remove connection after close

conn.go

@@ -17,6 +17,9 @@ type managedConn struct {
 	killed bool
 	mu     sync.RWMutex
 
+	// callback function to be called after the connection is closed
+	afterClose func(*managedConn)
+
 	execStmtsCounter  int // count the number of exec calls in a transaction
 	queryStmtsCounter int // count the number of query calls in a transaction
 }
@@ -31,7 +34,7 @@ type managedConn struct {
 func (c *managedConn) BeginTx(ctx context.Context, opts driver.TxOptions) (driver.Tx, error) {
 	select {
 	case <-c.ctx.Done():
-		c.conn.Close()
+		c.close()
 		return nil, driver.ErrBadConn
 	default:
 	}
@@ -67,10 +70,11 @@ func (c *managedConn) BeginTx(ctx context.Context, opts driver.TxOptions) (drive
 	return tx, err
 }
 
-func newManagedConn(ctx context.Context, conn driver.Conn) *managedConn {
+func newManagedConn(ctx context.Context, conn driver.Conn, afterClose func(*managedConn)) *managedConn {
 	return &managedConn{
-		ctx:  ctx,
-		conn: conn,
+		ctx:        ctx,
+		conn:       conn,
+		afterClose: afterClose,
 	}
 }
 
@@ -121,7 +125,7 @@ func (c *managedConn) QueryContext(ctx context.Context, query string, args []dri
 func (c *managedConn) Prepare(query string) (driver.Stmt, error) {
 	select {
 	case <-c.ctx.Done():
-		c.conn.Close()
+		c.close()
 		return nil, driver.ErrBadConn
 	default:
 	}
@@ -133,7 +137,7 @@ func (c *managedConn) Prepare(query string) (driver.Stmt, error) {
 func (c *managedConn) Begin() (driver.Tx, error) {
 	select {
 	case <-c.ctx.Done():
-		c.conn.Close()
+		c.close()
 		return nil, driver.ErrBadConn
 	default:
 	}
@@ -143,7 +147,7 @@ func (c *managedConn) Begin() (driver.Tx, error) {
 func (c *managedConn) IsValid() bool {
 	select {
 	case <-c.ctx.Done():
-		c.conn.Close()
+		c.close()
 		return false
 	default:
 	}
@@ -170,7 +174,7 @@ func (c *managedConn) ResetSession(ctx context.Context) error {
 func (c *managedConn) Close() error {
 	c.mu.Lock()
 	defer c.mu.Unlock()
-	err := c.conn.Close()
+	err := c.close()
 
 	if err == nil {
 		c.killed = true
@@ -179,6 +183,13 @@ func (c *managedConn) Close() error {
 	return err
 }
 
+func (c *managedConn) close() error {
+	if c.afterClose != nil {
+		defer c.afterClose(c)
+	}
+	return c.conn.Close()
+}
+
 func (c *managedConn) GetReset() bool {
 	c.mu.RLock()
 	defer c.mu.RUnlock()

conn_test.go

@@ -128,7 +128,7 @@ var _ = Describe("PrometheusMetrics", func() {
 	`
 
 	It("Should emit the correct metrics", func() {
-		mc := newManagedConn(context.Background(), mockDriverConn{})
+		mc := newManagedConn(context.Background(), mockDriverConn{}, nil)
 
 		ctx := ContextWithExecLabels(context.Background(), map[string]string{"grpc_method": "method_1", "grpc_service": "service_1"})
 

driver.go

@@ -272,12 +272,23 @@ func (cg *chanGroup) Open() (driver.Conn, error) {
 		return conn, err
 	}
 
-	manConn := newManagedConn(cg.ctx, conn)
+	manConn := newManagedConn(cg.ctx, conn, cg.remove)
 	cg.conns = append(cg.conns, manConn)
 
 	return manConn, nil
 }
 
+func (cg *chanGroup) remove(conn *managedConn) {
+	cg.mu.Lock()
+	defer cg.mu.Unlock()
+	for i, c := range cg.conns {
+		if c == conn {
+			cg.conns = append(cg.conns[:i], cg.conns[i+1:]...)
+			return
+		}
+	}
+}
+
 func (cg *chanGroup) parseValues(vs url.Values) {
 	cg.mu.Lock()
 	defer cg.mu.Unlock()