我有一个任务要在后台运行,并且不中断GUI线程来检查新程序版本。
当应用程序启动时,它立即将一个线程排队等待15秒,然后执行其余代码。如果检查是在15秒之前手动触发的,则应终止现有的自动线程。如果在任何时候关闭了应用程序,则应尽快终止所有剩余线程。
在下面的示例中,我使用2分钟进行调试。
我现在的问题是,我尝试使用WaitFor
,Terminate
,FreeOnTerminate
和OnTerminated
进行的组合不会获得期望的结果。没有调用Destroy
并且出现内存泄漏,终止线程时应用程序挂起,或者出现Cannot terminate externally created thread
异常。
线程代码
unit unCheckThread;
interface
uses SysUtils, Classes, SyncObjs, Dialogs;
type
TCheckThread = class(TThread)
private
FDelayEvent: TEvent;
FDelay: Integer;
public
constructor Create(const ADelay: Integer);
destructor Destroy; override;
procedure Execute; override;
procedure TerminatedSet; override;
end;
implementation
{ TCheckThread }
constructor TCheckThread.Create(const ADelay: Integer);
begin
inherited Create(True);
FreeOnTerminate := False;
FDelay := ADelay;
FDelayEvent := TEvent.Create(nil, True, False, '');
end;
destructor TCheckThread.Destroy;
begin
FDelayEvent.Free;
inherited;
end;
procedure TCheckThread.Execute;
begin
FDelayEvent.WaitFor(MSecsPerSec * FDelay);
{ if another thread has checked while waiting for the delay, cancel this check }
if Terminated then Exit;
{ some long running code }
Sleep(10000);
if Terminated then Exit;
Synchronize(
procedure()
begin
MessageDlg('Thread completed', mtConfirmation, [mbOK], 0);
end);
end;
procedure TCheckThread.TerminatedSet;
begin
FDelayEvent.SetEvent;
end;
end.
UI
unit Unit1;
interface
uses
Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
Vcl.Controls, Vcl.Forms, Vcl.Dialogs, unCheckThread, Vcl.StdCtrls;
type
TForm1 = class(TForm)
Button1: TButton;
Button2: TButton;
procedure Button1Click(Sender: TObject);
procedure Button2Click(Sender: TObject);
procedure FormClose(Sender: TObject; var Action: TCloseAction);
procedure FormCreate(Sender: TObject);
private
{ Private declarations }
AThread: TCheckThread;
procedure onterminate(Sender: TObject);
public
{ Public declarations }
end;
var
Form1: TForm1;
implementation
{$R *.dfm}
procedure TForm1.Button1Click(Sender: TObject);
begin
if Assigned(AThread) then begin
AThread.Terminate;
// AThread.WaitFor; // ?
end;
AThread := TCheckThread.Create(0); // start immediately
AThread.OnTerminate := onterminate;
AThread.Start;
end;
procedure TForm1.Button2Click(Sender: TObject);
begin
Close;
end;
procedure TForm1.FormClose(Sender: TObject; var Action: TCloseAction);
begin
if Assigned(AThread) then begin
AThread.Terminate;
// AThread.WaitFor; // ??
end;
end;
procedure TForm1.FormCreate(Sender: TObject);
begin
AThread := TCheckThread.Create(SecsPerMin * 2); // wait for 2 mintues before starting
end;
procedure TForm1.onterminate(Sender: TObject);
begin
FreeAndNil(AThread);
end;
end.
