Out of virtual memory address space (Borland C++ Builder 6 program)

Question

I have problem with some application written under C++ Builder 6. After some time of running (week, month) the application crashes and closes without any error message. In my application log shortly before crash i get many "Out of memory" exceptions. I looked at the process when it was throwing out of memory exceptions (screenshot below) and it has lots of uncommitted private memory space. What can be a reason of such behavior?

I had such problem once, couple years ago. The reason for that was an option "use dynamic libraries" unchecked in linker options. When I checked it back the problem disappeared and vice versa. The test application which I made was just calling "new char[1000000]" and then delete. The memory was freed every time (no committed memory rise in windows task manager), but after some time I got out of memory, VMMap showed exactly the same thing. Lots of reserved private memory but most of it uncommitted.

Now the problem returned but I can't fix it the same way. I don't know if that was the reason but I had Builder 6 and 2010 istalled on the same machine. Now I just have Builder 6 and it seems that I cannot reproduce the error with test application like before. Ether way it seems that there is some memory manager error or something. CodeGuard doesn't show any memory leaks. When I create memory block with "new" it instantly shows in "memory commit size" and when delete the memory usage decreases, so I assume that the memory leaks are not the case, task manager doesn't show much "memory commit size".

Is there anything I can do? Is there any way I can release uncommitted memory? How to diagnose the problem any further?

The screenshot: https://i.sstatic.net/UKuTZ.jpg

Answer 1

I found a way to simulate this problem and solution.

for(int i=0; i<100; i++)
{
    char * b = new char[100000000];
    new char;
    delete b;
}

Borland memory manager reserves a block of memory which size is multiple of one page which is 4kB. When allocating memory size different than multiple of 4kB there is some free space which borland may use to allocate some other memory chunk. When the first chunk is deallocated the second is still keeping hole memory block reserved.

At first look the code should cause just 100B memory leak, but in fact it will cause memory allocation exception after less than 16 iterations.

I have found two solutions for this problem. One is FastMM, it works but also brings some troubles with it too. Second solution is to exchange borlndmm.dll with the one from Embarcadero Rad Studio 2010. I didn't test it thoroughly yet but it seems to work without any problem.

I should move the hole project to RAD 2010 but for some reasons I got stuck in Borland 6.