Thread Destroy with no corresponding Thread Create?

[alogrep 0]

HI

In the following code I put 2 breakpoints at the beginning of Thread.Create and of Thread.Destroy.

I noticed that in all cases except one the sequence Crate/Destroy is executed in the correct order.

But in one case, Destroy is called twice in a row.

Does anybody have an idea as to why? 

Constructor SendThread.Create(afmods:modslist; atablename: string;uniquenumber: int64;asavedir,adbase: string);
begin
  inherited create(false);
  FreeOnTerminate:=true;
  fmods:=afmods;
  tablename:=atablename;
  uniq:=uniquenumber;
  dbase:=adbase;
  savedir:=asavedir;
  sstream:=TStringstream.create;

end;

Destructor SendThread.Destroy;
begin
  sstream.free;
  inherited Destroy;
end;

procedure SendThread.Execute;
var
  s,last1: string;
  l,i,n,modindex: integer;
  done: boolean;
  t: textfile;
begin
   if length(fmods)<=0 then
     exit;
 modindex:=getmodindex(inttostr(uniq),fmods);
 with fmods[modindex] do begin
// s:=format('%-11s',[fmods[high(fmods)].val]);
// sStream.writestring(s);
  for l:=0 to high(mods) do begin
    sstream.writestring(format('%4s',[inttostr(mods[l].fieldpos)]));
    sstream.writestring(format('%10d',[length(mods[l].val)]));
    sStream.writestring(mods[l].val);
  END;
  mods:=Nil;
 end;
 sStream.position:=0;
 s:=Format('%.*d',[13, uniq]);
 s:= savedir+'\'+s+'$'+trim(copy(dbase,Lastdelimiter('\',dbase)+1,10))+'-'+tablename+'.db';
 sStream.savetofile(s);
 last1:=inttostr(Lastuniquenumber);
 sStream.clear;
 sstream.writestring(format('%4s',['0']));
 sstream.writestring(format('%10d',[length(last1)]));
 sStream.writestring(last1);
 s:=Format('%.*d',[13, uniq]);
 s:= savedir+'\'+s+'$pos-'+tablename+'.db';
 sStream.savetofile(s);
end;

 

[Der schöne Günther 306]

In all cases? What are those cases? Can you provide a minimal example (that actually compiles) with all your test cases?

[Remy Lebeau 1260]

Why is the code creating the TStringStream object in the constructor and destroying it in the destructor, instead of just using it locally inside of Execute()?  Do other threads need access to the TStringStream? If not, then it doesn't need to be a class member.

[aehimself 388]

If you have FreeOnTerminate := True and you call .Free, you can have 2 destructors but one will raise an AV as you are .Free.ing the StringStream instead of FreeAndNil.

[David Heffernan 2300]

Defect in your code, but in the code you didn't show. 

[Brian Evans 83]

Look at and compare the call stacks between the multiple hits of the breakpoint.