onPut      []func()  // code (with db.mu held) run when conn is next returned
}

func (dc *driverConn) releaseConn(err error) {
	dc.db.putConn(dc, err, true)
}

func (dc *driverConn) removeOpenStmt(ds *driverStmt) {
	dc.Lock()
	defer dc.Unlock()
	delete(dc.openStmt, ds)
}

func (dc *driverConn) expired(timeout time.Duration) bool {
	if timeout <= 0 {
		return false
	}