Gem #43: Safe and Secure Software : Chapter 7, Safe Memory Management

by John Barnes

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The memory of the computer provides a vital part of the framework in which the program resides. The integrity of the memory contents is necessary for the health of the program. There is perhaps an analogy with human memory. If the memory is unreliable then the proper functioning of the person is seriously impaired.

There are two main problems with managing computer memory. One is that information can be lost by being improperly overwritten by other information. The other is that the memory itself can become filled and irrecoverable, so that no new information can be stored. This is the problem of memory leaks.

Memory leak is an insidious fault since it often does not show up for a long time. There was an example of a chemical control program that seemed to run flawlessly for several years. It was restarted every three months because of some external constraints (a crane had to be moved which necessitated stopping the plant). But the schedule for the crane changed and the program was then allowed to run for longer – it crashed after four months. There was a memory leak which slowly gnawed away at the free storage.

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Note: All chapters of this booklet will, in time, be available on the Ada 2005 home page.