2.12.2 Using shared memory

For many UNIX machines, ACUCOBOL-GT supports the ability to have multiple users share the same copy of a COBOL program's object code in memory. This conserves memory and can lead to improved system performance by reducing the amount of memory paging that the system must do.

Note: Use of shared memory is recommended only in cases where there is a problem with excessive swapping due to too many users for the amount of memory in the machine. If you aren't experiencing this problem, then using shared memory will not help. If you are having a problem with limited memory and excessive swapping, then the advantage of reduced swapping will usually more than make up for the overhead added by using shared memory. Note that the overhead for using shared memory may vary from machine to machine.

The UNIX code sharing facility is built on top of the UNIX System V shared memory facility. In order to use this code sharing, your machine must support shared memory in accordance with the UNIX System V Interface Definition (SVID) and must also have shared memory support enabled in its system kernel. Many UNIX vendors supply machines with shared memory already enabled, but others require that you reconfigure your kernel to use shared memory. Contact your UNIX vendor if you need additional information on this subject.

One easy way to tell if ACUCOBOL-GT supports code sharing on your machine is to check the files that come with the runtime system. If you receive a file called acushare, then you have the ability to share code. If you do not receive this file, then code sharing is not available on your machine (most likely due to the fact that your machine does not adequately support shared memory).

Note that COBOL overlays are not shared.

To share program code under ACUCOBOL-GT, follow these steps:

a. Install the ACUCOBOL-GT shared memory and license manager, acushare.

b. Edit your COBOL configuration file to indicate which programs you want to share (see section 2.12.2.1).

c. Start the acushare program. After it is started, you can use the program to perform other tasks. See section 2.12.3 for details.