What is it called when a program allocates more and more memory but doesn't use the memory it allocates?

Answer 1

You are probably referring to a resource leak, however a resource leak specifically relates to programs that allocate memory on the heap (the free store) but fail to keep track of it. If we lose track of a heap allocation, the programmer cannot release that memory back to the system until the program terminates. The following is an example of a resource leak:

void f (unsigned x) {

void* p = malloc (x); // allocate x bytes // ... use memory

}

Each time we call this function we allocate another s bytes on the heap. But the function never releases that memory and because p is local to the function, we have no way of knowing where that memory was allocated (p will fall from scope when we return from the function). If we call this function often enough, we will eventually run out of memory.

To fix the problem, we must release the memory as soon as we are finished with it:

void f (unsigned x) {

void* p = malloc (x); // allocate x bytes // ... use memory

free (p); // release the memory

p = NULL; // zero the pointer

}

It is not necessary to zero a pointer when the pointer will fall from scope anyway, but it is considered good programming practice. What is important is that we release the memory it refers to before it falls from scope. Keeping our scopes as narrow as possible helps us to manage our resources more easily; the larger the scope, the more easily we can inadvertently introduce resource leaks, particularly when our code is maintained by several different programmers.

The problem you describe isn't necessarily a resource leak but it is clearly wasteful to allocate memory that is left unused even if we don't create a resource leak. Good programming practice dictates that we release memory as soon as we no longer require it, however allocating memory on an as-required basis can impact upon performance so it is not unusual for a programmer to allocate more memory than he needs, thus creating a reserve that can be used as and when required. Not using a reserve isn't in itself a problem, however we should endeavour to keep our reserves to a minimum and return all reserved memory to the system in a timely manner -- as soon as we no longer require it.