C++多线程实例(_beginThreadex创建多线程)

C++多线程（二）(_beginThreadex创建多线程) 

C/C++ Runtime 多线程函数

一 简单实例（来自codeprojct：http://www.codeproject.com/useritems/MultithreadingTutorial.asp）
主线程创建2个线程t1和t2，创建时2个线程就被挂起，后来调用ResumeThread恢复2个线程，是其开始执行，调用WaitForSingleObject等待2个线程执行完，然后推出主线程即结束进程。

/*  file Main.cpp
*
*  This program is an adaptation of the code Rex Jaeschke showed in
*  Listing 1 of his Oct 2005 C/C++ User's Journal article entitled
*  "C++/CLI Threading: Part I".  I changed it from C++/CLI (managed)
*  code to standard C++.
*
*  One hassle is the fact that C++ must employ a free (C) function
*  or a static class member function as the thread entry function.
*
*  This program must be compiled with a multi-threaded C run-time
*  (/MT for LIBCMT.LIB in a release build or /MTd for LIBCMTD.LIB
*  in a debug build).
*
*                                      John Kopplin  7/2006
*/


#include<stdio.h>
#include<string>            // for STL string class
#include<windows.h>         // for HANDLE
#include<process.h>         // for _beginthread()

usingnamespace std;


class ThreadX
{
private:
 int loopStart;
 int loopEnd;
 int dispFrequency;

public:
 string threadName;

  ThreadX(int startValue,int endValue,int frequency )
 {
    loopStart= startValue;
    loopEnd= endValue;
    dispFrequency= frequency;
  }

 // In C++ you must employ a free (C) function or a static
 // class member function as the thread entry-point-function.
 // Furthermore, _beginthreadex() demands that the thread
 // entry function signature take a single (void*) and returned
 // an unsigned.
 static unsigned __stdcall ThreadStaticEntryPoint(void* pThis)
 {
      ThreadX* pthX = (ThreadX*)pThis;  // the tricky cast
      pthX->ThreadEntryPoint();          // now call the true entry-point-function

     // A thread terminates automatically if it completes execution,
     // or it can terminate itself with a call to _endthread().

     return 1;          // the thread exit code
  }

 void ThreadEntryPoint()
 {
    // This is the desired entry-point-function but to get
    // here we have to use a 2 step procedure involving
    // the ThreadStaticEntryPoint() function.

   for (int i= loopStart; i<= loopEnd;++i)
   {
     if (i % dispFrequency == 0)
     {
          printf("%s: i = %d\n", threadName.c_str(), i );
      }
    }
    printf("%s thread terminating\n", threadName.c_str() );
  }
};


int main()
{
   // All processes get a primary thread automatically. This primary
   // thread can generate additional threads.  In this program the
   // primary thread creates 2 additional threads and all 3 threads
   // then run simultaneously without any synchronization.  No data
   // is shared between the threads.

   // We instantiate an object of the ThreadX class. Next we will
   // create a thread and specify that the thread is to begin executing
   // the function ThreadEntryPoint() on object o1. Once started,
   // this thread will execute until that function terminates or
   // until the overall process terminates.

    ThreadX* o1 = new ThreadX(0, 1,2000 );

   // When developing a multithreaded WIN32-based application with
   // Visual C++, you need to use the CRT thread functions to create
   // any threads that call CRT functions. Hence to create and terminate
   // threads, use _beginthreadex() and _endthreadex() instead of
   // the Win32 APIs CreateThread() and EndThread().

   // The multithread library LIBCMT.LIB includes the _beginthread()
   // and _endthread() functions. The _beginthread() function performs
   // initialization without which many C run-time functions will fail.
   // You must use _beginthread() instead of CreateThread() in C programs
   // built with LIBCMT.LIB if you intend to call C run-time functions.

   // Unlike the thread handle returned by _beginthread(), the thread handle
   // returned by _beginthreadex() can be used with the synchronization APIs.

    HANDLE   hth1;
    unsigned  uiThread1ID;

    hth1= (HANDLE)_beginthreadex( NULL,        // security
                                  0,           // stack size
                                   ThreadX::ThreadStaticEntryPoint,
                                   o1,          // arg list
                                  CREATE_SUSPENDED,  // so we can later call ResumeThread()
                                  &uiThread1ID );

   if ( hth1 == 0 )
        printf("Failed to create thread 1\n");

    DWORD   dwExitCode;

  GetExitCodeThread( hth1, &dwExitCode ); // should be STILL_ACTIVE = 0x00000103 = 259
    printf("initial thread 1 exit code = %u\n", dwExitCode );

   // The System::Threading::Thread object in C++/CLI has a "Name" property.
   // To create the equivalent functionality in C++ I added a public data member
   // named threadName.

    o1->threadName= "t1";

    ThreadX* o2 = new ThreadX(-1000000,0, 2000 );

    HANDLE  hth2;
    unsigned  uiThread2ID;

    hth2= (HANDLE)_beginthreadex( NULL,        // security
                                  0,           // stack size
                                   ThreadX::ThreadStaticEntryPoint,
                                   o2,          // arg list
                                   CREATE_SUSPENDED, // so we can later call ResumeThread()
                                  &uiThread2ID );

   if ( hth2 == 0 )
        printf("Failed to create thread 2\n");

   GetExitCodeThread( hth2, &dwExitCode ); // should be STILL_ACTIVE = 0x00000103 = 259
    printf("initial thread 2 exit code = %u\n", dwExitCode );

    o2->threadName= "t2";

   // If we hadn't specified CREATE_SUSPENDED in the call to _beginthreadex()
   // we wouldn't now need to call ResumeThread().

