Multi-threaded client apps

Are client connections to the database thread-safe?  Can each client thread
have its own connection?

What happens if multiple threads share one connection? For instance, can one
thread open a connection and another thread close it?
I realize this is probably not a good idea for many reasons, but our
architecture is dictating it.  

Marc Gunkel
mgunke@sandia.gov
505-844-3395