Delphi - Recompiling application with 10.2.1 causes memory leaks?

Question

I just installed Delphi 10.2 Release 1. When I recompiled my applications and ran them, I get a lot of memory leaks. I had no memory leaks with 10.2 (without the update). I made no changes to the code either.

To verify, I created a simple blank application and put a few components on the form. No code. Ran the application and got memory leaks reported.

I wanted to highlight this (if only as a warning before you upgrade).

My questions:

1. Has anyone else seen this issue?
2. Is there something I need to or could be doing to get rid of this issue?

Note: I have logged an issue on quality portal, just in case this is a real issue: https://quality.embarcadero.com/browse/RSP-18774. In this ticket I have also attached the sample app.

Answer 1

After some investigation I found out that the callbacks being passed to TThread.CurrentThread.ForceQueue in TStyledControl.KillResourceLink are never executed because before any thread can handle them the application is ending and the TThread class destructor is destroying the list that still has unhandled callbacks.

I solved this by adding a call to CheckSynchronize at the end of FMX.Forms.DoneApplication which forces the callbacks to be executed which resolved the huge memory leak.

I don't know if this is the correct fix for the issue but it solved the memory leaks being reported.

Answer 2

I have the same problem using C++Builder 10.2.1 in FMX and in VCL applications.

If I enable CodeGuard, I get memory leaks on application exit.

I have a TThread with OnTerminate handler: if I put a breakpoint in this handler, when I close the program it is never called.

If I put CheckSynchronize() in the destructor of my main application form, the problem remains.

My solution was a "horrible" loop like this in the destructor of the main form:

__fastcall TForm3::~TForm3(void) {
    for(int i = 0; i < 10; i++) {
        Sleep(1);
        CheckSynchronize();
    }
}

This solution is not deterministic but may be used in your application in debug mode to avoid CodeGuard error messages.

Another solution is using the WaitFor() function if MyThread is a TThread object:

MyThread = new MyThreadClass();

and DeleteThisTh() is a method of this class, we can wait for terminated thread inside DeleteThisTh():

void MyThreadClass::DeleteThisTh(void) {
    Terminate();
    WaitFor();
    delete this;
}

In the OnTerminate event, I can clean my objects. Take note:

1. delete this is called after OnTerminate;
2. DeleteThisTh() lives in the main thread;