如何使AllocateHwnd线程安全？

Question

VCL组件设计为仅从应用程序的主线程使用.对于视觉组件,这从未给我带来任何困难.但是,我有时希望能够使用例如TTimer来自后台线程的非可视组件.或者确实只是创建一个隐藏的窗口.由于依赖,这是不安全的AllocateHwnd.现在,AllocateHwnd我理解的不是线程安全是设计的.

是否有一个简单的解决方案,允许我AllocateHwnd从后台线程使用？

Answer 1

这个问题可以这样解决:

1. 获得或实现的线程版本AllocateHwnd和DeallocateHwnd.
2. 替换VCL这些功能的不安全版本.

对于第1项,我使用了PrimožGabrijelcic的代码,如他在博客上关于该主题的文章所述.对于第2项,我只是使用在运行时修补代码的非常着名的技巧,并用无条件JMP指令替换不安全例程的开头,这些指令将执行重定向到线程安全函数.

将它们放在一起会产生以下单元.

(* Makes AllocateHwnd safe to call from threads. For example this makes TTimer
   safe to use from threads.  Include this unit as early as possible in your
   .dpr file.  It must come after any memory manager, but it must be included
   immediately after that before any included unit has an opportunity to call
   Classes.AllocateHwnd. *)
unit MakeAllocateHwndThreadsafe;

interface

implementation

{$IF CompilerVersion >= 23}{$DEFINE ScopedUnitNames}{$IFEND}
uses
  {$IFDEF ScopedUnitNames}System.SysUtils{$ELSE}SysUtils{$ENDIF},
  {$IFDEF ScopedUnitNames}System.Classes{$ELSE}Classes{$ENDIF},
  {$IFDEF ScopedUnitNames}Winapi.Windows{$ELSE}Windows{$ENDIF},
  {$IFDEF ScopedUnitNames}Winapi.Messages{$ELSE}Messages{$ENDIF};

const //DSiAllocateHwnd window extra data offsets
  GWL_METHODCODE = SizeOf(pointer) * 0;
  GWL_METHODDATA = SizeOf(pointer) * 1;

  //DSiAllocateHwnd hidden window (and window class) name
  CDSiHiddenWindowName = 'DSiUtilWindow';

var
  //DSiAllocateHwnd lock
  GDSiWndHandlerCritSect: TRTLCriticalSection;
  //Count of registered windows in this instance
  GDSiWndHandlerCount: integer;

//Class message dispatcher for the DSiUtilWindow class. Fetches instance's WndProc from
//the window extra data and calls it.
function DSiClassWndProc(Window: HWND; Message, WParam, LParam: longint): longint; stdcall;
var
  instanceWndProc: TMethod;
  msg            : TMessage;
begin
  {$IFDEF CPUX64}
  instanceWndProc.Code := pointer(GetWindowLongPtr(Window, GWL_METHODCODE));
  instanceWndProc.Data := pointer(GetWindowLongPtr(Window, GWL_METHODDATA));
  {$ELSE}
  instanceWndProc.Code := pointer(GetWindowLong(Window, GWL_METHODCODE));
  instanceWndProc.Data := pointer(GetWindowLong(Window, GWL_METHODDATA));
  {$ENDIF ~CPUX64}
  if Assigned(TWndMethod(instanceWndProc)) then
  begin
    msg.msg := Message;
    msg.wParam := WParam;
    msg.lParam := LParam;
    msg.Result := 0;
    TWndMethod(instanceWndProc)(msg);
    Result := msg.Result
  end
  else
    Result := DefWindowProc(Window, Message, WParam,LParam);
end; { DSiClassWndProc }

