pg_dump a schema with data

PostgreSQL 9.4
Assume you do the following command which dumps all of the data associated with a schema:

pg_dump -schema=schemaName dbName > schemaName.out

Assume there are some 50 tables in the schema. Some of these tables have foreign keys to each other. During the dump of the schema, I would assume each table would be frozen/locked while it is being dumped. But what about tables that have associates to a table that is being written out. Will they be locked/frozen also. Or does postgresql lock up all of the tables within the schema while it is being dumped. Or are you just taking a risk that there might be miss associations between tables once the dump is complete.

My guess is that individual tables are locked/frozen while writing. I would also assume there might be relationship issues between related tables if there was a lot of writing or deleting during the dump.

Thanks,

Lance Campbell
University of Illinois