Memory leak in the Win64 Delphi RTL during thread shutdown?

Question

For a long time I’ve noticed that the Win64 version of my server application leak memory. While the Win32 version works fine with a relatively stable memory footprint, the memor

Answer 1

In order to avoid the exception memoryleak trap, you could try to put an try/except around the FoobarProc. Maybe not for a definitive solution, but to see why the axception is raised in the first place.

I usually have something like this:

try
  FooBarProc()
except
  if IsFatalException(ExceptObject) then // checks for system exceptions like AV, invalidop etc
    OutputDebugstring(PChar(ExceptionToString(ExceptObject))) // or some other way of logging
end;

Answer 2

I use Delphi 10.2.3 and the problem described seems to still exist, at least under the following circumstances.

// Remark: My TFooThread is created within the 64 Bit DLL:

procedure TFooThread.Execute;
begin
 while not terminated do
  try
   ReadBlockingFromIndySocket();
   ProcessData();
  except on E:Exception do
   begin
    LogTheException(E.Message);
    // Leave loop and thread
    Abort;
   end
  end;
end;

This leaks memory whenever the loop/thread is left. MadExcept leak report shows that an exception object is not destroyed, in my case mostly an EIdConnClosedGracefully when the connection was closed remotely. The problem was found to be the Abort statement to leave the loop and thus the thread. Indications in the leak report seem to proof the observations of @RemyLebeau. Running the exact same code in the main program instead of the 64 Bit DLL does not leak any memory.

Solution: Exchange the Abort statement with Exit.

Conclusion: A thread execution function in a 64 Bit DLL must not be left with an exception (Abort is an exception as well), or else the exception causes a memory leak.

At least this worked for me.

Answer 3

A very simple work around is to re-use the thread and not create and destroy them. Threads are pretty expensive, you'll probably get a perf boost too... Kudos on the debugging though...