//Thread-safe AllocateHwnd.
//  @author  gabr [based on http://fidoforum.ru/pages/new46s35o217746.ru.delphi and
//                 TIcsWndHandler.AllocateHWnd from ICS v6 (http://www.overbyte.be)]
//  @since   2007-05-30
function DSiAllocateHWnd(wndProcMethod: TWndMethod): HWND;
var
  alreadyRegistered: boolean;
  tempClass        : TWndClass;
  utilWindowClass  : TWndClass;
begin
  Result := 0;
  FillChar(utilWindowClass, SizeOf(utilWindowClass), 0);
  EnterCriticalSection(GDSiWndHandlerCritSect);
  try
    alreadyRegistered := GetClassInfo(HInstance, CDSiHiddenWindowName, tempClass);
    if (not alreadyRegistered) or (tempClass.lpfnWndProc <> @DSiClassWndProc) then begin
      if alreadyRegistered then
        {$IFDEF ScopedUnitNames}Winapi.{$ENDIF}Windows.UnregisterClass(CDSiHiddenWindowName, HInstance);
      utilWindowClass.lpszClassName := CDSiHiddenWindowName;
      utilWindowClass.hInstance := HInstance;
      utilWindowClass.lpfnWndProc := @DSiClassWndProc;
      utilWindowClass.cbWndExtra := SizeOf(TMethod);
      if {$IFDEF ScopedUnitNames}Winapi.{$ENDIF}Windows.RegisterClass(utilWindowClass) = 0 then
        raise Exception.CreateFmt('Unable to register DSiWin32 hidden window class. %s',
          [SysErrorMessage(GetLastError)]);
    end;
    Result := CreateWindowEx(WS_EX_TOOLWINDOW, CDSiHiddenWindowName, '', WS_POPUP,
      0, 0, 0, 0, 0, 0, HInstance, nil);
    if Result = 0 then
      raise Exception.CreateFmt('Unable to create DSiWin32 hidden window. %s',
              [SysErrorMessage(GetLastError)]);
    {$IFDEF CPUX64}
    SetWindowLongPtr(Result, GWL_METHODDATA, NativeInt(TMethod(wndProcMethod).Data));
    SetWindowLongPtr(Result, GWL_METHODCODE, NativeInt(TMethod(wndProcMethod).Code));
    {$ELSE}
    SetWindowLong(Result, GWL_METHODDATA, cardinal(TMethod(wndProcMethod).Data));
    SetWindowLong(Result, GWL_METHODCODE, cardinal(TMethod(wndProcMethod).Code));
    {$ENDIF ~CPUX64}
    Inc(GDSiWndHandlerCount);
  finally LeaveCriticalSection(GDSiWndHandlerCritSect); end;
end; { DSiAllocateHWnd }

//Thread-safe DeallocateHwnd.
//  @author  gabr [based on http://fidoforum.ru/pages/new46s35o217746.ru.delphi and
//                 TIcsWndHandler.AllocateHWnd from ICS v6 (http://www.overbyte.be)]
//  @since   2007-05-30
procedure DSiDeallocateHWnd(wnd: HWND);
begin
  if wnd = 0 then
    Exit;
  DestroyWindow(wnd);
  EnterCriticalSection(GDSiWndHandlerCritSect);
  try
    Dec(GDSiWndHandlerCount);
    if GDSiWndHandlerCount <= 0 then
      {$IFDEF ScopedUnitNames}Winapi.{$ENDIF}Windows.UnregisterClass(CDSiHiddenWindowName, HInstance);
  finally LeaveCriticalSection(GDSiWndHandlerCritSect); end;
end; { DSiDeallocateHWnd }

procedure PatchCode(Address: Pointer; const NewCode; Size: Integer);
var
  OldProtect: DWORD;
begin
  if VirtualProtect(Address, Size, PAGE_EXECUTE_READWRITE, OldProtect) then begin
    Move(NewCode, Address^, Size);
    FlushInstructionCache(GetCurrentProcess, Address, Size);
    VirtualProtect(Address, Size, OldProtect, @OldProtect);
  end;
end;

type
  PInstruction = ^TInstruction;
  TInstruction = packed record
    Opcode: Byte;
    Offset: Integer;
  end;

procedure RedirectProcedure(OldAddress, NewAddress: Pointer);
var
  NewCode: TInstruction;
begin
  NewCode.Opcode := $E9;//jump relative
  NewCode.Offset := NativeInt(NewAddress)-NativeInt(OldAddress)-SizeOf(NewCode);
  PatchCode(OldAddress, NewCode, SizeOf(NewCode));
end;

initialization
  InitializeCriticalSection(GDSiWndHandlerCritSect);
  RedirectProcedure(@AllocateHWnd, @DSiAllocateHWnd);
  RedirectProcedure(@DeallocateHWnd, @DSiDeallocateHWnd);

finalization
  DeleteCriticalSection(GDSiWndHandlerCritSect);

end.

必须在.dpr文件的单元列表中尽早包含此单元.显然它不能出现在任何自定义内存管理器之前,但它应该在此之后立即出现.原因是必须在进行任何调用之前安装替换例程AllocateHwnd.

更新我已经合并了最新版本的Primož代码,他亲切地发给我.

Answer 2

不要TTimer在线程中使用,它永远不会安全.有线程:

1)使用SetTimer()手动消息循环.你不需要的HWND,如果你使用一个回调函数,但你还是要发送消息.

2)使用CreateWaitableTimer()然后调用WaitForSingleObject()循环直到定时器发出信号.

3)使用timeSetEvent(),这是一个多线程计时器.要小心,因为它的回调是在自己的线程中调用的,所以要确保你的回调函数是线程安全的,并且对你在该线程内调用的内容有限制.最好让它设置一个信号,你的真正的线程等待,然后在计时器外工作.