C++多线程（二）

悠悠 2022-08-14 00:43 240阅读 0赞

C/C++ Runtime 多线程函数  
  
一 简单实例（来自codeprojct：[http://www.codeproject.com/useritems/MultithreadingTutorial.asp][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。

![ExpandedBlockStart.gif][]/\*  file Main.cpp  
![InBlock.gif][] \*  
![InBlock.gif][] \*  This program is an adaptation of the code Rex Jaeschke showed in  
![InBlock.gif][] \*  Listing 1 of his Oct 2005 C/C++ User's Journal article entitled  
![InBlock.gif][] \*  "C++/CLI Threading: Part I".  I changed it from C++/CLI (managed)  
![InBlock.gif][] \*  code to standard C++.  
![InBlock.gif][] \*  
![InBlock.gif][] \*  One hassle is the fact that C++ must employ a free (C) function  
![InBlock.gif][] \*  or a static class member function as the thread entry function.  
![InBlock.gif][] \*  
![InBlock.gif][] \*  This program must be compiled with a multi-threaded C run-time  
![InBlock.gif][] \*  (/MT for LIBCMT.LIB in a release build or /MTd for LIBCMTD.LIB  
![InBlock.gif][] \*  in a debug build).  
![InBlock.gif][] \*  
![InBlock.gif][] \*                                      John Kopplin  7/2006  
![ExpandedBlockEnd.gif][] \*/  
![None.gif][]  
![None.gif][]  
![None.gif][]\#include <stdio.h>  
![None.gif][]\#include <string>             // for STL string class  
![None.gif][]\#include <windows.h>          // for HANDLE  
![None.gif][]\#include <process.h>          // for \_beginthread()  
![None.gif][]  
![None.gif][]using namespace std;  
![None.gif][]  
![None.gif][]  
![None.gif][]class ThreadX  
![ExpandedBlockStart.gif][]\{  
![InBlock.gif][]private:  
![InBlock.gif][]  int loopStart;  
![InBlock.gif][]  int loopEnd;  
![InBlock.gif][]  int dispFrequency;  
![InBlock.gif][]  
![InBlock.gif][]public:  
![InBlock.gif][]  string threadName;  
![InBlock.gif][]  
![InBlock.gif][]  ThreadX( int startValue, int endValue, int frequency )  
![ExpandedSubBlockStart.gif][]  \{  
![InBlock.gif][]    loopStart = startValue;  
![InBlock.gif][]    loopEnd = endValue;  
![InBlock.gif][]    dispFrequency = frequency;  
![ExpandedSubBlockEnd.gif][]  \}  
![InBlock.gif][]  
![InBlock.gif][]  // In C++ you must employ a free (C) function or a static  
![InBlock.gif][]  // class member function as the thread entry-point-function.  
![InBlock.gif][]  // Furthermore, \_beginthreadex() demands that the thread  
![InBlock.gif][]  // entry function signature take a single (void\*) and returned  
![InBlock.gif][]  // an unsigned.  
![InBlock.gif][]  static unsigned \_\_stdcall ThreadStaticEntryPoint(void \* pThis)  
![ExpandedSubBlockStart.gif][]  \{  
![InBlock.gif][]      ThreadX \* pthX = (ThreadX\*)pThis;   // the tricky cast  
![InBlock.gif][]      pthX->ThreadEntryPoint();           // now call the true entry-point-function  
![InBlock.gif][]  
![InBlock.gif][]      // A thread terminates automatically if it completes execution,  
![InBlock.gif][]      // or it can terminate itself with a call to \_endthread().  
![InBlock.gif][]  
![InBlock.gif][]      return 1;          // the thread exit code  
![ExpandedSubBlockEnd.gif][]  \}  
![InBlock.gif][]  
![InBlock.gif][]  void ThreadEntryPoint()  
![ExpandedSubBlockStart.gif][]  \{  
![InBlock.gif][]     // This is the desired entry-point-function but to get  
![InBlock.gif][]     // here we have to use a 2 step procedure involving  
![InBlock.gif][]     // the ThreadStaticEntryPoint() function.  
![InBlock.gif][]  
![InBlock.gif][]    for (int i = loopStart; i <= loopEnd; ++i)  
![ExpandedSubBlockStart.gif][]    \{  
![InBlock.gif][]      if (i % dispFrequency == 0)  
![ExpandedSubBlockStart.gif][]      \{  
![InBlock.gif][]          printf( "%s: i = %d\\n", threadName.c\_str(), i );  
![ExpandedSubBlockEnd.gif][]      \}  
