Java Data Objects

Multithreading

You may have a simple application that requires only a single transaction at a time. It would use a single PersistenceManager and may perform successive transactions using the associated Transaction instance. You may have only a single thread accessing the persistent instances and instances of the JDO interface, but you may want multiple threads to access instances. In this case, you need to inform the JDO implementation that multiple threads are accessing the JDO environment.

A JDO implementation is thread safe , which means that its behavior is predictable in the presence of multiple application threads. When the application accesses and modifies persistent or transactional fields of persistent instances, the PersistenceManager performs its operations as if the operations were serialized. It is free to serialize internal data structures and order multithreaded operations in any way it chooses. The only application-visible behavior is that operations might block indefinitely (but not infinitely) while other operations complete.

Synchronizing a PersistenceManager instance is a relatively expensive operation. Many applications do not need multiple threads using the same PersistenceManager instance. If your application has multiple threads accessing a PersistenceManager or the instances it manages (e.g., persistent or transactional instances of persistent classes, instances of Transaction or Query, query results, etc.), you need to notify the PersistenceManager that multiple ...