The validity of a visa while waiting to start a job is of one year. This visa cannot be renewed unless the holder has signed a new work contract or in case the visa is renewed for other reasons (eg. for family reasons). However, if in Italy there are members of the family or children born here, even if there is no one of the above mentioned requirements (an employment, in this case) the Administration cannot reject the application for the renewal of the visa if family ties in the country exist and are considered strong.
In any case, while unemployed, foreigners can renew the visa if they can prove to have any other legal source of income
Finally, the visa can be renewed even when a work contract is signed during renewal