![ExpandedSubBlockEnd.gif][]    \}  
![InBlock.gif][]    printf( "%s thread terminating\\n", threadName.c\_str() );  
![ExpandedSubBlockEnd.gif][]  \}  
![ExpandedBlockEnd.gif][]\};  
![None.gif][]  
![None.gif][]  
![None.gif][]int main()  
![ExpandedBlockStart.gif][]\{  
![InBlock.gif][]    // All processes get a primary thread automatically. This primary  
![InBlock.gif][]    // thread can generate additional threads.  In this program the  
![InBlock.gif][]    // primary thread creates 2 additional threads and all 3 threads  
![InBlock.gif][]    // then run simultaneously without any synchronization.  No data  
![InBlock.gif][]    // is shared between the threads.  
![InBlock.gif][]  
![InBlock.gif][]    // We instantiate an object of the ThreadX class. Next we will  
![InBlock.gif][]    // create a thread and specify that the thread is to begin executing  
![InBlock.gif][]    // the function ThreadEntryPoint() on object o1. Once started,  
![InBlock.gif][]    // this thread will execute until that function terminates or  
![InBlock.gif][]    // until the overall process terminates.  
![InBlock.gif][]  
![InBlock.gif][]    ThreadX \* o1 = new ThreadX( 0, 1, 2000 );  
![InBlock.gif][]  
![InBlock.gif][]    // When developing a multithreaded WIN32-based application with  
![InBlock.gif][]    // Visual C++, you need to use the CRT thread functions to create  
![InBlock.gif][]    // any threads that call CRT functions. Hence to create and terminate  
![InBlock.gif][]    // threads, use \_beginthreadex() and \_endthreadex() instead of  
![InBlock.gif][]    // the Win32 APIs CreateThread() and EndThread().  
![InBlock.gif][]  
![InBlock.gif][]    // The multithread library LIBCMT.LIB includes the \_beginthread()  
![InBlock.gif][]    // and \_endthread() functions. The \_beginthread() function performs  
![InBlock.gif][]    // initialization without which many C run-time functions will fail.  
![InBlock.gif][]    // You must use \_beginthread() instead of CreateThread() in C programs  
![InBlock.gif][]    // built with LIBCMT.LIB if you intend to call C run-time functions.  
![InBlock.gif][]  
![InBlock.gif][]    // Unlike the thread handle returned by \_beginthread(), the thread handle  
![InBlock.gif][]    // returned by \_beginthreadex() can be used with the synchronization APIs.  
![InBlock.gif][]  
![InBlock.gif][]    HANDLE   hth1;  
![InBlock.gif][]    unsigned  uiThread1ID;  
![InBlock.gif][]  
![InBlock.gif][]    hth1 = (HANDLE)\_beginthreadex( NULL,         // security  
![InBlock.gif][]                                   0,            // stack size  
![InBlock.gif][]                                   ThreadX::ThreadStaticEntryPoint,  
![InBlock.gif][]                                   o1,           // arg list  
![InBlock.gif][]                                   CREATE\_SUSPENDED,  // so we can later call ResumeThread()  
![InBlock.gif][]                                   &uiThread1ID );  
![InBlock.gif][]  
![InBlock.gif][]    if ( hth1 == 0 )  
![InBlock.gif][]        printf("Failed to create thread 1\\n");  
![InBlock.gif][]  
![InBlock.gif][]    DWORD   dwExitCode;  
![InBlock.gif][]  
![InBlock.gif][]    GetExitCodeThread( hth1, &dwExitCode );  // should be STILL\_ACTIVE = 0x00000103 = 259  
![InBlock.gif][]    printf( "initial thread 1 exit code = %u\\n", dwExitCode );  
![InBlock.gif][]  
![InBlock.gif][]    // The System::Threading::Thread object in C++/CLI has a "Name" property.  
![InBlock.gif][]    // To create the equivalent functionality in C++ I added a public data member  
![InBlock.gif][]    // named threadName.  
![InBlock.gif][]  
![InBlock.gif][]    o1->threadName = "t1";  
![InBlock.gif][]  
![InBlock.gif][]    ThreadX \* o2 = new ThreadX( -1000000, 0, 2000 );  
