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()

using namespace 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。