mORMot Open Source

docme

Member

Registered: 2014-03-07

Posts: 10

Merging FastMM4 and tsynlog data for better memory leak debugging

I've had too many weird memory leaks in my programs, so I had to dig around and put this together.  Thought it might help someone.  I was wondering if there is a better way of finding those bugs that think they are right to be there.  My idea was to collect the memory allocation number used by FastMM4 and save it in the .log file generated by tsynlog, so I can find 'when' as well as 'where' the memory was being allocated that wasn't being released.

This is in the main .dpr, uses clause and around the main begin section. 

uses
  FastMM4, syncommons, ...

...

{$Include FastMM4Options.inc} // must set FullDebugModeCallBacks in the used FastMM4Options.inc file!

{$ifdef debug}
{$ifdef FullDebugModeCallBacks}
procedure MyOnDebugGetMemFinish(APHeaderNewBlock: PFullDebugBlockHeader; ASize: NativeInt);
begin
// We can't use ILog, as it allocates memory = infinite loop!
//var ILog: ISynLog; begin  ILog := TSynLogDebug.Enter(self); //,pointer(rawutf8( inttostr(APHeaderNewBlock.AllocationNumber) + ' ' + inttostr(Asize) )));
  syncommons.FastMemAllocNumber := APHeaderNewBlock.AllocationNumber;
end;
{$endif}
{$endif}

begin
  {$ifdef debug}
  {$ifdef FullDebugModeCallBacks}
  OnDebugGetMemFinish := MyOnDebugGetMemFinish;
  {$endif}
  ReportMemoryLeaksOnShutdown := True; // seems lots!
  {$endif}

...

This piece of code I added to syncommons.pas just above the implementation reserved word.  No idea why I didn't put it into synlog.pas.

/// Code in .dpr sets event OnDebugGetMemFinish := MyOnDebugGetMemFinish; 
/// procedure MyOnDebugGetMemFinish(APHeaderNewBlock: PFullDebugBlockHeader; ASize: NativeInt); sets  syncommons.FastMemAllocNumber := APHeaderNewBlock.AllocationNumber;
/// Code in synLog.pas writes out current syncommons.FastMemAllocNumber before the line number in brackets near the end of the enter line.
var
  FastMemAllocNumber : Cardinal;

And the last piece to make it all actually do something in synlog.pas somewhere near the end of class procedure TSynMapFile.Log between a ' ' and a '('.  In my mormot1 version dated 20240808, it's line 2293.  SynLog.pas changed so often, I'm not sure if your one looks remotely the same as mine.

    if FastMemAllocNumber <> 0 then
      W.Add(FastMemAllocNumber);

Only thing left to do now is replace all begins with

var ILog: ISynLog; begin  ILog := TSynLogDebug.Enter(self);

and when the memory leak shows the allocation numbers, we can trace to them more accurately in our log file(s).