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MFC全局函數(shù)::AfxBeginThread

CWinThread* AfxBeginThread(
   CRuntimeClass* pThreadClass,
   int nPriority = THREAD_PRIORITY_NORMAL,
   UINT nStackSize = 0,
   DWORD dwCreateFlags = 0,
   LPSECURITY_ATTRIBUTES lpSecurityAttrs = NULL 
);

參數(shù)說明:
pfnThreadProc:線程函數(shù)的地址,該參數(shù)不能設(shè)置為NULL,線程函數(shù)必須定義成全局函數(shù)或者類的靜態(tài)成員函數(shù)
例如:
UINT myThreadFunc(LPVOID lparam)
或者
class A
{
public:
        static UINT __stdcall myThreadFunc(LPVOID lparam);
}
之所以要定義成類的靜態(tài)成員函數(shù),是因?yàn)轭惖撵o態(tài)成員函數(shù)不屬于某個(gè)類對(duì)象,這樣在調(diào)用函數(shù)
的時(shí)候就不用傳遞一個(gè)額外的this指針.

pThreadClass:指向從CWinThread派生的子類對(duì)象的RUNTIME_CLASS

pParam:要傳遞給線程函數(shù)的參數(shù)

nPriority:要啟動(dòng)的線程的優(yōu)先級(jí),默認(rèn)優(yōu)先級(jí)為THREAD_PRIORITY_NORMAL(普通優(yōu)先級(jí)),關(guān)于線程
 優(yōu)先級(jí)的詳細(xì)說明請(qǐng)參考Platform SDK SetThreadPriority函數(shù)說明

nStackSize:新線程的堆棧大小,如果設(shè)置為0,則使用默認(rèn)大小,在應(yīng)用程序中一般情況下線程的默認(rèn)堆棧大小
 為1M

dwCreateFlags:線程創(chuàng)建標(biāo)志,該參數(shù)可以指定為下列標(biāo)志
 CREATE_SUSPENDED:以掛起方式啟動(dòng)線程,如果你在線程啟動(dòng)之前想初始化一些CWinThread類中的一些成員變量
 比如:m_bAutoDelete或者你的派生類中的成員變量,當(dāng)初始化完成之后,你可以使用CWinThread類的ResumeThread
 成員函數(shù)來恢復(fù)線程的運(yùn)行
 如果把該標(biāo)志設(shè)置為0,則表示立即啟動(dòng)線程
lpSecurityAttrs:指向安全描述符的指針,如果使用默認(rèn)的安全級(jí)別只要講該參數(shù)設(shè)置為NULL就可以了!

上面就是AfxBeginThread函數(shù)的簡單說明,我們?cè)谑褂玫臅r(shí)候一般情況下只要指定前兩個(gè)參數(shù),其他
參數(shù)使用默認(rèn)值就可以.嗯,的確,使用起來是很簡單,只要這個(gè)函數(shù)一被調(diào)用,就創(chuàng)建了一個(gè)線程.
但是大家有沒有想過,AfxBeginThread函數(shù)究竟是如何啟動(dòng)的線程呢?它的內(nèi)部是如何實(shí)現(xiàn)的呢?

下面我們就來看一下AfxBeginThread函數(shù)的內(nèi)部實(shí)現(xiàn)

//啟動(dòng)worker線程
CWinThread* AFXAPI AfxBeginThread(AFX_THREADPROC pfnThreadProc, LPVOID pParam,
 int nPriority, UINT nStackSize, DWORD dwCreateFlags,
 LPSECURITY_ATTRIBUTES lpSecurityAttrs)
{
#ifndef _MT
         pfnThreadProc;
         pParam;
         nPriority;
         nStackSize;
         dwCreateFlags;
         lpSecurityAttrs;

         return NULL;
#else
         ASSERT(pfnThreadProc != NULL);

         CWinThread* pThread = DEBUG_NEW CWinThread(pfnThreadProc, pParam);
         ASSERT_VALID(pThread);

         if (!pThread->CreateThread(dwCreateFlags|CREATE_SUSPENDED, nStackSize,
                  lpSecurityAttrs))
         {
                  pThread->Delete();
                  return NULL;
         }
         VERIFY(pThread->SetThreadPriority(nPriority));
         if (!(dwCreateFlags & CREATE_SUSPENDED))
                  VERIFY(pThread->ResumeThread() != (DWORD)-1);

         return pThread;
#endif //!_MT)
}

//啟動(dòng)UI線程
CWinThread* AFXAPI AfxBeginThread(CRuntimeClass* pThreadClass,
 int nPriority, UINT nStackSize, DWORD dwCreateFlags,
 LPSECURITY_ATTRIBUTES lpSecurityAttrs)
{
#ifndef _MT
        pThreadClass;
        nPriority;
        nStackSize;
        dwCreateFlags;
        lpSecurityAttrs;

        return NULL;
#else
        ASSERT(pThreadClass != NULL);
        ASSERT(pThreadClass->IsDerivedFrom(RUNTIME_CLASS(CWinThread)));

        CWinThread* pThread = (CWinThread*)pThreadClass->CreateObject();
        if (pThread == NULL)
                AfxThrowMemoryException();
        ASSERT_VALID(pThread);

        pThread->m_pThreadParams = NULL;
        if (!pThread->CreateThread(dwCreateFlags|CREATE_SUSPENDED, nStackSize,
                lpSecurityAttrs))
        {
                pThread->Delete();
                return NULL;
        }
        VERIFY(pThread->SetThreadPriority(nPriority));
        if (!(dwCreateFlags & CREATE_SUSPENDED))
                VERIFY(pThread->ResumeThread() != (DWORD)-1);

        return pThread;
#endif //!_MT
}

從上面的代碼中可以看出AfxBeginThread所做的事情主要有以下幾點(diǎn):

1.在heap中配置一個(gè)新的CWinThread對(duì)象(worker線程)
代碼如:CWinThread* pThread = DEBUG_NEW CWinThread(pfnThreadProc, pParam);
調(diào)用CRuntimeClass結(jié)構(gòu)中的CreateObject函數(shù)創(chuàng)建CWinThread對(duì)象
CWinThread* pThread = (CWinThread*)pThreadClass->CreateObject();
CRuntimeClass以及MFC相關(guān)類的內(nèi)部實(shí)現(xiàn),詳情請(qǐng)參考
《深入淺出MFC》侯捷著

2.調(diào)用CWinThread::CreateThread()并設(shè)定屬性,使線程以掛起狀態(tài)產(chǎn)生
pThread->CreateThread(dwCreateFlags|CREATE_SUSPENDED, nStackSize,lpSecurityAttrs);

3.設(shè)定線程的優(yōu)先權(quán)
pThread->SetThreadPriority(nPriority);

4.調(diào)用CWinThread::ResumeThread
pThread->ResumeThread();

通過上面的說明,我想大家對(duì)該函數(shù)到底在內(nèi)部都做了什么,應(yīng)該有一個(gè)初步的了解了!