Re: Memory leak when internal pointer passed out as parameter

At about the time of 4/4/2007 4:20 AM, santosh stated the following:
Daniel Rudy wrote:
At about the time of 4/3/2007 11:52 AM, Mike stated the following:

<snip>

Rational Purify checked the code, and reported memory leak on foo1
when we allocate memory. I assum e that the compiler will allocate a
new block of memory when foo1 returns. Then the memory allocated
within foo1 will remain in the system heap forever. However I have no
way to verify it.

The allocated memory will be returned to the system heap when the
program exits, if there is a memory leak.

Nowhere does the C Standard guarantee this. Yes, modern memory
protected operating systems do reclaim a program's allocated memory
after the latter's termination, but C implementations exist on systems
that're not as sophisticated or capable. A conforming C program must
not make such assumptions.

I don't know what the C standard says about alot of things, so thank you
for pointing that out. I do know that on some machines, if you don't
free the memory when the program exits, the host OS will die. Those are
few and far between in this day and age.

You've also ignored the case of long-running processes like UNIX
deamons. Memory leaks in such programs can cause the system memory to
be slowly eaten up.

Excellent point. I had forgotten about that. The thing with Unix is
that if the process keeps allocating memory until there is no more, then
either the process will die by itself, or the host OS will forcibly kill it.

I have written a complete set of wrapper functions for malloc(3) and
mmap(2) that solves the problem. The code is fully re-entrant since
everything is a pointer. So when a thread terminates, everything that
thread allocated also goes away. It keeps track of it using a open
chained hash table of pointers returned by malloc(3) and mmap(2).

It's always better to explicitly free any memory when you're done with
it.

I agree completely.

--
Daniel Rudy

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