尝试释放带有对象的 StringList 时的复杂问题使我的应用程序崩溃

Question

在Delphi10.4.2 win-32 VCL Application in Windows10中，我用这段代码收集了一些windows:[=14的句柄和程序路径=]

function GetPathFromPID(const PID: Cardinal): string;
var
  hProcess: THandle;
  Path: array[0..MAX_PATH - 1] of Char;
begin
  hProcess := Winapi.Windows.OpenProcess(Winapi.Windows.PROCESS_QUERY_INFORMATION or Winapi.Windows.PROCESS_VM_READ, False, PID);
  if hProcess <> 0 then
  try
    if Winapi.PsAPI.GetModuleFileNameEx(hProcess, 0, Path, Winapi.Windows.MAX_PATH) = 0 then
      RaiseLastOSError;
    Result := Path;
  finally
    Winapi.Windows.CloseHandle(hProcess)
  end
  else
    RaiseLastOSError;
end;

function EnumWinProc(wHandle: Winapi.Windows.HWND; aList: TStringList): Winapi.Windows.Bool; stdcall;
var
  strPath: string;
  IsAppMainWin: Boolean;
  ProcId: Cardinal;
begin
  IsAppMainWin := IsWindowVisible(wHandle)              and // Visible
    (GetWindow(wHandle, Winapi.Windows.GW_OWNER) = 0)   and // Not owned by other windows
    (GetParent(wHandle) = 0)                            and // Does not have any parent
    (GetWindowLong(wHandle, Winapi.Windows.GWL_EXSTYLE) and Winapi.Windows.WS_EX_TOOLWINDOW = 0); // Not a tool window

  if IsAppMainWin then
  begin
    GetWindowThreadProcessID(wHandle, ProcId);

    try
      strPath := GetPathFromPID(ProcId);
    except
      strPath := 'UnknownProgramPath';
    end;

    aList.AddObject(strPath, TObject(wHandle));
  end;

  Result := True;
end;

procedure ClearList(List: TStringList);
// 
var
  i: Integer;
begin
  // crash occurs here!
  for i := 0 to pred(List.Count) do
    List.Objects[i].Free;
  List.Clear;
end;

procedure TformMain.OutputAllAppWindows;
begin
  var sl := TStringList.Create;
  try
    sl.OwnsObjects := True;

    EnumWindows(@EnumWinProc, Winapi.Windows.LPARAM(sl));

    for var i := 0 to sl.Count - 1 do
    begin
      CodeSite.Send('window handle', Winapi.Windows.HWND(sl.Objects[i]));
      CodeSite.Send('program-path sl[i]', sl[i]);
    end;
    ClearList(sl); // EDIT: forgot this line!
  finally
    sl.Free; 
  end;
end;

EurekaLog 报告崩溃：

2.1 Date : Sat, 31 Jul 2021 22:36:53 +0200
2.2 Address : 005509D2
2.5 Type : EInvalidPointer
2.6 Message : Application made attempt to free invalid or unknown memory block: [=11=]010AE2 OBJECT [?] 0 bytes.
2.7 ID : B5002468
2.8 Count : 1
2.11 Sent : 0

这是在 EurekaLog 调用堆栈的顶部：

Answer 1

这里有两个问题：

首先，您将整数作为字符串列表中的对象，因此您不能将这些“对象”视为对象，因为它们不是。

特别是，没有任何东西可以释放，你不能释放这些“对象”；这相当于做 TObject(some random pointer).Free.

其次，如果你确实在列表中放置了真实的对象，你仍然会有一个错误，因为你会先自己释放它们而不是 niling 它们的引用，因此字符串列表的析构函数将尝试“销毁”这些悬挂指针指向的东西。再次，糟糕。

尝试释放带有对象的 StringList 时的复杂问题使我的应用程序崩溃

Complex problem when trying to free a StringList with objects crashes my app

delphi

winapi

memory-management

delphi-10.4-sydney