executor: avoid ProjectoinExec's goroutine leak (#14127)

executor/explain.go

@@ -17,6 +17,7 @@ import (
 	"context"
 
 	"github.com/cznic/mathutil"
+	"github.com/pingcap/errors"
 	"github.com/pingcap/tidb/planner/core"
 	"github.com/pingcap/tidb/util/chunk"
 )
@@ -70,23 +71,39 @@ func (e *ExplainExec) Next(ctx context.Context, req *chunk.Chunk) error {
 	return nil
 }
 
-func (e *ExplainExec) generateExplainInfo(ctx context.Context) ([][]string, error) {
+func (e *ExplainExec) generateExplainInfo(ctx context.Context) (rows [][]string, err error) {
+	closed := false
+	defer func() {
+		if !closed && e.analyzeExec != nil {
+			err = e.analyzeExec.Close()
+			closed = true
+		}
+	}()
 	if e.analyzeExec != nil {
 		chk := newFirstChunk(e.analyzeExec)
+		var nextErr, closeErr error
 		for {
-			err := e.analyzeExec.Next(ctx, chk)
-			if err != nil {
-				return nil, err
-			}
-			if chk.NumRows() == 0 {
+			nextErr = Next(ctx, e.analyzeExec, chk)
+			if nextErr != nil || chk.NumRows() == 0 {
 				break
 			}
 		}
-		if err := e.analyzeExec.Close(); err != nil {
+		closeErr = e.analyzeExec.Close()
+		closed = true
+		if nextErr != nil {
+			if closeErr != nil {
+				err = errors.New(nextErr.Error() + ", " + closeErr.Error())
+			} else {
+				err = nextErr
+			}
+		} else if closeErr != nil {
+			err = closeErr
+		}
+		if err != nil {
 			return nil, err
 		}
 	}
-	if err := e.explain.RenderResult(); err != nil {
+	if err = e.explain.RenderResult(); err != nil {
 		return nil, err
 	}
 	if e.analyzeExec != nil {

executor/explain_unit_test.go

@@ -0,0 +1,92 @@
+// Copyright 2019 PingCAP, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package executor
+
+import (
+	"context"
+	"errors"
+	"testing"
+
+	"github.com/pingcap/parser/mysql"
+	"github.com/pingcap/tidb/expression"
+	"github.com/pingcap/tidb/sessionctx/variable"
+	"github.com/pingcap/tidb/types"
+	"github.com/pingcap/tidb/util/chunk"
+	"github.com/pingcap/tidb/util/mock"
+)
+
+var (
+	_ Executor = &mockErrorOperator{}
+)
+
+type mockErrorOperator struct {
+	baseExecutor
+	toPanic bool
+	closed  bool
+}
+
+func (e *mockErrorOperator) Open(ctx context.Context) error {
+	return nil
+}
+
+func (e *mockErrorOperator) Next(ctx context.Context, req *chunk.Chunk) error {
+	if e.toPanic {
+		panic("next panic")
+	} else {
+		return errors.New("next error")
+	}
+}
+
+func (e *mockErrorOperator) Close() error {
+	e.closed = true
+	return errors.New("close error")
+}
+
+func getColumns() []*expression.Column {
+	return []*expression.Column{
+		{Index: 1, RetType: types.NewFieldType(mysql.TypeLonglong)},
+	}
+}
+
+// close() must be called after next() to avoid goroutines leak
+func TestExplainAnalyzeInvokeNextAndClose(t *testing.T) {
+	ctx := mock.NewContext()
+	ctx.GetSessionVars().InitChunkSize = variable.DefInitChunkSize
+	ctx.GetSessionVars().MaxChunkSize = variable.DefMaxChunkSize
+	schema := expression.NewSchema(getColumns()...)
+	baseExec := newBaseExecutor(ctx, schema, nil)
+	explainExec := &ExplainExec{
+		baseExecutor: baseExec,
+		explain:      nil,
+	}
+	// mockErrorOperator returns errors
+	mockOper := mockErrorOperator{baseExec, false, false}
+	explainExec.analyzeExec = &mockOper
+	tmpCtx := context.Background()
+	_, err := explainExec.generateExplainInfo(tmpCtx)
+
+	expectedStr := "next error, close error"
+	if err.Error() != expectedStr || !mockOper.closed {
+		t.Errorf(err.Error())
+	}
+	// mockErrorOperator panic
+	mockOper = mockErrorOperator{baseExec, true, false}
+	explainExec.analyzeExec = &mockOper
+	defer func() {
+		if panicErr := recover(); panicErr == nil || !mockOper.closed {
+			t.Errorf("panic test failed: without panic or close() is not called")
+		}
+	}()
+	_, err = explainExec.generateExplainInfo(tmpCtx)
+}