TObjectList memory leak?

I have this code in Delphi 7:

var

  Form1: TForm1;

  T: TObjectList;



implementation



{$R *.dfm}



procedure TForm1.Button1Click(Sender: TObject);

var

  I: Integer;

begin

 T := TObjectList.Create(True);

 for i := 1 to 10000 do begin

   T.Add(TPersistent.Create);

 end;

end;



procedure TForm1.Button2Click(Sender: TObject);

begin

 FreeAndNil(T);

end;

And this in Delphi 2009:

var

  Form1: TForm1;

  T: TObjectList<TPersistent>;



implementation



{$R *.dfm}



procedure TForm1.Button1Click(Sender: TObject);

var

  I: Integer;

begin

 T := TObjectList<TPersistent>.Create(True);

 for i := 1 to 10000 do begin

   T.Add(TPersistent.Create);

 end;

end;



procedure TForm1.Button2Click(Sender: TObject);

begin

  FreeAndNil(T);

end;

According to the Task Manager, when i free T in Delphi 7, all the memory that it used is freed, but in Delphi 2009, the memory is not free and even adds extra 30 kb. Am i missing something? or is there a memory leak in TObjectList in Delphi 2009?

asked Nov 21 '18 at 22:17

Ironcross

184

1

Ugh, Delphi 2009... not for this issue which obviously is none but for 100 other reasons. Get off that version as soon as you can. Especially if you want to use generics. They are terribly broken so are many other things.
– Stefan Glienke
Nov 22 '18 at 18:02

add a comment |

I have this code in Delphi 7:

var

  Form1: TForm1;

  T: TObjectList;



implementation



{$R *.dfm}



procedure TForm1.Button1Click(Sender: TObject);

var

  I: Integer;

begin

 T := TObjectList.Create(True);

 for i := 1 to 10000 do begin

   T.Add(TPersistent.Create);

 end;

end;



procedure TForm1.Button2Click(Sender: TObject);

begin

 FreeAndNil(T);

end;

And this in Delphi 2009:

var

  Form1: TForm1;

  T: TObjectList<TPersistent>;



implementation



{$R *.dfm}



procedure TForm1.Button1Click(Sender: TObject);

var

  I: Integer;

begin

 T := TObjectList<TPersistent>.Create(True);

 for i := 1 to 10000 do begin

   T.Add(TPersistent.Create);

 end;

end;



procedure TForm1.Button2Click(Sender: TObject);

begin

  FreeAndNil(T);

end;

asked Nov 21 '18 at 22:17

Ironcross

184

1

Ugh, Delphi 2009... not for this issue which obviously is none but for 100 other reasons. Get off that version as soon as you can. Especially if you want to use generics. They are terribly broken so are many other things.
– Stefan Glienke
Nov 22 '18 at 18:02

add a comment |

I have this code in Delphi 7:

var

  Form1: TForm1;

  T: TObjectList;



implementation



{$R *.dfm}



procedure TForm1.Button1Click(Sender: TObject);

var

  I: Integer;

begin

 T := TObjectList.Create(True);

 for i := 1 to 10000 do begin

   T.Add(TPersistent.Create);

 end;

end;



procedure TForm1.Button2Click(Sender: TObject);

begin

 FreeAndNil(T);

end;

And this in Delphi 2009:

var

  Form1: TForm1;

  T: TObjectList<TPersistent>;



implementation



{$R *.dfm}



procedure TForm1.Button1Click(Sender: TObject);

var

  I: Integer;

begin

 T := TObjectList<TPersistent>.Create(True);

 for i := 1 to 10000 do begin

   T.Add(TPersistent.Create);

 end;

end;



procedure TForm1.Button2Click(Sender: TObject);

begin

  FreeAndNil(T);

end;

asked Nov 21 '18 at 22:17

Ironcross

184

I have this code in Delphi 7:

var

  Form1: TForm1;

  T: TObjectList;



implementation



{$R *.dfm}



procedure TForm1.Button1Click(Sender: TObject);

var

  I: Integer;

begin

 T := TObjectList.Create(True);

 for i := 1 to 10000 do begin

   T.Add(TPersistent.Create);

 end;

end;



procedure TForm1.Button2Click(Sender: TObject);

begin

 FreeAndNil(T);

end;

And this in Delphi 2009:

var

  Form1: TForm1;

