Is it possible to commit a transaction and start a new one without releasing the row locks?

I have a use case where I need to:

1. Update a row.
2. Persist the changes to disk, such that a system crash will not reverse it.
3. Update the same row that has not been modified by another transaction (a race condition).

How would I achieve this? Is it possible to commit a transaction and start a new one without releasing the row locks?

Answer

Postgres supports Advisory Locks, that can be hold over Session Lifetime.
If all your threads use these locks, you would be safe.