With the release of version 10.4 Sydney, Delphi has officially moved away from the ARC memory model in the mobile compilers. This was announced in 2018, there is some nice background info in this blog post by Marco Cantu.

So how do you do a quick check if your Delphi mobile code has ARC dependencies you should fix?

Tip #1 – Run on Windows with ReportMemoryLeaksOnShutDown := True

This instructs the FastMM memory manager to report memory leaks. Simply run your iOS or Android App on Windows (with the Windows Platform active), perform the usual actions an end-user would perform and close the application. Any memory leaks will be reported and should be fixed.

In your application source code add this line:

 
begin
  ReportMemoryLeaksOnShutdown := True;
  Application.Initialize;
  Application.CreateForm(TFormMain, FormMain);
  Application.Run;
end.

If you have a memory leak a message like this will popup after closing the application.

Tip #2 –  Search | Find In Files (Shift-Ctrl-F) for any “.Create” code

Most ARC (Automatic reference Counting) code should be changed to CTFF (Create Try Finally Free). Just check if there is a try-finally and a free directly after the .Create. Not all Create code needs a try-finally-free, as some instances are owned by their container, for instance in a TObjectList<T> that may take ownership of the instantiated object.

Change this ARC code

 
procedure DoSpellCheck;
var 
  Harry: TWizard;
begin
  Harry := TWizard.Create; 
  Harry.SpellCheck;
end; 

To this CTFF code

 
procedure DoSpellCheck; 
var 
  Harry: TWizard; 
begin
  Harry := TWizard.Create;
  try
    Harry.SpellCheck;
  finally
    Harry.Free;
  end;
end;

Some code can not be easily changed from ARC to CTFF, mostly due to the Free needing to be called at some unspecified time in the future, which for instance is common in multi-threaded code. If this applies to you then you could take a look at smart pointers in Spring4D using Shared.Make(TObject.Create), or take a look at the new custom managed records which where introduced in Delphi 10.4. Both options enable you to use ARC style freeing of resources, within the now default unified memory model.

Tip #3 – Use a tool to check for memory leaks

The code in tip #1 uses the built-in FastMM4 and is free. There is also a dual-license newer version FastMM5, both are however limited to Windows. Luckily there is a nice and simple free library called leakcheck that does this for all Delphi platforms. Alternatively, if detecting leaks in Windows only is preferred, the commercial DeLeaker has a lot of options and easy overview of memory leaks. A nice summary of these tools and more can be found in the blog post of Wagner Landgraf.

Tip #4 – Check for platform specific code

The short check for memory leaks under the Windows platform will skip platform specific code for Android and iOS, so you should check for compiler directive based platform dependencies {$IFDEF ANDROID}, {$IFDEF IOS}, but also for run-time dependencies like with TOSVersion.TPlatform.pfiOS and TOSVersion.TPlatform.pfAndroid. Note that the compiler directive AUTOREFCOUNT has been removed in Delphi 10.4, but its entirely possible you used this in your own code to check for ARC availablity.

Tip 5 – Check for weak references

These are mostly introduced to enable multiple references to instances without affecting reference count in combination with ARC. Do not just remove them, they can also be used for other reference counted data structures which may not have anything to do with ARC perse.

Even without ARC, reference counting still exists in Delphi. The compiler will still automagically reference count interfaces and strings. The same mechanism is also used for the new custom managed records.