delphi - 压缩并发送 TFDDataset 的数据后释放 Form 时的 AV

Question

我在发布表单时有一个 AV，当我压缩 FireDAC 数据集的数据并将其发送到远程服务器时，它就会出现。

这是我用来压缩 TFDDataset 数据的代码:

function CompressDataset(Dataset: TFDDataset): TMemoryStream;
var Data: TMemoryStream;
    Compress: TZCompressionStream;
begin
  Result := TMemoryStream.Create;   
  Data := TMemoryStream.Create;
  try
    Compress := TZCompressionStream.Create(Result);
    Dataset.SaveToStream(Data, TFDStorageFormat.sfBinary);
    Data.Position := 0;
    Compress.CopyFrom(Data, Data.Size);
  finally
    Data.Free;
    Compress.Free;
  end;
  Result.Position := 0;
end;

这是将压缩数据发送到远程调用 (Datasnap) 的代码。

procedure TfrmRentFacturacion_Facturar.btnSendDesgloseClick(Sender: TObject);
var Stream: TMemoryStream;
begin
  if qryFacturacion_Desglose.State = dsEdit then qryFacturacion_Desglose.Post;

  Stream := CompressDataset(qryFacturacion_Desglose);
  try
    spActualizaDesglose.ParamByName('AStream').AsStream := Stream;
    spActualizaDesglose.ExecProc;
  finally
    Stream.Free;
  end;
end;

这段代码留下了一些不稳定的东西，最有可能是 TFDDataset qryFacturacion_Desglose，并在释放表单时引发 AV。但我不明白什么可能是错误的。

PS:感谢@J...建议检查调用堆栈，我找到了问题的根源。这是调用堆栈:

:000000000040E735 TObject.Free + $15
:00000000007F1123 TParamObject.Destroy + $43
:000000000041A155 TInterfacedObject._Release + $55
:000007FEFF2211CE ; C:\Windows\system32\oleaut32.dll
:0000000000459DAB VarClearDeep + $1B
:0000000000459E6B @VarClear + $1B
:0000000000459E7D @VarClr + $D
:00000000004149F4 @VarClr + $14
:0000000000414ACC @FinalizeArray + $BC
:00000000004162F1 @DynArrayClear + $61
:0000000000414B58 @FinalizeArray + $148
:0000000000414985 @FinalizeRecord + $75
:000000000040E82E TObject.CleanupInstance + $4E
:000000000040E450 TObject.FreeInstance + $10
:000000000040F1C1 @ClassDestroy + $11
:000000000051ED43 TCollectionItem.Destroy + $43
:000000000040E738 TObject.Free + $18
:000000000051F40A TCollection.Clear + $5A
:000000000051F1CD TCollection.Destroy + $2D
:000000000084A858 TFDParams.Destroy + $88
:0000000000838FD8 FDFree + $18
:000000000084A8BB TFDParams.RemRef + $2B
:0000000000B8C907 TFDCustomCommand.Destroy + $57
:000000000040E738 TObject.Free + $18
:00000000005419F3 TComponent.DestroyComponents + $93
:000000000054117F TComponent.Destroy + $2F
:0000000000B92A66 TFDCustomTableAdapter.Destroy + $86
:0000000000B9BE02 TFDRdbmsDataSet.Destroy + $C2
:000000000040E738 TObject.Free + $18
:00000000005419F3 TComponent.DestroyComponents + $93
:000000000054117F TComponent.Destroy + $2F
:00000000006039C2 TControl.Destroy + $192
:000000000060AA91 TWinControl.Destroy + $1B1
:0000000000797273 TScrollingWinControl.Destroy + $73
:0000000000798EB7 TCustomForm.Destroy + $1E7
:000000000040E738 TObject.Free + $18
:00000000007A1389 TCustomForm.CMRelease + $9
:000000000040EE81 TObject.Dispatch + $41
:0000000000607D56 TControl.WndProc + $386
:000000000060EC07 TWinControl.WndProc + $8E7
:000000000079ADB0 TCustomForm.WndProc + $910
:000000000060DE4C TWinControl.MainWndProc + $2C
:0000000000545056 StdWndProc + $26
:00000000777D9BBD ; C:\Windows\system32\USER32.dll
:00000000777D98C2 ; C:\Windows\system32\USER32.dll
:00000000007A8E84 TApplication.ProcessMessage + $134
:00000000007A8EF8 TApplication.HandleMessage + $18
:00000000007A9364 TApplication.Run + $F4
Impuestos.Impuestos
:00000000776B59CD ; C:\Windows\system32\kernel32.dll
:00000000778EA561 ; ntdll.dll

尝试释放对 Datasnap 服务器执行远程调用的 spActualizaDesglose TFDStoredProc 的参数 AStream 时，会发生 AV。

我更改了调用，因此在执行远程调用后不会释放原始数据流。

 procedure TfrmRentFacturacion_Facturar.btnSendDesgloseClick(Sender: TObject);
    var Stream: TMemoryStream;
    begin
      if qryFacturacion_Desglose.State = dsEdit then qryFacturacion_Desglose.Post;

      Stream := CompressDataset(qryFacturacion_Desglose);
      spActualizaDesglose.ParamByName('AStream').AsStream := Stream;
      spActualizaDesglose.ExecProc;
    end;

现在表单已经没有问题了，但是这样正确吗？这样会不会出现内存泄漏？

谢谢。

Answer 1

来自the manual page :

Setting the AsStream property sets the DataType property to ftStream if it is not one of the character string / byte string / BLOB data types. The assigned TStream object will be owned by this TFDParam. To explicitly control the ownership, use SetStream method.

强调我的。所以是的，将流分配给参数会赋予该流的参数所有权，并且当它本身被释放时，它会负责释放它(当它被拥有数据集组件的表单释放时，这是由数据集完成的)。

当您在此处释放流时:

Stream := CompressDataset(qryFacturacion_Desglose);
try
  spActualizaDesglose.ParamByName('AStream').AsStream := Stream;
  spActualizaDesglose.ExecProc;
finally
  Stream.Free;
end;

您正在销毁参数持有引用的对象，并且当参数对象第二次尝试释放它时，它会引发 AV。