  ResumeThread( hth1 );   // serves the purpose of Jaeschke's t1->Start()

   ResumeThread( hth2 );//你需要恢复线程的句柄 使用该函数能够激活线程的运行

   // In C++/CLI the process continues until the last thread exits.
   // That is, the thread's have independent lifetimes. Hence
   // Jaeschke's original code was designed to show that the primary
   // thread could exit and not influence the other threads.

   // However in C++ the process terminates when the primary thread exits
   // and when the process terminates all its threads are then terminated.
   // Hence if you comment out the following waits, the non-primary
   // threads will never get a chance to run.

   WaitForSingleObject( hth1, INFINITE );
   WaitForSingleObject( hth2, INFINITE );
          //WaitForSingleObject函数用来检测hHandle事件的信号状态，当函数的执行时间超过dwMilliseconds就返回，
     //但如果参数 dwMilliseconds为INFINITE时函数将直到相应时间事件变成有信号状态才返回，否则就一直等待下去
     //，直到 WaitForSingleObject有返回直才执行后面的代码

   GetExitCodeThread( hth1, &dwExitCode );
    printf("thread 1 exited with code %u\n", dwExitCode );

   GetExitCodeThread( hth2, &dwExitCode );
    printf("thread 2 exited with code %u\n", dwExitCode );
         //

//GetExitCodeThread这个函数是获得线程的退出码，  第二个参数是一个 DWORD的指针，//用户应该使用一个 DWORD 类型的变量去接收数据，返回的数据是线程的退出码，//第一个参数是线程句柄，用 CreateThread 创建线程时获得到。//通过线程退出码可以判断线程是否正在运行，还是已经退出。

   // The handle returned by _beginthreadex() has to be closed
   // by the caller of _beginthreadex().

   CloseHandle( hth1 );
   CloseHandle( hth2 );

    delete o1;
    o1= NULL;

    delete o2;
    o2= NULL;

    printf("Primary thread terminating.\n");
}

二解释
1）如果你正在编写C/C++代码，决不应该调用CreateThread。相反，应该使用VisualC++运行期库函数_beginthreadex，推出也应该使用_endthreadex。如果不使用Microsoft的VisualC++编译器，你的编译器供应商有它自己的CreateThred替代函数。不管这个替代函数是什么，你都必须使用。

2）因为_beginthreadex和_endthreadex是CRT线程函数，所以必须注意编译选项runtimelibaray的选择，使用MT或MTD。

3) _beginthreadex函数的参数列表与CreateThread函数的参数列表是相同的，但是参数名和类型并不完全相同。这是因为Microsoft的C/C++运行期库的开发小组认为，C/C++运行期函数不应该对Windows数据类型有任何依赖。_beginthreadex函数也像CreateThread那样，返回新创建的线程的句柄。
下面是关于_beginthreadex的一些要点：
&8226;每个线程均获得由C/C++运行期库的堆栈分配的自己的tiddata内存结构。（tiddata结构位于Mtdll.h文件中的VisualC++源代码中）。

&8226;传递给_beginthreadex的线程函数的地址保存在tiddata内存块中。传递给该函数的参数也保存在该数据块中。

&8226;_beginthreadex确实从内部调用CreateThread，因为这是操作系统了解如何创建新线程的唯一方法。

&8226;当调用CreatetThread时，它被告知通过调用_threadstartex而不是pfnStartAddr来启动执行新线程。还有，传递给线程函数的参数是tiddata结构而不是pvParam的地址。

&8226;如果一切顺利，就会像CreateThread那样返回线程句柄。如果任何操作失败了，便返回NULL。

4) _endthreadex的一些要点：
&8226;C运行期库的_getptd函数内部调用操作系统的TlsGetValue函数，该函数负责检索调用线程的tiddata内存块的地址。

&8226;然后该数据块被释放，而操作系统的ExitThread函数被调用，以便真正撤消该线程。当然，退出代码要正确地设置和传递。

5)虽然也提供了简化版的的_beginthread和_endthread，但是可控制性太差，所以一般不使用。

6）线程handle因为是内核对象，所以需要在最后closehandle。

7）更多的API：

HANDLE GetCurrentProcess();

HANDLE GetCurrentThread();

DWORD GetCurrentProcessId();

DWORD GetCurrentThreadId()。

DWORD SetThreadIdealProcessor(HANDLE hThread,DWORD dwIdealProcessor);

BOOL SetThreadPriority(HANDLE hThread,int nPriority);

BOOL SetPriorityClass(GetCurrentProcess(),  IDLE_PRIORITY_CLASS);

BOOL GetThreadContext(HANDLE hThread,PCONTEXT pContext);BOOL SwitchToThread();

三注意
1）C++主线程的终止，同时也会终止所有主线程创建的子线程，不管子线程有没有执行完毕。所以上面的代码中如果不调用WaitForSingleObject，则2个子线程t1和t2可能并没有执行完毕或根本没有执行。
2）如果某线程挂起，然后有调用WaitForSingleObject等待该线程，就会导致死锁。所以上面的代码如果不调用resumethread，则会死锁。

为什么要用C运行时库的_beginthreadex代替操作系统的CreateThread来创建线程？

来源自自1999年7月MSJ杂志的《Win32 Q&A》栏目

你也许会说我一直用CreateThread来创建线程，一直都工作得好好的，为什么要用_beginthreadex来代替CreateThread，下面让我来告诉你为什么。
回答一个问题可以有两种方式，一种是简单的，一种是复杂的。
如果你不愿意看下面的长篇大论，那我可以告诉你简单的答案：_beginthreadex在内部调用了CreateThread，在调用之前_beginthreadex做了很多的工作，从而使得它比CreateThread更安全。