fix memory leaks in PrepareStatementDB (#7142)

* fix memory leaks in PrepareStatementDB

* Fix CR:
1) Fix potential Segmentation Fault in Reset function
2) Setting db.Stmts to nil map when Close to avoid further using

* Add Test:
1) TestPreparedStmtConcurrentReset
2) TestPreparedStmtConcurrentClose

* Fix test, create new connection to keep away from other tests

---------

Co-authored-by: Zehui Chen <zehui@ssc-hn.com>

prepare_stmt.go

@@ -18,7 +18,6 @@ type Stmt struct {
 
 type PreparedStmtDB struct {
 	Stmts map[string]*Stmt
-	PreparedSQL []string
 	Mux   *sync.RWMutex
 	ConnPool
 }
@@ -28,7 +27,6 @@ func NewPreparedStmtDB(connPool ConnPool) *PreparedStmtDB {
 		ConnPool: connPool,
 		Stmts:    make(map[string]*Stmt),
 		Mux:      &sync.RWMutex{},
-		PreparedSQL: make([]string, 0, 100),
 	}
 }
 
@@ -48,12 +46,17 @@ func (db *PreparedStmtDB) Close() {
 	db.Mux.Lock()
 	defer db.Mux.Unlock()
 
-	for _, query := range db.PreparedSQL {
+	for _, stmt := range db.Stmts {
-		if stmt, ok := db.Stmts[query]; ok {
+		go func(s *Stmt) {
-			delete(db.Stmts, query)
+			// make sure the stmt must finish preparation first
-			go stmt.Close()
+			<-s.prepared
+			if s.Stmt != nil {
+				_ = s.Close()
 			}
+		}(stmt)
 	}
+	// setting db.Stmts to nil to avoid further using
+	db.Stmts = nil
 }
 
 func (sdb *PreparedStmtDB) Reset() {
@@ -61,9 +64,14 @@ func (sdb *PreparedStmtDB) Reset() {
 	defer sdb.Mux.Unlock()
 
 	for _, stmt := range sdb.Stmts {
-		go stmt.Close()
+		go func(s *Stmt) {
+			// make sure the stmt must finish preparation first
+			<-s.prepared
+			if s.Stmt != nil {
+				_ = s.Close()
+			}
+		}(stmt)
 	}
-	sdb.PreparedSQL = make([]string, 0, 100)
 	sdb.Stmts = make(map[string]*Stmt)
 }
 
@@ -93,7 +101,12 @@ func (db *PreparedStmtDB) prepare(ctx context.Context, conn ConnPool, isTransact
 
 		return *stmt, nil
 	}
-
+	// check db.Stmts first to avoid Segmentation Fault(setting value to nil map)
+	// which cause by calling Close and executing SQL concurrently
+	if db.Stmts == nil {
+		db.Mux.Unlock()
+		return Stmt{}, ErrInvalidDB
+	}
 	// cache preparing stmt first
 	cacheStmt := Stmt{Transaction: isTransaction, prepared: make(chan struct{})}
 	db.Stmts[query] = &cacheStmt
@@ -118,7 +131,6 @@ func (db *PreparedStmtDB) prepare(ctx context.Context, conn ConnPool, isTransact
 
 	db.Mux.Lock()
 	cacheStmt.Stmt = stmt
-	db.PreparedSQL = append(db.PreparedSQL, query)
 	db.Mux.Unlock()
 
 	return cacheStmt, nil

tests/prepared_stmt_test.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 	"sync"
+	"sync/atomic"
 	"testing"
 	"time"
 
