CORBA 2.6 Programmer's Guide for Java

By using the ORB_CTRL_MODEL threading policy, servers can take advantage of multithreading
without doing any explicit programming. In certain situations, however, you might also find it desirable
to make a server explicitly spawn new threads. Such threads can coexist with POA-spawned threads.
When doing explicit multithreading in server programs, keep the following points in mind:
Do not make process-blocking calls from a thread. Such calls defeat the purpose of a multithreaded
process because the whole process is blocked for the duration of the call. The SQL/MP and
SQL/MX products do not support threads; therefore, all SQL calls are process-blocking calls.
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Operations directed to distributed objects are thread-blocking; nowait file I/O operations are also
thread-blocking. Such operations block only the calling thread, rather than the whole process. A
well-designed multithreaded program makes use of thread-blocking operations but not
process-blocking operations.
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Multiple active requests for the same object can be dispatched within multiple threads at the same
time. Therefore, you must code such portions as thread-safe (reentrant) code, protecting the
object from access by more than one thread at a time.
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Chapter 7. Managing Transactions Chapter 9. Designing Advanced
Applications