multithreading - 如何在应用程序关闭时终止 Delphi 中的匿名线程？

Question

我有一个 Delphi 应用程序，它在某些 TTimer.OnTimer 事件上生成 6 个匿名线程。

如果我通过标题栏中的 X 按钮关闭应用程序，则会引发地址 $C0000005 处的访问冲突，并且 FastMM 报告泄露的 TAnonymousThread 对象。

在 Delphi 中，使用 TThread.CreateAnonymousThread() 方法释放 OnTimer 事件中创建的匿名线程的最佳方法是什么？

对我有用的解决方案:

创建匿名线程的包装器，在释放它们时终止它们。

type
  TAnonumousThreadPool = class sealed(TObject)
  strict private
    FThreadList: TThreadList;
    procedure TerminateRunningThreads;
    procedure AnonumousThreadTerminate(Sender: TObject);
  public
    destructor Destroy; override; final;
    procedure Start(const Procs: array of TProc);
  end;

{ TAnonumousThreadPool }

procedure TAnonumousThreadPool.Start(const Procs: array of TProc);
var
  T: TThread;
  n: Integer;
begin
  TerminateRunningThreads;

  FThreadList := TThreadList.Create;
  FThreadList.Duplicates := TDuplicates.dupError;

  for n := Low(Procs) to High(Procs) do
  begin
    T := TThread.CreateAnonymousThread(Procs[n]);
    TThread.NameThreadForDebugging(AnsiString('Test thread N:' + IntToStr(n) + ' TID:'), T.ThreadID);
    T.OnTerminate := AnonumousThreadTerminate;
    T.FreeOnTerminate := true;
    FThreadList.LockList;
    try
      FThreadList.Add(T);
    finally
      FThreadList.UnlockList;
    end;
    T.Start;
  end;
end;

procedure TAnonumousThreadPool.AnonumousThreadTerminate(Sender: TObject);
begin
  FThreadList.LockList;
  try
    FThreadList.Remove((Sender as TThread));
  finally
    FThreadList.UnlockList;
  end;
end;

procedure TAnonumousThreadPool.TerminateRunningThreads;
var
  L: TList;
  T: TThread;
begin
  if not Assigned(FThreadList) then
    Exit;
  L := FThreadList.LockList;
  try
    while L.Count > 0 do
    begin
      T := TThread(L[0]);
      T.OnTerminate := nil;
      L.Remove(L[0]);
      T.FreeOnTerminate := False;
      T.Terminate;
      T.Free;
    end;
  finally
    FThreadList.UnlockList;
  end;
  FThreadList.Free;
end;

destructor TAnonumousThreadPool.Destroy;
begin
  TerminateRunningThreads;
  inherited;
end;

这里是你如何调用它:

procedure TForm1.Button1Click(Sender: TObject);
begin
  FAnonymousThreadPool.Start([ // array of procedures to execute
    procedure{anonymous1}()
    var
      Http: THttpClient;
    begin
      Http := THttpClient.Create;
      try
        Http.CancelledCallback := function: Boolean
          begin
            Result := TThread.CurrentThread.CheckTerminated;
          end;
        Http.GetFile('http://mtgstudio.com/Screenshots/shot1.png', 'c:\1.jpg');
      finally
        Http.Free;
      end;
    end,

    procedure{anonymous2}()
    var
      Http: THttpClient;
    begin
      Http := THttpClient.Create;
      try
        Http.CancelledCallback := function: Boolean
          begin
            Result := TThread.CurrentThread.CheckTerminated;
          end;
        Http.GetFile('http://mtgstudio.com/Screenshots/shot2.png', 'c:\2.jpg');
      finally
        Http.Free;
      end;
    end
  ]);
end;

无内存泄漏，正确关闭且易于使用。

Answer 1

如果您想维护并控制线程的生命周期，则必须将 FreeOnTerminate 设置为 False。否则，在线程开始执行后引用该线程是错误的。这是因为一旦它开始执行，您就没有现成的方法来知道它是否已被释放。

调用CreateAnonymousThread创建一个将 FreeOnTerminate 设置为 True 的线程。

The thread is also marked as FreeOnTerminate, so you should not touch the returned instance after calling Start.

因此，默认情况下，您无法控制线程的生命周期。不过，您可以在调用 Start 之前立即将 FreeOnTerminate 设置为 False。像这样:

MyThread := TThread.CreateAnonymousThread(MyProc);
MyThread.FreeOnTerminate := False;
MyThread.Start;

但是，我不确定我会这样做。 CreateAnonymousThread 的设计是线程在终止时自动释放。我认为我个人要么遵循预期的设计，要么派生我自己的 TThread 后代。