@@ -167,3 +168,149 @@ func TestPreparedStmtReset(t *testing.T) {
 		t.Fatalf("prepared stmt should be empty")
 	}
 }
+
+func isUsingClosedConnError(err error) bool {
+	// https://github.com/golang/go/blob/e705a2d16e4ece77e08e80c168382cdb02890f5b/src/database/sql/sql.go#L2717
+	return err.Error() == "sql: statement is closed"
+}
+
+// TestPreparedStmtConcurrentReset test calling reset and executing SQL concurrently
+// this test making sure that the gorm would not get a Segmentation Fault, and the only error cause by this is using a closed Stmt
+func TestPreparedStmtConcurrentReset(t *testing.T) {
+	name := "prepared_stmt_concurrent_reset"
+	user := *GetUser(name, Config{})
+	createTx := DB.Session(&gorm.Session{}).Create(&user)
+	if createTx.Error != nil {
+		t.Fatalf("failed to prepare record due to %s, test cannot be continue", createTx.Error)
+	}
+
+	// create a new connection to keep away from other tests
+	tx, err := OpenTestConnection(&gorm.Config{PrepareStmt: true})
+	if err != nil {
+		t.Fatalf("failed to open test connection due to %s", err)
+	}
+	pdb, ok := tx.ConnPool.(*gorm.PreparedStmtDB)
+	if !ok {
+		t.Fatalf("should assign PreparedStatement Manager back to database when using PrepareStmt mode")
+	}
+
+	loopCount := 100
+	var wg sync.WaitGroup
+	var unexpectedError bool
+	writerFinish := make(chan struct{})
+
+	wg.Add(1)
+	go func(id uint) {
+		defer wg.Done()
+		defer close(writerFinish)
+
+		for j := 0; j < loopCount; j++ {
+			var tmp User
+			err := tx.Session(&gorm.Session{}).First(&tmp, id).Error
+			if err == nil || isUsingClosedConnError(err) {
+				continue
+			}
+			t.Errorf("failed to read user of id %d due to %s, there should not be error", id, err)
+			unexpectedError = true
+			break
+		}
+	}(user.ID)
+
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		<-writerFinish
+		pdb.Reset()
+	}()
+
+	wg.Wait()
+
+	if unexpectedError {
+		t.Fatalf("should is a unexpected error")
+	}
+}
+
+// TestPreparedStmtConcurrentClose test calling close and executing SQL concurrently
+// for example: one goroutine found error and just close the database, and others are executing SQL
+// this test making sure that the gorm would not get a Segmentation Fault,
+// and the only error cause by this is using a closed Stmt or gorm.ErrInvalidDB
+// and all of the goroutine must got gorm.ErrInvalidDB after database close
+func TestPreparedStmtConcurrentClose(t *testing.T) {
+	name := "prepared_stmt_concurrent_close"
+	user := *GetUser(name, Config{})
+	createTx := DB.Session(&gorm.Session{}).Create(&user)
+	if createTx.Error != nil {
+		t.Fatalf("failed to prepare record due to %s, test cannot be continue", createTx.Error)
+	}
+
+	// create a new connection to keep away from other tests
+	tx, err := OpenTestConnection(&gorm.Config{PrepareStmt: true})
+	if err != nil {
+		t.Fatalf("failed to open test connection due to %s", err)
+	}
+	pdb, ok := tx.ConnPool.(*gorm.PreparedStmtDB)
+	if !ok {
+		t.Fatalf("should assign PreparedStatement Manager back to database when using PrepareStmt mode")
+	}
+
+	loopCount := 100
+	var wg sync.WaitGroup
+	var lastErr error
+	closeValid := make(chan struct{}, loopCount)
+	closeStartIdx := loopCount / 2 // close the database at the middle of the execution
+	var lastRunIndex int
+	var closeFinishedAt int64
+
+	wg.Add(1)
+	go func(id uint) {
+		defer wg.Done()
+		defer close(closeValid)
+		for lastRunIndex = 1; lastRunIndex <= loopCount; lastRunIndex++ {
+			if lastRunIndex == closeStartIdx {
+				closeValid <- struct{}{}
+			}
+			var tmp User
+			now := time.Now().UnixNano()
+			err := tx.Session(&gorm.Session{}).First(&tmp, id).Error
+			if err == nil {
+				closeFinishedAt := atomic.LoadInt64(&closeFinishedAt)
+				if (closeFinishedAt != 0) && (now > closeFinishedAt) {
+					lastErr = errors.New("must got error after database closed")
+					break
+				}
+				continue
+			}
+			lastErr = err
+			break
+		}
+	}(user.ID)
+
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		for range closeValid {
+			for i := 0; i < loopCount; i++ {
+				pdb.Close() // the Close method must can be call multiple times
+				atomic.CompareAndSwapInt64(&closeFinishedAt, 0, time.Now().UnixNano())
+			}
+		}
+	}()
+
+	wg.Wait()
+	var tmp User
+	err = tx.Session(&gorm.Session{}).First(&tmp, user.ID).Error
+	if err != gorm.ErrInvalidDB {
+		t.Fatalf("must got a gorm.ErrInvalidDB while execution after db close, got %+v instead", err)
+	}
+
+	// must be error
+	if lastErr != gorm.ErrInvalidDB && !isUsingClosedConnError(lastErr) {
+		t.Fatalf("exp error gorm.ErrInvalidDB, got %+v instead", lastErr)
+	}
+	if lastRunIndex >= loopCount || lastRunIndex < closeStartIdx {
+		t.Fatalf("exp loop times between (closeStartIdx %d <=) and (< loopCount %d), got %d instead", closeStartIdx, loopCount, lastRunIndex)
+	}
+	if pdb.Stmts != nil {
+		t.Fatalf("stmts must be nil")
+	}
+}