具有隐藏窗口的线程的线程消息循环？

Question

我有一个 Delphi 6 应用程序，它有一个线程专用于与使用 SendMessage() 和 WM_COPYDATA 消息与外部程序交互的外部应用程序进行通信。因此，我使用 AllocateHWND() 创建一个隐藏窗口来满足该需要，因为由于 SendMessage() 函数仅接受窗口句柄而不接受线程 ID，因此线程消息队列将无法工作。我不确定要在线程 Execute() 方法中放入什么内容。

我假设如果我使用 GetMessage() 循环或创建一个带有 WaitFor*() 函数调用的循环，线程将阻塞，因此线程的 WndProc() 将永远不会处理来自外部程序的 SendMessage() 消息正确的？如果是这样，放入 Execute() 循环的正确代码是什么，该循环不会不必要地消耗 CPU 周期，但一旦收到 WM_QUIT 消息就会退出？如有必要，我总是可以使用 Sleep() 进行循环，但我想知道是否有更好的方法。

Answer 1

AllocateHWnd()（更具体地说，MakeObjectInstance()）不是线程安全的，因此您必须小心使用它。最好直接使用 CreatWindow/Ex() （或者使用 AllocateHWnd() 的线程安全版本，例如 DSiAllocateHwnd()。

在任何在这种情况下，HWND 与创建它的线程上下文相关联，因此您必须在 Execute() 方法内创建和销毁 HWND ，而不是在线程的构造函数/析构函数中。此外，即使使用 SendMessage() 向您发送消息，它们也来自另一个进程，因此您的 不会处理它们。 >HWND 直到其所属线程执行消息检索操作，因此线程需要自己的消息循环。

您的 Execute() 方法应如下所示：

procedure TMyThread.Execute;
var
  Message: TMsg;
begin
  FWnd := ...; // create the HWND and tie it to WndProc()...
  try
    while not Terminated do
    begin
      if MsgWaitForMultipleObjects(0, nil^, False, 1000, QS_ALLINPUT) = WAIT_OBJECT_0 then
      begin
        while PeekMessage(Message, 0, 0, 0, PM_REMOVE) do
        begin
          TranslateMessage(Message);
          DispatchMessage(Message);
        end;
      end;
    end;
  finally
    // destroy FWnd...
  end;
end;

procedure TMyThread.WndProc(var Message: TMessage);
begin
  if Message.Msg = WM_COPYDATA then
  begin
    ...
    Message.Result := ...;
  end else
    Message.Result := DefWindowProc(FWnd, Message.Msg, Message.WParam, Message.LParam);
end;

或者：

// In Delphi XE2, a virtual TerminatedSet() method was added to TThread,
// which is called when TThread.Terminate() is called.  In earlier versions,
// use a custom method instead...

type
  TMyThread = class(TThread)
  private
    procedure Execute; override;
    {$IF RTLVersion >= 23}
    procedure TerminatedSet; override;
    {$IFEND}
  public
    {$IF RTLVersion < 23}
    procedure Terminate; reintroduce;
    {$IFEND}
  end;

procedure TMyThread.Execute;
var
  Message: TMsg;
begin
  FWnd := ...; // create the HWND and tie it to WndProc()...
  try
    while not Terminated do
    begin
      if WaitMessage then
      begin
        while PeekMessage(Message, 0, 0, 0, PM_REMOVE) do
        begin
          if Message.Msg = WM_QUIT then Break;
          TranslateMessage(Message);
          DispatchMessage(Message);
        end;
      end;
    end;
  finally
    // destroy FWnd...
  end;
end;

{$IF RTLVersion < 23}
procedure TMyThread.Terminate;
begin
  inherited Terminate;
  PostThreadMessage(ThreadID, WM_QUIT, 0, 0);
end;
{$ELSE}
procedure TMyThread.TerminatedSet;
begin
  PostThreadMessage(ThreadID, WM_QUIT, 0, 0);
end;
{$IFEND}

Answer 2

这是一个不需要 Classes.pas 的循环，仅依赖于 System.pas 来实现一些辅助函数、Windows.pas 来实现 Win32 API 函数以及 Messages.pas 来实现 WM_ 常量。