  T: TObjectList<TPersistent>;



implementation



{$R *.dfm}



procedure TForm1.Button1Click(Sender: TObject);

var

  I: Integer;

begin

 T := TObjectList<TPersistent>.Create(True);

 for i := 1 to 10000 do begin

   T.Add(TPersistent.Create);

 end;

end;



procedure TForm1.Button2Click(Sender: TObject);

begin

  FreeAndNil(T);

end;

delphi

asked Nov 21 '18 at 22:17

Ironcross

184

asked Nov 21 '18 at 22:17

Ironcross

184

asked Nov 21 '18 at 22:17

Ironcross

184

asked Nov 21 '18 at 22:17

Ironcross

184

asked Nov 21 '18 at 22:17

Ironcross

184

1

Ugh, Delphi 2009... not for this issue which obviously is none but for 100 other reasons. Get off that version as soon as you can. Especially if you want to use generics. They are terribly broken so are many other things.
– Stefan Glienke
Nov 22 '18 at 18:02

add a comment |

1

Ugh, Delphi 2009... not for this issue which obviously is none but for 100 other reasons. Get off that version as soon as you can. Especially if you want to use generics. They are terribly broken so are many other things.
– Stefan Glienke
Nov 22 '18 at 18:02

Ugh, Delphi 2009... not for this issue which obviously is none but for 100 other reasons. Get off that version as soon as you can. Especially if you want to use generics. They are terribly broken so are many other things.
– Stefan Glienke
Nov 22 '18 at 18:02

add a comment |

3 Answers
3

active

oldest

votes

Both versions do not leak. Your confusion stems from using the wrong tool to detect leaks. Memory managers tend to hang on to memory blocks that were recently used, and hope that they can be reused.

If you wish to detect memory leaks use the full FastMM library. That will show you that your code does not leak.

answered Nov 21 '18 at 22:49

David Heffernan

515k348151207

2

AFAIK, in one of the latest versions, FastMM's ReportMemoryLeaksOnShutDown was moved to System.pas, and can now be used without the explicit use of the FastMM unit.
– Rudy Velthuis
Nov 21 '18 at 23:20

That's true but there is no information beyond the number of blocks leaked. Using FastMM allows you to obtain stack traces at the point of allocoof each leaked block and many other powerful debugging tools.
– David Heffernan
Nov 22 '18 at 7:40

sure, with the explicit fastMM you get much better diagnostics. But I find it useful for a quick check.
– Rudy Velthuis
Nov 22 '18 at 7:47

add a comment |

Task Manager only reports the memory requested by the application through the Windows API. Delphi (just like every other compiler) has its own memory allocator that requests memory from Windows in chunks and then suballocates it as necessary. When you free a Delphi object, or a chunk of memory, it does not necessarily go back to Windows - Delphi's memory allocator simply marks the memory as free so it can be reused in subsequent memory requests. Windows knows nothing about that.

Try to create your own object and override its destructor - you can then put a breakpoint there to check that it indeed gets called.

edited Nov 22 '18 at 2:28

Remy Lebeau

332k18251443

answered Nov 21 '18 at 22:32

Dmitry Streblechenko

42.4k32760

1

Also note that modern Delphi versions have ReportMemoryLeaksOnShutdown to detect true memory leaks from Delphi's memory allocator, as only it can know what actually constitutes a leak or not. In Delphi 7, you would have to manually install FastMM to get that same behavior.
– Remy Lebeau
Nov 22 '18 at 2:31

add a comment |

There are no memory leaks. I tested both methods on Delphi XE6 and 10.2.3. I used: "ReportMemoryLeaksOnShutdown := DebugHook <> 0;" and to read memory GetProcessMemoryInfo -> WorkingSetSize.

edited Nov 22 '18 at 0:04

answered Nov 21 '18 at 23:58

janeks3

354

add a comment |

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3 Answers
3

active

oldest

votes

3 Answers
3

active

oldest

votes

Both versions do not leak. Your confusion stems from using the wrong tool to detect leaks. Memory managers tend to hang on to memory blocks that were recently used, and hope that they can be reused.

