AfxBeginThread和AfxEndThread及线程资源分配和释放

 AfxBeginThread动态创建CWinThread(或派生类)线程对象,并分配相关资源.

AfxEndThread会释放线程资源和CWinThread(或派生类)线程对象.

下面这个过程的分析,这里仅仅给出简单代码用于说明问题.

首先看一下创建线程的函数.

 

CWinThread* AFXAPI AfxBeginThread(CRuntimeClass* pThreadClass,
    int nPriority, UINT nStackSize, DWORD dwCreateFlags,
    LPSECURITY_ATTRIBUTES lpSecurityAttrs)
{
  ......

    // 创建线程对象.CreateObject()函数内部有new操作符.
    CWinThread* pThread = (CWinThread*)pThreadClass->CreateObject();

    // 创建线程.
    pThread->m_pThreadParams = NULL;
    pThread->CreateThread(dwCreateFlags|CREATE_SUSPENDED, nStackSize, lpSecurityAttrs)

    return pThread;
}

注意红色的文字,CreateObject()函数内适用new操作符创建线程对象CWinThread或者其派生类对象.

 

下面是CreateThread函数.

 

BOOL CWinThread::CreateThread(DWORD dwCreateFlags, UINT nStackSize,
    LPSECURITY_ATTRIBUTES lpSecurityAttrs)
{
    ... ...
    // create the thread (it may or may not start to run)
    m_hThread = (HANDLE)(ULONG_PTR)_beginthreadex(lpSecurityAttrs, nStackSize,
    &_AfxThreadEntry, &startup, dwCreateFlags | CREATE_SUSPENDED, (UINT*)&m_nThreadID);
    ... ...
    return TRUE;
}

这个函数调用_beginthreadex创建线程.

注意线程回调函数_AfxThreadEntry,下面是其部分代码.

UINT APIENTRY _AfxThreadEntry(void* pParam)
{
    _AFX_THREAD_STARTUP* pStartup = (_AFX_THREAD_STARTUP*)pParam;

    CWinThread* pThread = pStartup->pThread;

    ... ...
    // forced initialization of the thread
    AfxInitThread();

  ... ...

    AfxEndThread(nResult);

    return 0;   // not reached
}

这个函数调用了函数AfxEndThread().从这里可以看出,若CWinThread(获取派生类)对象如果能够从线程函数正常返回,一定会调用AfxEndThread()函数. 

下面是AfxEndThread函数的代码.

 

void AFXAPI AfxEndThread(UINT nExitCode, BOOL bDelete)
{
    ... ...
    pThread->Delete();

    // allow cleanup of any thread local objects
    AfxTermThread();

    // allow C-runtime to cleanup, and exit the thread
    _endthreadex(nExitCode);
}

void CWinThread::Delete()
{
    // delete thread if it is auto-deleting
    if (m_bAutoDelete)
        delete this;
}

从注释和代码可以看出,该函数用来释放资源和CWinThread对象(delete this).

 

从上面的分析可以看出, 函数调用AfxBeginThread可以动态创建CWinThread(或派生类)对象,如果能够保证程序正常从线程回调函数退出(也就是CWinThread::Run()函数),就能够保证线程对象及资源被正确释放.