关于_endthread()后函数栈的析构

[飞翔的土豆]

MSDN上说：
“however, _endthread or _endthreadex is called automatically when the thread returns from the routine passed as a parameter to _beginthread or _beginthreadex. Terminating a thread with a call to endthread or _endthreadex helps to ensure proper recovery of resources allocated for the thread.”

那么如果我显式调用了_endthread后，当前函数还能否返回时正常析构吗？貌似_endthread后面的语句都不执行了~~
求高人解释，最好能给出线程主动退出时的一般做法~

[wy2001wy]

函数怎么会有析构？
MSDN上说是是MFC里面分配的一些东西会被正常的释放，跟你自己的东西没有关系的。

[WizardK]

线程主动退出（起始最终还是被动）做法的一种：
要求线程退出时，SetEvent

HANDLE g_hEvent;

UINT THREADFUNC(...)
{
  ...

  while (1)
  {
    if (WaitForSingleObject(g_hEvent, 0) == WAIT_OBJECT_0)
      break;
    ...
  }

  return 0;
}

[飞翔的土豆]

引用 1 楼 wy2001wy 的回复:

函数怎么会有析构？
MSDN上说是是MFC里面分配的一些东西会被正常的释放，跟你自己的东西没有关系的。

函数在退出时，不是会对函数栈里的对象依次析构吗？我的意思是，如果在线程函数里显示调用_endthread，那么函数还会继续走下去吗（如果_endthread后面还有别的代码的话）？甚至能否return呢？

[WizardK]

首先，_endthread和_beginthread配对使用
其次，能在线程内部调用_endthread，其后可以return。

看MSDN的例子：

// crt_BEGTHRD.C
// compile with: /MT /D "_X86_" /c
#include <windows.h>
#include <process.h>    /* _beginthread, _endthread */
#include <stddef.h>
#include <stdlib.h>
#include <conio.h>

void Bounce( void *ch );
void CheckKey( void *dummy );

/* GetRandom returns a random integer between min and max. */
#define GetRandom( min, max ) ((rand() % (int)(((max) + 1) - (min))) + (min))

BOOL repeat = TRUE;     /* Global repeat flag and video variable */
HANDLE hStdOut;         /* Handle for console window */
CONSOLE_SCREEN_BUFFER_INFO csbi;    /* Console information structure */

int main()
{
    CHAR    ch = 'A';

    hStdOut = GetStdHandle( STD_OUTPUT_HANDLE );

    /* Get display screen's text row and column information. */
   GetConsoleScreenBufferInfo( hStdOut, &csbi );

    /* Launch CheckKey thread to check for terminating keystroke. */
    _beginthread( CheckKey, 0, NULL );

    /* Loop until CheckKey terminates program. */
    while( repeat )
    {
        /* On first loops, launch character threads. */
        _beginthread( Bounce, 0, (void *) (ch++)  );

        /* Wait one second between loops. */
        Sleep( 1000L );
    }
}

/* CheckKey - Thread to wait for a keystroke, then clear repeat flag. */
void CheckKey( void *dummy )
{
    _getch();
    repeat = 0;    /* _endthread implied */

}

/* Bounce - Thread to create and and control a colored letter that moves
 * around on the screen.
 *
 * Params: ch - the letter to be moved
 */
void Bounce( void *ch )
{
    /* Generate letter and color attribute from thread argument. */
    char    blankcell = 0x20;
    char    blockcell = (char) ch;
    BOOL    first = TRUE;
   COORD   oldcoord, newcoord;
   DWORD   result;


    /* Seed random number generator and get initial location. */
    srand( _threadid );
    newcoord.X = GetRandom( 0, csbi.dwSize.X - 1 );
    newcoord.Y = GetRandom( 0, csbi.dwSize.Y - 1 );
    while( repeat )
    {
        /* Pause between loops. */
        Sleep( 100L );

