ACSE/Presentation and ROSE Interface Programmer's Guide

58 Chapter 4

Programming Guide

5. Managing Multiple Connections

Before writing an application with multiple connections, you may need to

consider the following items:

• Execution mode

• Connection retry

• Resource constraints

Execution Mode

For using multiple connections, asynchronous mode is recommended.

Using multiple connections introduces factors that cannot be controlled

such as: when a task will complete, how long a task will take, or whether

or not tasks will complete sequentially. Factors affecting task completion

include network trafﬁc and the load on the system. Using synchronous

mode can introduce deadlock situations. For example, consider the

following scenario using ﬁrst synchronous then asynchronous

processing:

Two processes, an initiator and responder are each managing two

communication endpoints. The initiator side of the communication

endpoints are labeled A and B. The responder side of the communication

endpoints are labeled C and D (see Figure 4-1).

Communication endpoint A initiates a connection and transfers two data

packets over the connection to C. Two data packets are transferred over

the connection from C to A. Then endpoint A initiates a connect release

after it receives the two data packets.

Now, since the completion time of each task is not guaranteed (as

previously described), the following situation could occur:

• The initiator process is servicing endpoint B which has just sent out a

connection request (A_ASSOC_REQ) and is waiting for conﬁrmation

(A_ASSOC_CNF).

• Endpoint A received the ﬁrst data packet and is waiting for its turn to

receive the last data packet already on the queue before it sends out a

release request (A_RELEASE_REQ). At the same time, the responder

process is servicing endpoint C which has already sent its two data