[fpc-pascal] Possible Memory Leak in TThread.Synchronize

[Tony Whyman]

I have been investigating a possible memory leak in a multi-threading 
Lazarus program compiled with 3.0.4 where the stack trace with heaptrc 
shows:

Heap dump by heaptrc unit
7014 memory blocks allocated : 131978472/131992352
7004 memory blocks freed     : 114543216/114557096
10 unfreed memory blocks : 17435256
True heap size : 19267584
True free heap : 1831200
Should be : 1831048
Call trace for block $00007FFFE2A9D0C0 size 96
   $000000000043B31A line 354 of ../inc/heap.inc
   $0000000000450FE8 line 888 of ../unix/cthreads.pp
   $000000000043DB9F line 294 of ../inc/thread.inc
   $00000000004AE6B4 line 322 of ../objpas/classes/classes.inc
   $00000000004AE754 line 344 of ../objpas/classes/classes.inc
   $00000000004AE7F0 line 357 of ../objpas/classes/classes.inc
   ....

Line 322 of classes.inc reads:

     FSynchronizeEntry^.SyncEvent := RtlEventCreate;

Hence the implication is that the SyncEvent is not being disposed of 
correctly. Later on TThread.DoneSynchronizeEvent reads

procedure TThread.DoneSynchronizeEvent;
   begin
     if not Assigned(FSynchronizeEntry) then
       Exit;

     RtlEventDestroy(FSynchronizeEntry^.SyncEvent);
     Dispose(FSynchronizeEntry);
     FSynchronizeEntry := Nil;
   end;

So no problem here it seems. However, investigating further, this is not 
the only place that a SynchronizeEvent is disposed of. At line 379 of 
classes.inc we see:

function CheckSynchronize(...)

and this ends with:

     else
       begin
       { for Queue entries we dispose the entry and raise the exception }
       Dispose(tmpentry);
       if Assigned(exceptobj) then
         raise exceptobj;
       end;
     tmpentry := PopThreadQueueHead;
     end;

The line "Dispose(tmpentry);" also disposes of a SynchronizeEvent but, 
unlike TThread.DoneSynchronizeEvent, there is no RtlEventDestroy.

Am I correct in pointing the finger here for the memory leak?

Tony Whyman

MWA