        /* Blank out our old position on the screen, and draw new letter. */
        if( first )
            first = FALSE;
        else
         WriteConsoleOutputCharacter( hStdOut, &blankcell, 1, oldcoord, &result );
         WriteConsoleOutputCharacter( hStdOut, &blockcell, 1, newcoord, &result );

        /* Increment the coordinate for next placement of the block. */
        oldcoord.X = newcoord.X;
        oldcoord.Y = newcoord.Y;
        newcoord.X += GetRandom( -1, 1 );
        newcoord.Y += GetRandom( -1, 1 );

        /* Correct placement (and beep) if about to go off the screen. */
        if( newcoord.X < 0 )
            newcoord.X = 1;
        else if( newcoord.X == csbi.dwSize.X )
            newcoord.X = csbi.dwSize.X - 2;
        else if( newcoord.Y < 0 )
            newcoord.Y = 1;
        else if( newcoord.Y == csbi.dwSize.Y )
            newcoord.Y = csbi.dwSize.Y - 2;

        /* If not at a screen border, continue, otherwise beep. */
        else
            continue;
        Beep( ((char) ch - 'A') * 100, 175 );
    }
    /* _endthread given to terminate */
    _endthread();
}

[WizardK]

另一个_endthreadex和_beginthreadex的例子：
这个和_endthread的区别是需要你自己去关闭线程句柄，和ExitThread一样。

// crt_begthrdex.cpp
// compile with: /MT
#include <windows.h>
#include <stdio.h>
#include <process.h>

unsigned Counter; 
unsigned __stdcall SecondThreadFunc( void* pArguments )
{
    printf( "In second thread...\n" );

    while ( Counter < 1000000 )
        Counter++;

    _endthreadex( 0 );
    return 0;
} 

int main()
{ 
    HANDLE hThread;
    unsigned threadID;

    printf( "Creating second thread...\n" );

    // Create the second thread.
    hThread = (HANDLE)_beginthreadex( NULL, 0, &SecondThreadFunc, NULL, 0, &threadID );

    // Wait until second thread terminates. If you comment out the line
    // below, Counter will not be correct because the thread has not
    // terminated, and Counter most likely has not been incremented to
    // 1000000 yet.
    WaitForSingleObject( hThread, INFINITE );
    printf( "Counter should be 1000000; it is-> %d\n", Counter );
    // Destroy the thread object.
    CloseHandle( hThread );
}

[飞翔的土豆]

事实证明：函数栈回收时不析构。。简单写了个程序如下：

#include <Windows.h>
#include <process.h>
#include <iostream>
#include <list>
using namespace std;

class CMyClass
{
public:
	CMyClass()
	{
		cout<<"Default constructor"<<endl;
	}
	CMyClass(const CMyClass& obj)
	{
		cout<<"Copy constructor"<<endl;
	}
	~CMyClass()
	{
		cout<<"Destructor"<<endl;
	}
};
void ThreadFunc(LPVOID lParam)
{
	CMyClass myobj;
//	_endthread();
}
void main()
{
	_beginthread(ThreadFunc,0,NULL);
	char c;
	cin>>c;
}

注释如果去掉的话，自定义的myobj没能析构。。

[stjay]

_endthread后线程都终结了,后面的语句就不会执行了
最好的线程主动退出时的一般做法 就是直接return;

#include <Windows.h>
#include <process.h>
#include <iostream>
#include <list>
using namespace std;

class CMyClass
{
public:
    CMyClass()
    {
        cout<<"Default constructor"<<endl;
    }
    CMyClass(const CMyClass& obj)
    {
        cout<<"Copy constructor"<<endl;
    }
    ~CMyClass()
    {
        cout<<"Destructor"<<endl;
    }
};
void ThreadFunc(LPVOID lParam)
{
    if(lParam==NULL)
    {
       return;
    }
    CMyClass myobj;
//    _endthread();
}
void main()
{
    _beginthread(ThreadFunc,0,NULL);
    char c;
    cin>>c;
}