CRE Programmer's Guide

CRE Services
Common Run-Time Environment (CRE) Programmer’s Guide—528146-004
2-37
Memory Organization
Memory Organization
This subsection describes the overall layout of memory for programs that use the
services of the CRE, and the data spaces that your program can use to share data.
TNS CRE Memory
In the TNS CRE, the data spaces that your program can use to share data are:
•
The extended stack
•
The user heap
•
Global data
The CRE allocates memory using the same layout in the OSS and Guardian
environments. For a given total amount of memory allocated to a process, however,
the amount of memory available in the OSS environment might be somewhat different
than the amount available to the same process running in the Guardian environment.
Overall Memory Organization
The TNS CRE, the language-specific run-time libraries, and your code share the same
address space for their data, although each has its own block of memory within that
space. The TNS CRE and run-time libraries allocate their data in the upper 32K words
of the user data segment and in extended memory. If your program specifies a small-
memory model, the TNS CRE allocates the heap in the lower 32K words of your user
data segment, just below the run-time stack. If your program specifies a large-memory
model or a wide-memory model, the TNS CRE allocates the heap as the last data
block in the extended segment.
If you use the TNS CRE, Binder ensures that the data structures for the language-
specific run-time libraries and for the TNS CRE do not overlay each other.
Your program maintains its data in the lower 32K words of the user data segment and
in extended memory.
Figure 2-14
on page 2-38 shows the overall memory organization for a program that
runs in a small-memory model and uses the TNS CRE. Figure 2-15
on page 2-39
shows the overall memory organization for a program that runs in a large-memory
model or a wide memory model, and that uses the TNS CRE. Shaded boxes in the
figures contain TNS CRE or language-specific run-time library data. Note that:
•
The TNS CRE and run-time libraries store their data in the upper 32K words of the
user data segment, beginning at the 32K-word boundary.
•
The TNS CRE allocates the user heap in the lower 32K words of the user data
segment just below the data stack in a small-memory model (Figure 2-14
on
page 2-38). The TNS CRE allocates the user heap in the extended memory
segment in a large-memory model and a wide-memory model (Figure 2-15
on
page 2-39).