ACSE/Presentation and ROSE Interface Programmer's Guide

Chapter 4 49

Programming Guide

2. Manage the A/P Environment

The ACSE/Presentation environment contains the necessary information

to establish and maintain an association. The primitives used to identify

this information are called attributes. See Appendix A, “AP_ENV Table

of Attributes” which describes the states and whether or not particular

attributes can be written to or read from.

Three A/P calls are used to manage information in the A/P environment:

• ap_init_env() establishes the environment and sets up default values

for many of the attributes. Note that the env_ﬁle variable in

ap_init_env() is ignored. Refer to the manpage for ap_env() for the

attribute default values.

• ap_set_env() is used to change a value of the speciﬁed attribute. To

change a list of attributes, you must use multiple ap_set_env() calls

(one for each attribute changed)

• ap_get_env() is used to read a value of a speciﬁed attribute.

When you use ap_get_env() for attributes which are stored as data

structures, memory is allocated for you. When you have ﬁnished using

the information from the data structure, must use ap_free() to free the

memory.

For memory allocated by your application, do not use ap_free().

Implement your own routines to free application-created memory

allocations.

A partial list of A/P attributes used that require allocating and

deallocating memory are: AP_PCDL, AP_PCDRL, and AP_LCL_PADDR.

Determine Initiator and Responder Roles

When you create your programs, decide which process will be initiating

and which one will be accepting associations.

By default, both processes may initiate and respond to a request. The

roles are set using the AP_ROLE_ALLOWED environment attribute.

However, when one process issues a connection request, it is established

as the initiator and may no longer receive connection indications. The

AP_ROLE_CURRENT is set to AP_INITIATOR.