Oracle C++ Call Interface Programmer's Guide

Advanced Relational Techniques
Application-Provided Serialization In cases where there are multiple threads operating
on objects derived from an OCCI environment, you can chose to manage
serialization. The first step is to pass a value of THREADED_UNMUTEXED for the
createEnvironment mode. In this case the application must mutual exclusively
lock OCCI calls made on objects derived from the same OCCI environment. This
has the advantage that the mutex scheme can be optimized based on the application
design to gain greater concurrency.
When an OCCI environment is created in this mode, OCCI recognizes that the
application is running in a shared server environment, but that OCCI need not
acquire its internal mutexes. OCCI assumes that all calls to methods of objects
derived from that OCCI environment are serialized by the application. You can
achieve this two different ways:
■ Each thread has its own environment. That is, the environment and all objects
derived from it (connections, connection pools, statements, result sets, and so
on) are not shared across threads. In this case your application need not apply
any mutexes.
■ If the application shares an OCCI environment or any object derived from the
environment across threads, then it must serialize access to those objects (by
using a mutex, and so on) such that only one thread is calling an OCCI method
on any of those objects.
Basically, in both cases, no mutexes are acquired by OCCI. You must ensure that
only one OCCI call is in process on any object derived from the OCCI environment
at any given time when THREADED_UNMUTEXED is used.
Note:
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■ OCCI is optimized to reuse handles as much as possible. Since
each environment has its own heap, multiple environments
result in increased consumption of memory. Having multiple
environments may imply duplicating work with regard to
connections, connection pools, statements, and result set
objects. This will result in further memory consumption.
■ Having multiple connections to the server results in more
resource consumptions on the server and network. Having
multiple environments would normally entail more
connections.