终止线程变量，并将其设置为NULL

Question

当TThread后代的工作我基本上有一个选择：

• 设置FreeOnTerminate到true它删除我的TThread后代对象，但不会将其设置为NULL
• 做手动，并通过自己删除它的所有烂摊子

我基本上需要的是一种方式来确定线程是否正在运行，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); 
    } 
} 

此代码按原样运行。我的问题是：

• 有没有办法简化这个？我需要在完成后将MyThread设置为NULL，以便在下次调用启动/重新启动之前，对象不在周围。这不能用FreeOnTerminate设置为true来完成，因为它会删除对象。我只能尝试访问对象，然后生成异常（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启动MyThread之前是否执行了执行。

• 我可以重新启动线程而不终止它（我不需要在程序结束之前删除对象） - 如果我启动线程，我会得到“无法在运行或挂起的线程上调用启动”异常。

Answer 1

你ThreadTerminateIfDone()功能需要通过参考拿线程指针，否则将无法设置指向正确NULL：

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

随着中说，如果使用线程的OnTerminate事件来跟踪线程是否正在运行，则可以完全消除ThreadTerminateIfDone()。当FreeOnTerminate设置为true，则线程被释放之前OnTerminate被触发，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; 
} 

为了回答您的其他问题，如果你想线程可以重启，那么你必须改变线程设计了一下，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

在顶端运行在线程while循环，用一些等待以允许其运行一次轮用信号时，是这样优选的以持续创建/终止/销毁线程，以及相关的微观管理，即没有其他课程是理智的。

创建线程，放在一个while循环中，在顶部等待，发出信号运行，永远不会终止线程，除非绝对强制。死亡的

电话：

TThread.WaitFor 
TThread.Synchronize 
TThread.Terminate 

非常努力地不使用这些，永远。

简单的例子：

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;