終止線程變量，並將其設置爲NULL

Question

當TThread後代的工作我基本上有一個選擇：

• 設置FreeOnTerminate到true它刪除我的TThread後代對象，但不會將其設置爲NULL
• 做手動，並通過自己刪除它的所有爛攤子

我基本上需要的是一種方式來確定線程是否正在運行，所以我做了以下：

//------------------------------------------------------------------------------ 
// Thread descendant 
//------------------------------------------------------------------------------ 
class TMyThread : public TThread 
    { 
    private: UnicodeString StatusLine; // Used for Synchronize function 

       void __fastcall UpdateGUI(); 
    protected: virtual void __fastcall Execute(); 
    public:     __fastcall TMyThread(); 
    }; 
//------------------------------------------------------------------------------ 
TMyThread *MyThread; 
//------------------------------------------------------------------------------ 

// Thread constructor 
__fastcall TMyThread::TMyThread() : TThread(true) 
{ 
FreeOnTerminate = false; 
Priority  = tpNormal; 
} 

// Synchronize function for Form1 
void __fastcall TMyThread::UpdateGUI() 
{ 
Form1->Label1 = StatusLine; 
} 

// Execute code 
void __fastcall TMyThread::Execute() 
{ 
Sleep(2000); 
StatusLine = "I am almost done!"; 
Synchronize(&UpdateGUI); 
} 

// Thread terminate, delete object, set to NULL 
void __fastcall TForm1::ThreadTerminateIfDone(TMyThread *T) 
{ 
if (T != NULL && WaitForSingleObject(reinterpret_cast<void*>(T->Handle),0) == WAIT_OBJECT_0) 
    { 
    T->Terminate(); 
    T->WaitFor(); 
    delete T; 
    T = NULL; 
    } 
} 

// And initialization part which needs to check if thread is already running 
void __fastcall TForm1::StartOrRestartThread(TObject *Sender) 
{ 
// Remove old thread if done 
ThreadTerminateIfDone(MyThread); 

// Check if thread is running - NULL = not running and terminated or uninitialized 
if (MyThread == NULL) 
    { 
    MyThread = new TMyThread(); 
    MyThread->Start(); 
    } 
else 
    { 
    Application->MessageBox(L"Thread is still running please wait!", L"Error", MB_OK); 
    } 
} 

此代碼按原樣運行。我的問題是：

• 有沒有辦法簡化這個？我需要在完成後將MyThread設置爲NULL，以便在下次調用啓動/重新啓動之前，對象不在周圍。這不能用FreeOnTerminate設置爲true來完成，因爲它會刪除對象。我只能嘗試訪問對象，然後生成異常（我可以捕捉，但它是愚蠢的）。我真的只需要知道在我初始化或重新啓動MyThread之前是否執行了執行。

• 我可以重新啓動線程而不終止它（我不需要在程序結束之前刪除對象） - 如果我啓動線程，我會得到「無法在運行或掛起的線程上調用啓動」異常。

Answer 1

你ThreadTerminateIfDone()功能需要通過參考拿線程指針，否則將無法設置指向正確NULL：

void __fastcall TForm1::ThreadTerminateIfDone(TMyThread* &T) 

隨着中說，如果使用線程的OnTerminate事件來跟蹤線程是否正在運行，則可以完全消除ThreadTerminateIfDone()。當FreeOnTerminate設置爲true，則線程被釋放之前OnTerminate被觸發，例如：

class TMyThread : public TThread 
{ 
private: 
    String StatusLine; // Used for Synchronize function 
    void __fastcall UpdateGUI(); 
protected: 
    virtual void __fastcall Execute(); 
public: 
    __fastcall TMyThread(); 
}; 
//------------------------------------------------------------------------------ 
extern TMyThread *MyThread; 
//------------------------------------------------------------------------------ 

。

TMyThread *MyThread = NULL; 

