My program never releases the memory back. Why?_问答_开发者

I have a MDI program. When It starts it takes 2-3MB of RAM. Then, in this program I create about 260 MDI child windows (each has a TStringGrid, a bitmap and some other controls) and display some data. The application needs about 500MB to load all those windows. If I close each MDI child manually, the application still uses 160MB of RAM. Why it doesn't return to few MB of RAM? Should I worry about this? 160MB it is A LOT for a system that has only 1GB or RAM!!

Note: I use the WORKIN开发者_运维问答G SET column in Task Manager to see RAM statistics. Maybe I need a better tool to read the RAM utilization. (Private Working Set is just a bit smaller than Working Set).

This is not a leak!

FastMM (set on aggressive) indicates no memory leak when I close the program. See my Answer post for additional evidence that it isn't a leak.

I release stuff

Many people told me that closing a child window only hides it. I know that. I use "Action:= caFree" to actually release the forms. Each form is responsible for releasing the controls it holds.

Answer

I have found that FastMM is responsible for this. See the answer I posted below.

Delphi 7, Win 7 32 bit

Similar posts:

Can memory be cleaned up?

When to call SetProcessWorkingSetSize? (Convincing the memory manager to release the memory)

Task Manager is not the right tool to detect memory leaks. Delphi allocates large blocks of memory and keeps them later for future use, so certain increase in allocated memory is expected even after you release all resources. Any other results (and more detailed answers) can be obtained only by using specialize memory analysis tools. AQTime is the first that comes to mind, or if you can find old but useful MemProof, it would help you a lot (MemProof is free and for memory analysis it's more handy than AQTime).

It is very well possible that FastMM does not show memory leaks upon application termination (for instance because all objects are TComponents that are owned, and the ownser frees them).
But in the mean time, while running those components can still be around, and not freed soon enough.

Did you use the FastMM unit that shows a form with the current memory usage?

< Edit >
This is the FastMMUsageTracker.pas in the directory ...\FastMM\Demos\Usage Tracker.
Use that unit, then call the ShowFastMMUsageTracker function in it. You can refresh that form every once in a while to see how your memory consumption grows. I have put a FastMMUsageTrackerProject sample on-line, including an update of FastMM4 that makes it easier to check and debug memory leaks:

the form in the FastMMUsageTracker unit is now resizable, and the controls in it anchor in the right way
there is a new FastMmBootstrapUnit unit making debugging specific memory leaks easier

Something I had at hand last week, was a 3rd party DLL, which was not written in Delphi.
The DLL had a memory leak using Windows GlobalAlloc calls, which are not tracked by FastMM.

NB: I'm about to post an update to FastMM on

--jeroen

Answer:

I just removed FastMM from my project and the program returned to few MB after freeing all those child windows. Many may argue that this is not a misbehavior and that FastMM is doing this in order to do some kind of kinky memory optimizations. They may be true. However, it may be good for MY application but it may not be good of other running applications.

So, at least we know who causes this. I worried to a whole day that may program is leaking RAM like an old bucket. I am relieved now.

UPDATE:

To confirm that this behavior is generated by FastMM (as suggested by Barry Kelly) I created a second program that allocated A LOT of RAM. As soon as Windows ran out of RAM, my program memory utilization returned to its original value.
(Note: I am not saying there is a bug in FastMM!)

My program is not leaking. Problem solved.

The main limitation of FastMM's memory leak tracing is that it can only run when you shut down the program. It could be that you're still holding references to objects or other data that gets cleaned up when you shut down the program, but stays around until then.

For example, when you close the MDI child windows, do you call Free or Release on them, or just make them disappear? If they're hidden but not freed, they'll still be in memory.

If you close an MDI form it is not freed automatically. Use Action = caFree (google for that) to make sure the form is also freed.