请注意，这里的窗口句柄是从工作线程创建和销毁的，但主线程会等待工作线程完成初始化。您可以推迟此等待，直到稍后真正需要窗口句柄时，这样主线程可能会同时执行一些工作，而工作线程会自行设置。

unit WorkerThread;

interface

implementation

uses
  Messages,
  Windows;

var
  ExitEvent, ThreadReadyEvent: THandle;
  ThreadId: TThreadID;
  ThreadHandle: THandle;
  WindowHandle: HWND;

function HandleCopyData(hWnd: HWND; Msg: UINT; wParam: WPARAM; lParam: LPARAM): LRESULT;
begin
  Result := 0; // handle it
end;

function HandleWmUser(hWnd: HWND; Msg: UINT; wParam: WPARAM; lParam: LPARAM): LRESULT;
// you may handle other messages as well - just an example of the WM_USER handling
begin
  Result := 0; // handle it
end;

function MyWindowProc(hWnd: HWND; Msg: UINT; wParam: WPARAM; lParam: LPARAM): LRESULT; stdcall;
begin
  if Msg = WM_COPYDATA then
  begin
    Result := HandleCopyData(hWnd, Msg, wParam, lParam);
  end else
  if Msg = WM_USER then
  begin
    // you may handle other messages as well - just an example of the WM_USER handling
    // if you have more than 2 differnt messag types, use the "case" switch
    Result := HandleWmUser(hWnd, Msg, wParam, lParam);
  end else
  begin
    Result := DefWindowProc(hWnd, Msg, wParam, lParam);
  end;
end;

const
  WindowClassName = 'MsgHelperWndClass';
  WindowClass: TWndClass = (
    style: 0;
    lpfnWndProc: @MyWindowProc;
    cbClsExtra: 0;
    cbWndExtra: 0;
    hInstance: 0;
    hIcon: 0;
    hCursor: 0;
    hbrBackground: 0;
    lpszMenuName: nil;
    lpszClassName: WindowClassName);

procedure CreateWindowFromThread;
var
  A: ATOM;
begin
  A := RegisterClass(WindowClass);
  WindowHandle := CreateWindowEx(WS_EX_TOOLWINDOW, WindowClassName, 'Message Helper Window', WS_POPUP, 0, 0, 0, 0, 0, 0, hInstance, nil);
end;

procedure FreeWindowFromThread;
var
  H: HWND;
begin
  H := WindowHandle;
  WindowHandle := 0;
  DestroyWindow(H);
  UnregisterClass(WindowClassName, hInstance);
end;

function ThreadFunc(P: Pointer): Integer;  //The worker thread main loop, windows handle initialization and finalization
const
  EventCount = 1;
var
  EventArray: array[0..EventCount-1] of THandle;
  R: Cardinal;
  M: TMsg;
begin
  Result := 0;
  CreateWindowFromThread;
  try
    EventArray[0] := ExitEvent; // you may add other events if you need - just enlarge the Events array
    SetEvent(ThreadReadyEvent);
    repeat
      R := MsgWaitForMultipleObjects(EventCount, EventArray, False, INFINITE, QS_ALLINPUT);
      if R = WAIT_OBJECT_0 + EventCount then
      begin
        while PeekMessage(M, WindowHandle, 0, 0, PM_REMOVE) do
        begin
          case M.Message of
             WM_QUIT:
               Break;
             else
                begin
                  TranslateMessage(M);
                  DispatchMessage(M);
                end;
          end;
        end;
        if M.Message = WM_QUIT then
          Break;
      end else
      if R = WAIT_OBJECT_0 then
      begin
        // we have the ExitEvent signaled - so the thread have to quit
        Break;
      end else
      if R = WAIT_TIMEOUT then
      begin
        // do nothing, the timeout should not have happened since we have the INFINITE timeout
      end else
      begin
        // some errror happened, or the wait was abandoned with WAIT_ABANDONED_0 to (WAIT_ABANDONED_0 + nCount– 1)
        // just exit the thread
        Break;
      end;
    until False;
  finally
    FreeWindowFromThread;
  end;
end;

procedure InitializeFromMainThread;
begin
  ExitEvent := CreateEvent(nil, False, False, nil);
  ThreadReadyEvent := CreateEvent(nil, False, False, nil);
  ThreadHandle := BeginThread(nil, 0, @ThreadFunc, nil, 0, ThreadId);
end;

procedure WaitUntilHelperThreadIsReady;
begin
  WaitForSingleObject(ThreadReadyEvent, INFINITE); // wait until the worker thread start running and initialize the main window
  CloseHandle(ThreadReadyEvent); // we won't need it any more
  ThreadReadyEvent := 0;
end;

procedure FinalizeFromMainThread;
begin
  SetEvent(ExitEvent); // we should call it AFTER terminate for the Terminated property would already be True when the tread exits from MsgWaitForMultipleObjects
  WaitForSingleObject(ThreadHandle, INFINITE);
  CloseHandle(ThreadHandle); ThreadHandle := 0;
  CloseHandle(ExitEvent); ExitEvent := 0;
end;

initialization
  InitializeFromMainThread;

  WaitUntilHelperThreadIsReady; // we can call it later, just before we need the window handle
finalization
  FinalizeFromMainThread;
end.