This section presents the design principles that drive the decision
making process in the design and use of the OSCL active object
Dynamic data structures built around linked lists are employed throughout the architecture to the reduce the number of functions that can fail. Heuristics such as "The number of clients supported by a given server shall be limited only by system resource availability" and "The client supplies the memory resources for a transaction" lead the designer toward these data structures. Arrays and other fixed size data structures are used only at the highest levels of the application as a part of configuration. As a general rule, dynamic memory allocation from the global heap is limited to that performed by large grained objects which are instantiated infrequently and generally only at system startup. Run time dynamic allocation is deliberatly limited to implementation by individual servers, which maintain private memory pools and define explicit state driven behavior for exceptional conditions arising from memory allocation failures.
The messages referred to in this paper are like those found in many real-time operating systems environments. The message passing mechanism uses linked list data structures for queueing messages between threads into mailboxes, rather than using ring buffer style messages queues. Ring buffer style message queues have the disadvantage of being of fixed size, which implies that messages sent can fail if the ring buffer queue is full. This is an example of reducing the number of exceptions that can occur at the design level by employing linked lists.