			inSessionStates: true,
 			varName:         variable.TiDBTxnReadTS,
+			expectedValue:   "",
 		},
 		{
 			// none-scoped variable

sessionctx/variable/BUILD.bazel

@@ -95,10 +95,12 @@ go_test(
         "//parser/mysql",
         "//parser/terror",
         "//planner/core",
+        "//sessionctx/sessionstates",
         "//sessionctx/stmtctx",
         "//testkit",
         "//testkit/testsetup",
         "//types",
+        "//util",
         "//util/chunk",
         "//util/execdetails",
         "//util/gctuner",

sessionctx/variable/session.go

@@ -2291,16 +2291,16 @@ func (s *SessionVars) GetTemporaryTable(tblInfo *model.TableInfo) tableutil.Temp
 // EncodeSessionStates saves session states into SessionStates.
 func (s *SessionVars) EncodeSessionStates(ctx context.Context, sessionStates *sessionstates.SessionStates) (err error) {
 	// Encode user-defined variables.
+	s.userVars.lock.RLock()
 	sessionStates.UserVars = make(map[string]*types.Datum, len(s.userVars.values))
 	sessionStates.UserVarTypes = make(map[string]*ptypes.FieldType, len(s.userVars.types))
-	s.userVars.lock.RLock()
-	defer s.userVars.lock.RUnlock()
 	for name, userVar := range s.userVars.values {
 		sessionStates.UserVars[name] = userVar.Clone()
 	}
 	for name, userVarType := range s.userVars.types {
 		sessionStates.UserVarTypes[name] = userVarType.Clone()
 	}
+	s.userVars.lock.RUnlock()
 
 	// Encode other session contexts.
 	sessionStates.PreparedStmtID = s.preparedStmtID
@@ -2328,11 +2328,9 @@ func (s *SessionVars) EncodeSessionStates(ctx context.Context, sessionStates *se
 // DecodeSessionStates restores session states from SessionStates.
 func (s *SessionVars) DecodeSessionStates(ctx context.Context, sessionStates *sessionstates.SessionStates) (err error) {
 	// Decode user-defined variables.
-	s.userVars.values = make(map[string]types.Datum, len(sessionStates.UserVars))
 	for name, userVar := range sessionStates.UserVars {
 		s.SetUserVarVal(name, *userVar.Clone())
 	}
-	s.userVars.types = make(map[string]*ptypes.FieldType, len(sessionStates.UserVarTypes))
 	for name, userVarType := range sessionStates.UserVarTypes {
 		s.SetUserVarType(name, userVarType.Clone())
 	}

sessionctx/variable/session_test.go

@@ -15,6 +15,8 @@
 package variable_test
 
 import (
+	"context"
+	"strconv"
 	"sync"
 	"testing"
 	"time"
@@ -25,10 +27,12 @@ import (
 	"github.com/pingcap/tidb/parser/auth"
 	"github.com/pingcap/tidb/parser/mysql"
 	plannercore "github.com/pingcap/tidb/planner/core"
+	"github.com/pingcap/tidb/sessionctx/sessionstates"
 	"github.com/pingcap/tidb/sessionctx/stmtctx"
 	"github.com/pingcap/tidb/sessionctx/variable"
 	"github.com/pingcap/tidb/testkit"
 	"github.com/pingcap/tidb/types"
+	util2 "github.com/pingcap/tidb/util"
 	"github.com/pingcap/tidb/util/chunk"
 	"github.com/pingcap/tidb/util/execdetails"
 	"github.com/pingcap/tidb/util/mock"
@@ -533,3 +537,35 @@ func TestPretectedTSList(t *testing.T) {
 	require.Equal(t, uint64(0), lst.GetMinProtectedTS(1))
 	require.Equal(t, 0, lst.Size())
 }
+
+func TestUserVarConcurrently(t *testing.T) {
+	sv := variable.NewSessionVars(nil)
+	ctx, cancel := context.WithTimeout(context.Background(), time.Second)
+	var wg util2.WaitGroupWrapper
+	wg.Run(func() {
+		for i := 0; ; i++ {
+			select {
+			case <-time.After(time.Millisecond):
+				name := strconv.Itoa(i)
+				sv.SetUserVarVal(name, types.Datum{})
+				sv.GetUserVarVal(name)
+			case <-ctx.Done():
+				return
+			}
+		}
+	})
+	wg.Run(func() {
+		for {
+			select {
+			case <-time.After(time.Millisecond):
+				var states sessionstates.SessionStates
+				require.NoError(t, sv.EncodeSessionStates(ctx, &states))
+				require.NoError(t, sv.DecodeSessionStates(ctx, &states))
+			case <-ctx.Done():
+				return
+			}
+		}
+	})
+	wg.Wait()
+	cancel()
+}