If you wish to detect memory leaks use the full FastMM library. That will show you that your code does not leak.

answered Nov 21 '18 at 22:49

David Heffernan

515k348151207

2

AFAIK, in one of the latest versions, FastMM's ReportMemoryLeaksOnShutDown was moved to System.pas, and can now be used without the explicit use of the FastMM unit.
– Rudy Velthuis
Nov 21 '18 at 23:20

That's true but there is no information beyond the number of blocks leaked. Using FastMM allows you to obtain stack traces at the point of allocoof each leaked block and many other powerful debugging tools.
– David Heffernan
Nov 22 '18 at 7:40

sure, with the explicit fastMM you get much better diagnostics. But I find it useful for a quick check.
– Rudy Velthuis
Nov 22 '18 at 7:47

add a comment |

Both versions do not leak. Your confusion stems from using the wrong tool to detect leaks. Memory managers tend to hang on to memory blocks that were recently used, and hope that they can be reused.

If you wish to detect memory leaks use the full FastMM library. That will show you that your code does not leak.

answered Nov 21 '18 at 22:49

David Heffernan

515k348151207

2

AFAIK, in one of the latest versions, FastMM's ReportMemoryLeaksOnShutDown was moved to System.pas, and can now be used without the explicit use of the FastMM unit.
– Rudy Velthuis
Nov 21 '18 at 23:20

That's true but there is no information beyond the number of blocks leaked. Using FastMM allows you to obtain stack traces at the point of allocoof each leaked block and many other powerful debugging tools.
– David Heffernan
Nov 22 '18 at 7:40

sure, with the explicit fastMM you get much better diagnostics. But I find it useful for a quick check.
– Rudy Velthuis
Nov 22 '18 at 7:47

add a comment |

Both versions do not leak. Your confusion stems from using the wrong tool to detect leaks. Memory managers tend to hang on to memory blocks that were recently used, and hope that they can be reused.

If you wish to detect memory leaks use the full FastMM library. That will show you that your code does not leak.

answered Nov 21 '18 at 22:49

David Heffernan

515k348151207

Both versions do not leak. Your confusion stems from using the wrong tool to detect leaks. Memory managers tend to hang on to memory blocks that were recently used, and hope that they can be reused.

If you wish to detect memory leaks use the full FastMM library. That will show you that your code does not leak.

answered Nov 21 '18 at 22:49

David Heffernan

515k348151207

answered Nov 21 '18 at 22:49

David Heffernan

515k348151207

answered Nov 21 '18 at 22:49

David Heffernan

515k348151207

answered Nov 21 '18 at 22:49

David Heffernan

515k348151207

2

AFAIK, in one of the latest versions, FastMM's ReportMemoryLeaksOnShutDown was moved to System.pas, and can now be used without the explicit use of the FastMM unit.
– Rudy Velthuis
Nov 21 '18 at 23:20

That's true but there is no information beyond the number of blocks leaked. Using FastMM allows you to obtain stack traces at the point of allocoof each leaked block and many other powerful debugging tools.
– David Heffernan
Nov 22 '18 at 7:40

sure, with the explicit fastMM you get much better diagnostics. But I find it useful for a quick check.
– Rudy Velthuis
Nov 22 '18 at 7:47

add a comment |

2

AFAIK, in one of the latest versions, FastMM's ReportMemoryLeaksOnShutDown was moved to System.pas, and can now be used without the explicit use of the FastMM unit.
– Rudy Velthuis
Nov 21 '18 at 23:20

That's true but there is no information beyond the number of blocks leaked. Using FastMM allows you to obtain stack traces at the point of allocoof each leaked block and many other powerful debugging tools.
– David Heffernan
Nov 22 '18 at 7:40

sure, with the explicit fastMM you get much better diagnostics. But I find it useful for a quick check.
– Rudy Velthuis
Nov 22 '18 at 7:47

AFAIK, in one of the latest versions, FastMM's ReportMemoryLeaksOnShutDown was moved to System.pas, and can now be used without the explicit use of the FastMM unit.
– Rudy Velthuis
Nov 21 '18 at 23:20

That's true but there is no information beyond the number of blocks leaked. Using FastMM allows you to obtain stack traces at the point of allocoof each leaked block and many other powerful debugging tools.
– David Heffernan
Nov 22 '18 at 7:40

sure, with the explicit fastMM you get much better diagnostics. But I find it useful for a quick check.
– Rudy Velthuis
Nov 22 '18 at 7:47

add a comment |

Try to create your own object and override its destructor - you can then put a breakpoint there to check that it indeed gets called.

edited Nov 22 '18 at 2:28

Remy Lebeau

332k18251443

answered Nov 21 '18 at 22:32

Dmitry Streblechenko

42.4k32760

1

Also note that modern Delphi versions have ReportMemoryLeaksOnShutdown to detect true memory leaks from Delphi's memory allocator, as only it can know what actually constitutes a leak or not. In Delphi 7, you would have to manually install FastMM to get that same behavior.
– Remy Lebeau
Nov 22 '18 at 2:31

add a comment |

Try to create your own object and override its destructor - you can then put a breakpoint there to check that it indeed gets called.