__fastcall TMyThread::TMyThread() 
    : TThread(true) 
{ 
    FreeOnTerminate = true; 
    Priority  = tpNormal; 
} 

void __fastcall TMyThread::UpdateGUI() 
{ 
    Form1->Label1 = StatusLine; 
} 

void __fastcall TMyThread::Execute() 
{ 
    Sleep(2000); 
    StatusLine = "I am almost done!"; 
    Synchronize(&UpdateGUI); 
} 

void __fastcall TForm1::StartOrRestartThread(TObject *Sender) 
{ 
    if (MyThread == NULL) 
    { 
     MyThread = new TMyThread(); 
     MyThread->OnTerminate = ThreadTerminated; 
     MyThread->Start(); 
    } 
    else 
    { 
     Application->MessageBox(L"Thread is still running please wait!", L"Error", MB_OK); 
    } 
} 

void __fastcall TForm1::ThreadTerminated(TObject *Sender) 
{ 
    MyThread = NULL; 
} 

爲了回答您的其他問題，如果你想線程可以重啓，那麼你必須改變線程設計了一下，如：

class TMyThread : public TThread 
{ 
private: 
    String StatusLine; // Used for Synchronize function 
    TEvent *RestartEvent; 
    void __fastcall UpdateGUI(); 
protected: 
    virtual void __fastcall Execute(); 
public: 
    bool Busy; 
    __fastcall TMyThread(); 
    __fastcall ~TMyThread(); 
    void __fastcall Restart(); 
}; 
//------------------------------------------------------------------------------ 
extern TMyThread *MyThread; 
//------------------------------------------------------------------------------ 

。

TMyThread *MyThread = NULL; 

__fastcall TMyThread::TMyThread() 
    : TThread(true) 
{ 
    FreeOnTerminate = true; 
    Priority  = tpNormal; 
    RestartEvent = new TEvent(nil, true, true, ""); 
} 

__fastcall TMyThread::~TMyThread() 
{ 
    delete RestartEvent; 
} 

void __fastcall TMyThread::UpdateGUI() 
{ 
    Form1->Label1 = StatusLine; 
} 

void __fastcall TMyThread::Execute() 
{ 
    while (!Terminated) 
    { 
     if (RestartEvent.WaitFor(1000) == wrSignaled) 
     { 
      if (Terminated) return; 

      RestartEvent.ResetEvent(); 
      Busy = true; 

      StatusLine = "I am doing something!"; 
      Synchronize(&UpdateGUI); 

      Sleep(2000); 

      StatusLine = "I am almost done!"; 
      Synchronize(&UpdateGUI); 

      Busy = false; 
     } 
    } 
} 

void __fastcall TForm1::StartOrRestartThread(TObject *Sender) 
{ 
    if (MyThread == NULL) 
    { 
     MyThread = new TMyThread(); 
     MyThread->OnTerminate = ThreadTerminated; 
     MyThread->Start(); 
    } 
    else if (!MyThread->Busy) 
    { 
     MyThread->Restart(); 
    } 
    else 
    { 
     Application->MessageBox(L"Thread is still running please wait!", L"Error", MB_OK); 
    } 
} 

void __fastcall TForm1::ThreadTerminated(TObject *Sender) 
{ 
    MyThread = NULL; 
} 

Answer 2

在頂端運行在線程while循環，用一些等待以允許其運行一次輪用信號時，是這樣優選的以持續創建/終止/銷燬線程，以及相關的微觀管理，即沒有其他課程是理智的。

創建線程，放在一個while循環中，在頂部等待，發出信號運行，永遠不會終止線程，除非絕對強制。死亡的

電話：

TThread.WaitFor 
TThread.Synchronize 
TThread.Terminate 

非常努力地不使用這些，永遠。

簡單的例子：

TmyThread=class(TThread); 
private; 
    mySimpleEvent:TSimpleEvent; 
public 
    constructor create; 
    procedure go; 
end; 

constructor TmyThread.create; 
begin 
    inherited create(true); 
    mySimpleEvent:=TSimpleEvent.Create; 
    resume; 
end; 

procedure TmyThread.go; 
begin 
    mySimpleEvent.SetEvent; 
end; 

procedure TmyThread.Execute; 
begin 
    while mySimpleEvent.WaitFor(INFINITE) do 
    begin 
    mySimpleEvent.ResetEvent; 
    //code to do your stuff 
    end; 
end;