为什么基于TComponent的接口实现泄漏内存？ [英] Why do interface implementations based on TComponent leak memory?

问题描述

此Delphi代码将显示TMyImplementation实例的内存泄漏：

This Delphi code will show a memory leak for an instance of TMyImplementation:

program LeakTest;

uses
  Classes;

type
  MyInterface = interface
  end;

  TMyImplementation = class(TComponent, MyInterface)
  end;

  TMyContainer = class(TObject)
  private
    FInt: MyInterface;
  public
    property Impl: MyInterface read FInt write FInt;
  end;

var
  C: TMyContainer;
begin
  ReportMemoryLeaksOnShutdown := True;

  C := TMyContainer.Create;
  C.Impl := TMyImplementation.Create(nil);
  C.Free;
end.

如果TComponent被替换为TInterfacedObject，构造函数更改为Create（），则泄漏消失。与TComponent有什么不同？

If TComponent is replaced by TInterfacedObject and the constructor changed to Create(), the leak disappears. What is different with TComponent here?

非常感谢您的答案。总结一下：很容易，但是错误的说：如果你使用的是接口，那么它们是引用计数的，因此它们被释放出来。实际上，实现接口的任何类都可以打破这个规则。 （将不会显示任何编译器提示或警告。）

Many thanks for the answers. To sum up: it is easy, but wrong, to say "If you are using interfaces, they are reference counted and hence they are freed for you." - Actually any class which implements an interface can break this rule. (And there will be no compiler hint or warning be shown.)

推荐答案

实现差异

• TComponent._Release 不释放您的实例。


• TInterfacedObject._Release 免费您的实例。



Differences in implementation

• TComponent._Release does not free your instance.
• TInterfacedObject._Release does free your instance.

也许有人可以铃声，但我认为这是 TComponent 不是用作引用计数对象方式我们通常使用接口。

Perhaps someone can chime in but my take on this is that TComponent is not meant to be used as a reference counted object the way we normally use interfaces.

function TComponent._Release: Integer;
begin
  if FVCLComObject = nil then
    Result := -1   // -1 indicates no reference counting is taking place
  else
    Result := IVCLComObject(FVCLComObject)._Release;
end;

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