edited Nov 22 '18 at 2:28

Remy Lebeau

332k18251443

answered Nov 21 '18 at 22:32

Dmitry Streblechenko

42.4k32760

1

Also note that modern Delphi versions have ReportMemoryLeaksOnShutdown to detect true memory leaks from Delphi's memory allocator, as only it can know what actually constitutes a leak or not. In Delphi 7, you would have to manually install FastMM to get that same behavior.
– Remy Lebeau
Nov 22 '18 at 2:31

add a comment |

Try to create your own object and override its destructor - you can then put a breakpoint there to check that it indeed gets called.

edited Nov 22 '18 at 2:28

Remy Lebeau

332k18251443

answered Nov 21 '18 at 22:32

Dmitry Streblechenko

42.4k32760

Try to create your own object and override its destructor - you can then put a breakpoint there to check that it indeed gets called.

edited Nov 22 '18 at 2:28

Remy Lebeau

332k18251443

answered Nov 21 '18 at 22:32

Dmitry Streblechenko

42.4k32760

edited Nov 22 '18 at 2:28

Remy Lebeau

332k18251443

edited Nov 22 '18 at 2:28

Remy Lebeau

332k18251443

edited Nov 22 '18 at 2:28

Remy Lebeau

332k18251443

answered Nov 21 '18 at 22:32

Dmitry Streblechenko

42.4k32760

answered Nov 21 '18 at 22:32

Dmitry Streblechenko

42.4k32760

answered Nov 21 '18 at 22:32

Dmitry Streblechenko

42.4k32760

1

Also note that modern Delphi versions have ReportMemoryLeaksOnShutdown to detect true memory leaks from Delphi's memory allocator, as only it can know what actually constitutes a leak or not. In Delphi 7, you would have to manually install FastMM to get that same behavior.
– Remy Lebeau
Nov 22 '18 at 2:31

add a comment |

1

Also note that modern Delphi versions have ReportMemoryLeaksOnShutdown to detect true memory leaks from Delphi's memory allocator, as only it can know what actually constitutes a leak or not. In Delphi 7, you would have to manually install FastMM to get that same behavior.
– Remy Lebeau
Nov 22 '18 at 2:31

Also note that modern Delphi versions have ReportMemoryLeaksOnShutdown to detect true memory leaks from Delphi's memory allocator, as only it can know what actually constitutes a leak or not. In Delphi 7, you would have to manually install FastMM to get that same behavior.
– Remy Lebeau
Nov 22 '18 at 2:31

add a comment |

There are no memory leaks. I tested both methods on Delphi XE6 and 10.2.3. I used: "ReportMemoryLeaksOnShutdown := DebugHook <> 0;" and to read memory GetProcessMemoryInfo -> WorkingSetSize.

edited Nov 22 '18 at 0:04

answered Nov 21 '18 at 23:58

janeks3

354

add a comment |

There are no memory leaks. I tested both methods on Delphi XE6 and 10.2.3. I used: "ReportMemoryLeaksOnShutdown := DebugHook <> 0;" and to read memory GetProcessMemoryInfo -> WorkingSetSize.

edited Nov 22 '18 at 0:04

answered Nov 21 '18 at 23:58

janeks3

354

add a comment |

There are no memory leaks. I tested both methods on Delphi XE6 and 10.2.3. I used: "ReportMemoryLeaksOnShutdown := DebugHook <> 0;" and to read memory GetProcessMemoryInfo -> WorkingSetSize.

edited Nov 22 '18 at 0:04

answered Nov 21 '18 at 23:58

janeks3

354

There are no memory leaks. I tested both methods on Delphi XE6 and 10.2.3. I used: "ReportMemoryLeaksOnShutdown := DebugHook <> 0;" and to read memory GetProcessMemoryInfo -> WorkingSetSize.

edited Nov 22 '18 at 0:04

answered Nov 21 '18 at 23:58

janeks3

354

edited Nov 22 '18 at 0:04

answered Nov 21 '18 at 23:58

janeks3

354

answered Nov 21 '18 at 23:58

janeks3

354

answered Nov 21 '18 at 23:58

janeks3

354

add a comment |

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