![InBlock.gif][]  
![InBlock.gif][]    HANDLE   hth2;  
![InBlock.gif][]    unsigned  uiThread2ID;  
![InBlock.gif][]  
![InBlock.gif][]    hth2 = (HANDLE)\_beginthreadex( NULL,         // security  
![InBlock.gif][]                                   0,            // stack size  
![InBlock.gif][]                                   ThreadX::ThreadStaticEntryPoint,  
![InBlock.gif][]                                   o2,           // arg list  
![InBlock.gif][]                                   CREATE\_SUSPENDED,  // so we can later call ResumeThread()  
![InBlock.gif][]                                   &uiThread2ID );  
![InBlock.gif][]  
![InBlock.gif][]    if ( hth2 == 0 )  
![InBlock.gif][]        printf("Failed to create thread 2\\n");  
![InBlock.gif][]  
![InBlock.gif][]    GetExitCodeThread( hth2, &dwExitCode );  // should be STILL\_ACTIVE = 0x00000103 = 259  
![InBlock.gif][]    printf( "initial thread 2 exit code = %u\\n", dwExitCode );  
![InBlock.gif][]  
![InBlock.gif][]    o2->threadName = "t2";  
![InBlock.gif][]  
![InBlock.gif][]    // If we hadn't specified CREATE\_SUSPENDED in the call to \_beginthreadex()  
![InBlock.gif][]    // we wouldn't now need to call ResumeThread().  
![InBlock.gif][]  
![InBlock.gif][]    ResumeThread( hth1 );   // serves the purpose of Jaeschke's t1->Start()  
![InBlock.gif][]  
![InBlock.gif][]    ResumeThread( hth2 );  
![InBlock.gif][]  
![InBlock.gif][]    // In C++/CLI the process continues until the last thread exits.  
![InBlock.gif][]    // That is, the thread's have independent lifetimes. Hence  
![InBlock.gif][]    // Jaeschke's original code was designed to show that the primary  
![InBlock.gif][]    // thread could exit and not influence the other threads.  
![InBlock.gif][]  
![InBlock.gif][]    // However in C++ the process terminates when the primary thread exits  
![InBlock.gif][]    // and when the process terminates all its threads are then terminated.  
![InBlock.gif][]    // Hence if you comment out the following waits, the non-primary  
![InBlock.gif][]    // threads will never get a chance to run.  
![InBlock.gif][]  
![InBlock.gif][]    WaitForSingleObject( hth1, INFINITE );  
![InBlock.gif][]    WaitForSingleObject( hth2, INFINITE );  
![InBlock.gif][]  
![InBlock.gif][]    GetExitCodeThread( hth1, &dwExitCode );  
![InBlock.gif][]    printf( "thread 1 exited with code %u\\n", dwExitCode );  
![InBlock.gif][]  
![InBlock.gif][]    GetExitCodeThread( hth2, &dwExitCode );  
![InBlock.gif][]    printf( "thread 2 exited with code %u\\n", dwExitCode );  
![InBlock.gif][]  
![InBlock.gif][]    // The handle returned by \_beginthreadex() has to be closed  
![InBlock.gif][]    // by the caller of \_beginthreadex().  
![InBlock.gif][]  
![InBlock.gif][]    CloseHandle( hth1 );  
![InBlock.gif][]    CloseHandle( hth2 );  
![InBlock.gif][]  
![InBlock.gif][]    delete o1;  
![InBlock.gif][]    o1 = NULL;  
![InBlock.gif][]  
![InBlock.gif][]    delete o2;  
![InBlock.gif][]    o2 = NULL;  
![InBlock.gif][]  
![InBlock.gif][]    printf("Primary thread terminating.\\n");  
![ExpandedBlockEnd.gif][]\}

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：  
•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）。

•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。

•\_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。

•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。

•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：  
•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。

•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。

[http_www.codeproject.com_useritems_MultithreadingTutorial.asp]: http://www.codeproject.com/useritems/MultithreadingTutorial.asp
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