TClientDataSet CreateDataset内存泄漏

Question

我正在创建一个新组件，它继承自TClientDataSet，并导致内存泄漏。我创建了一个演示来重现错误(不需要共享myCustomComponent)。如何解决这个内存泄漏问题？

procedure TForm1.Button1Click(Sender: TObject);
begin
   ClientDataSet1.Close;
   ClientDataSet1.Tag := 1;
   ClientDataSet1.Open;
end;

procedure TForm1.ClientDataSet1BeforeOpen(DataSet: TDataSet);
begin
   if ClientDataSet1.Tag = 1 then
   begin
      ClientDataSet1.Tag := 0;
      ClientDataSet1.Fields.Clear;
      ClientDataSet1.FieldDefs.Clear;
      ClientDataSet1.FieldDefs.Add('Collection', ftString, 50);
      ClientDataSet1.FieldDefs.Find('Collection').CreateField(ClientDataSet1);
      ClientDataSet1.CreateDataSet;
   end;
end;

FastMM事件日志文件：

--------------------------------2017/6/19 12:00:21--------------------------------
A memory block has been leaked. The size is: 68

This block was allocated by thread 0x4FA8, and the stack trace (return addresses) at the time was:
418CD6 [FastMM4.pas][FastMM4][DebugAllocMem$qqri][9900]
407276 [System.pas][System][AllocMem$qqri][4557]
65F91B [Datasnap.DBClient.pas][Datasnap.DBClient][Dbclient.TCustomClientDataSet.AllocKeyBuffers$qqrv][3965]
6598AE [Datasnap.DBClient.pas][Datasnap.DBClient][Dbclient.TCustomClientDataSet.InternalOpen$qqrv][1514]
623BC8 [Data.DB.pas][Data.DB][Db.TDataSet.DoInternalOpen$qqrv][12527]
623C77 [Data.DB.pas][Data.DB][Db.TDataSet.OpenCursor$qqro][12556]
65885B [Datasnap.DBClient.pas][Datasnap.DBClient][Dbclient.TCustomClientDataSet.OpenCursor$qqro][1282]
623B2F [Data.DB.pas][Data.DB][Db.TDataSet.SetActive$qqro][12508]
62396B [Data.DB.pas][Data.DB][Db.TDataSet.Open$qqrv][12464]
65BE16 [Datasnap.DBClient.pas][Datasnap.DBClient][Dbclient.TCustomClientDataSet.CreateDataSet$qqrv][2342]
706827 [Unit1.pas][Unit1][TForm1.ClientDataSet1BeforeOpen$qqrp16Data.Db.TDataSet][64]

The block is currently used for an object of class: Unknown

The allocation number is: 1092

Current memory dump of 256 bytes starting at pointer address 7EF776F0:
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 F1 7F B4 7C
80 80 80 80 80 80 80 80 00 00 00 00 C1 70 F7 7E 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
73 04 00 00 D6 8C 41 00 76 72 40 00 1B F9 65 00 AE 98 65 00 C8 3B 62 00 77 3C 62 00 5B 88 65 00
2F 3B 62 00 6B 39 62 00 F4 65 70 00 D5 A7 53 00 A8 4F 00 00 A8 4F 00 00 AA 72 40 00 BE F5 60 00
AF F9 65 00 FA 9A 65 00 B8 3C 62 00 06 8C 65 00 9C 3B 62 00 F7 31 62 00 3C 8B 41 00 51 8B 41 00
29 7A 65 00 3C 00 00 00 00 00 00 00 69 F3 D9 86 E4 FB 71 00 80 80 80 80 80 80 80 80 80 80 80 80
80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80
.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .
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在尝试@victoria的代码时，我从fastMM那里得到了以下错误(尽管FastMM不会引发任何问题)，然后我意识到FastMM让我感到困惑。我重新引入了Open，并将该代码移到那里(没有调用继承或打开)，ReportMemoryLeaksOnShuntdown显示没有泄漏，但我不明白FastMM为什么会引发这种情况。

​

​

A memory block has been leaked. The size is: 68

This block was allocated by thread 0x4918, and the stack trace (return addresses) at the time was:
4DB29E54 
4DB28419 
4DB21AA9 
4DB1FB5B 
7711F11C [VirtualQuery]
33B8FD9 [GetFrameBasedStackTrace]
33B901C [GetFrameBasedStackTrace]
77983431 [Unknown function at RtlQueryPerformanceCounter]
33B9336 [GetRawStackTrace]
417A0E [FastMM4.pas][FastMM4][CalculateHeaderCheckSum$qqrp29Fastmm4.TFullDebugBlockHeader][9080]
417A1D [FastMM4.pas][FastMM4][UpdateHeaderAndFooterCheckSums$qqrp29Fastmm4.TFullDebugBlockHeader][9090]

The block is currently used for an object of class: Unknown

The allocation number is: 1060

Current memory dump of 256 bytes starting at pointer address 7EF76FA0:
3C 00 B4 4D 08 00 00 00 00 00 00 00 00 00 00 00 3F 00 00 00 00 80 80 80 80 80 80 80 80 80 80 80
80 80 80 80 80 80 80 80 43 00 80 80 80 80 80 80 80 80 80 80 80 80 80 80 01 00 00 00 0F 00 00 00
8C A3 AB 60 80 80 80 80 00 00 00 00 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
45 04 00 00 E8 A1 40 00 A3 AC 40 00 B5 F6 40 00 A0 BD 65 00 79 68 70 00 D5 A7 53 00 47 1F 55 00
55 2A 55 00 65 A2 53 00 38 70 3F 75 DD B4 04 74 18 49 00 00 18 49 00 00 AA 72 40 00 85 A2 40 00
3B BE 65 00 79 68 70 00 D5 A7 53 00 47 1F 55 00 55 2A 55 00 65 A2 53 00 38 70 3F 75 DD B4 04 74
89 B5 04 74 1B 00 00 00 E9 FD 01 00 04 D3 19 CB E4 FB 71 00 80 80 80 80 80 80 80 80 80 80 80 80
80 80 80 80 80 80 80 80 80 80 80 FB 2C E6 34 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80
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Answer 1

不要在BeforeOpen事件中定义和创建数据集。若要创建(并打开)内存中的数据集，请执行以下操作：

procedure TForm1.ButtonCreateClick(Sender: TObject);
begin
  ClientDataSet1.Close;
  ClientDataSet1.FieldDefs.Clear;
  ClientDataSet1.FieldDefs.Add('ID', ftInteger);
  ClientDataSet1.FieldDefs.Add('Collection', ftString, 50);
  ClientDataSet1.CreateDataSet;
end;

要添加记录，请执行：

procedure TForm1.ButtonAppendClick(Sender: TObject);
begin
  ClientDataSet1.Append;
  ClientDataSet1.FieldByName('ID').AsInteger := 1;
  ClientDataSet1.FieldByName('Collection').AsString := 'My collection';
  ClientDataSet1.Post;
end;

要编辑当前记录，请执行以下操作：

procedure TForm1.ButtonUpdateClick(Sender: TObject);
begin
  ClientDataSet1.Edit;
  ClientDataSet1.FieldByName('Collection').AsString := 'My collection upd.';
  ClientDataSet1.Post;
end;