Subj : Re: Multi-Thread and memory allocation error (or bug in 5.02).
To   : borland.public.cpp.borlandcpp
From : "Ed Mulroy [TeamB]" <ed@mulroyREMOVETHESECHARS.org>
Date : Fri Aug 29 2003 05:49 pm

I see nothing obviously wrong in the code and give no guarantees as to if my
ideas will solve the problem.  I also found the code did generated no
problem under BCB6 (XP Pro, 512M, PIII Mobile).

I assume that by this:

> If the creation and termination of the threads
>  removed the example runs fine.

you mean that you still did the allocation and de-allocation of the arrays.
If not then the test without threads didn't proove much since the code which
the OS complains of does not execute.


If it were my code, I try a couple of things.

Increase the stack size to something like 16384, comment out creation of all
but 2 of the 9 image lists (list2 through list7, list8 is already commented
out) and put in code to check the return values from _beginthreadNT and
SetThreadPriority.

If I were getting very frustrated I'd probably also code to detect if
WaitForSingleObject(mThread, INFINITE); returned WAIT_ABANDONED.

Obviously some of the changes I mentioned may be difficult for the
production code.  My goal in suggesting this is to find the problem or at
least generate a symptom related to a change so that the problem source can
be identified.

The RTL has undergone many changes in the 6 years since BC++ 5.02 was new.
If it still does not yield to debugging then I suggest you try one of these
two things.  (Note that I've not used BC++ 5.02 for anything multi-threaded
in years, so consider the source.)

Set up a main thread (main program thread) delete function.
Call that routine with the address of the int** array from the class.
Let that function do the array deletion of the int** array and the int*
arrays it contains instead of deleting in the destructor.
Somehow arrange for a slight delay between when the thread ends and the
deletion.

   or

Create a class which is essentially a container for the int** array and the
int* arrays it contains.  That class should do the allocation and deletion.
Use an auto_pointer of that class as a member variable in the TVMImageList
class.

Or you might try both (but of course not together).


I am curious.  Why do you do this:

  for (int j=0; j < mLength ; j++){
    array = thearray[j];
    delete[] array;
  }

Instead of this:

  for (int j=0; j < mLength ; j++)
    delete[] thearray[j];

..  Ed


> Martin Catney wrote in message
> news:3f4f7adf$1@newsgroups.borland.com...
>
> I am experience some problems with Borland 5.02 with
> multitheads and memory allocation and deallocation.
> The same code on Borland Builder 6 appears to work
> fine. I have included an example program which creates
> multiple instances of the same class then deletes them.
> The class constructor creates a new thread and allocates
> a large block of memory while the destructor
> deallocates the memory and terminates the thread.
>
> I get an access violation at 0x634b5e: read of address
> 0x4cdc058 when I run the example. This corresponds to
> the line delete[] array; in the class destructor. If the
> creation and termination of the threads is removed the
> example runs fine.
>
> Does anyone spot an obvious error in my example or is this a bug in the
> Run-Time Library?

.