As the figure shows, the changes made by an autonomous transaction become visible to another transaction whenever the autonomous transaction commits. The changes also become visible to the major transaction if it resumes, but only if its isolation level is set to READ COMMITTED (the default).
When you set the isolation level of the major transaction to SERIALIZABLE, as shown, the changes made by its autonomous transactions are not visible to the major transaction when it resumes:
SET TRANSACTION ISOLATION LEVEL SERIALIZABLE;
Figure: Transaction Visibility