答案 0 :(得分:4)
您无法中断Sleep()
,因此这不是调试的好选择,尤其是对于较长的时间间隔。您应该改为使用FDelayEvent.WaitFor()
。这样,线程可以在终止时快速“唤醒”。
此外,不要在Synchronize()
的末尾调用Execute()
,而应该使用OnTerminate
事件来完成线程完成时所需的任何操作。 OnTerminate
已与主UI线程同步。
例如,当该线程终止时,您可以使用OnTerminate
将AThread
变量设置为nil
,以使Assigned(AThread)
检查不会失败。您已经在尝试这样做,但是您不能从其Free
事件处理程序中安全地 OnTerminate
线程,因此您可以考虑使用FreeOnTerminate=True
来代替,或至少将Free
延迟到处理程序退出之后。
因此,我不建议在应用程序启动时创建延迟线程。请改用TTimer
。触发其OnTimer
事件时,然后创建一个非延迟线程。如果用户触发手动检查,只需禁用计时器。这样,您就不会浪费资源来创建仅处于空闲状态的线程,也不必担心将多个线程彼此同步。
话虽如此,请尝试以下类似操作:
unit unCheckThread;
interface
uses
Classes;
type
TCheckThread = class(TThread)
protected
procedure Execute; override;
public
constructor Create(AOnTerminate: TNotifyEvent);
end;
implementation
uses
SysUtils;
{ TCheckThread }
constructor TCheckThread.Create(AOnTerminate: TNotifyEvent);
begin
inherited Create(False);
FreeOnTerminate := False;
OnTerminate := AOnTerminate;
end;
procedure TCheckThread.Execute;
var
I: Integer;
begin
{ some long running code }
for I := 1 to 20 do
begin
if Terminated then Exit;
Sleep(500);
end;
end;
end.
unit Unit1;
interface
uses
Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, unCheckThread;
const
WM_FREE_THREAD = WM_APP + 1;
type
TForm1 = class(TForm)
Button1: TButton;
Button2: TButton;
Timer1: TTimer;
procedure Button1Click(Sender: TObject);
procedure Button2Click(Sender: TObject);
procedure FormCreate(Sender: TObject);
procedure FormDestroy(Sender: TObject);
procedure Timer1Timer(Sender: TObject);
private
{ Private declarations }
AThread: TCheckThread;
procedure ThreadFinished(Sender: TObject);
procedure StartThread;
procedure StopThread;
procedure WMFreeThread(var Message: TMessage); message WM_FREE_THREAD;
public
{ Public declarations }
end;
var
Form1: TForm1;
implementation
{$R *.dfm}
procedure TForm1.Button1Click(Sender: TObject);
begin
StartThread;
end;
procedure TForm1.Button2Click(Sender: TObject);
begin
Close;
end;
procedure TForm1.FormCreate(Sender: TObject);
begin
Timer1.Interval := 120000; // wait for 2 minutes before starting
Timer1.Enabled = True;
end;
procedure TForm1.FormDestroy(Sender: TObject);
begin
StopThread;
end;
procedure TForm1.StartThread;
begin
Timer1.Enabled := False;
if not Assigned(AThread) then
begin
AThread := TCheckThread.Create(ThreadFinished);
Button1.Enabled := False;
end;
end;
procedure TForm1.StopThread;
begin
if Assigned(AThread) then
begin
AThread.OnTerminate := nil;
AThread.Terminate;
AThread.WaitFor;
FreeAndNil(AThread);
end;
end;
procedure TForm1.ThreadFinished(Sender: TObject);
begin
AThread := nil;
// in 10.2 Tokyo and later, you can use TThread.ForceQueue() instead...
// TThread.ForceQueue(nil, Sender.Free);
PostMessage(Handle, WM_FREE_THREAD, 0, LPARAM(Sender));
MessageDlg('Thread completed', mtConfirmation, [mbOK], 0);
Button1.Enabled := True;
end;
procedure TForm1.Timer1Timer(Sender: TObject);
begin
Timer1.Enabled := False;
StartThread;
end;
procedure TForm1.WMFreeThread(var Message: TMessage);
begin
TObject(Message.LParam).Free;
end;
end.
答案 1 :(得分:1)
如果:
然后:
保留下面的代码行。
FreeOnTerminate := False;
“杀死” /终止线程(无论其状态如何)。
TerminateThread(AThread.Handle, 0);
TForm1
有/拥有AThread
,并且由于您的代码可以重新创建AThread
(先在FormCreate
中,然后在Button1Click
中),所以免费线程在每次终止后立即执行(当前,您在Button1Click
和FormClose
中执行此操作)。万一您在其他任何地方进行if Assigned(AThread)
,请使用FreeAndNil
(它将释放AThread
并将其设置为nil
,这样Assigned(AThread)
可以正确返回{{1 }}(使用您的代码结构终止并释放线程)。
False
FreeAndNil(AThread);
方法(上方)需要TerminateThread
(您在Winapi.Windows
的使用列表中拥有)。它代替了Unit1
。
如下所示:
AThread.Terminate