Re: memory leakages with Ada?

[Nick Roberts <nickroberts@callnetuk.com>]

Larry Kilgallen wrote:

>In article <3c90af1e@news.starhub.net.sg>, "Calvin Ow" <calvow@cyberway.com.sg> writes:
>
>>Has Ada got any memory leakage problems like that of C?
>>
>
>Ada95 has several additional capabilities to guard against memory leaks.
>

Someone correct me if I'm wrong, but I think it would be more correct to 
put it this way: the Ada language makes provision for an implementation 
to provide garbage collection. If an Ada program is compiled/executed 
under an implementation that provides garbage collection, then this 
counts as a 'capability to guard against memory leaks'. If it provides 
_full_ garbage collection, this will normally provide complete 
protection against memory leaks.

However, all this is slightly academic, as (I am given to believe) there 
are no Ada implementations that provide garbage collection (apart from 
the ones which target the JVM, which is a somewhat different billie-can 
of anchovies anyway). Without GC, dynamic allocation will cause memory 
leakage (in the generally accepted meaning) unless: unused memory is 
freed explicitly (by the use of Unchecked_Deallocation); or, the 
algorithm uses (or tends to use) all or most dynamically allocated 
objects up until the end of the scope of the relevant access type's 
declaration (usually the end of the program's execution). This is pretty 
much the same situation as with C.

Of course, memory leakage can also be caused, in any programming 
language, by: faults in the compiler; programs doing low-level things, 
and getting it wrong. Typically, utility libraries which provide 
'containers' will need to do a lot of explicit freeing of memory; a bug 
can easily cause memory leakage.

>It is possible to bypass most checks in Ada, so one could encounter
>just as much trouble in Ada if one attempted to transliterate a C
>program into Ada while retaining every aspect of the C design.
>
>>Especially with the use of Pragma calls to C?
>>
>
>If you call from Ada to C, the portion that is written in C is
>fully empowered to leak all the memory it wants :-)  Thus the
>question of memory leaks when doing that boils down to an
>issue of whether the C code is well written.
>

Note that there are plenty of other kinds of problems associated with 
memory management that Ada (both the standard language and typical 
implementations) provides good protection against, and C does not.