C++多線程（二）(_beginThreadex創建多線程)??
C/C++ Runtime 多線程函數
一 簡單實例（來自codeprojct：http://www.codeproject.com/useritems/MultithreadingTutorial.asp）
主線程創建2個線程t1和t2，創建時2個線程就被掛起，后來調用ResumeThread恢復2個線程，是其開始執行，調用WaitForSingleObject等待2個線程執行完，然后推出主線程即結束進程。
/*??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?);//你需要恢復線程的句柄 使用該函數能夠激活線程的運行????//?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 函數用來檢測 hHandle 事件的信號狀態，當函數的執行時間超過 dwMilliseconds 就返回，
???? //但如果參數 dwMilliseconds 為 INFINITE 時函數將直到相應時間事件變成有信號狀態才返回，否則就一直等待下去
???? //，直到 WaitForSingleObject 有返回直才執行后面的代碼
????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這個函數是獲得線程的退出碼， 第二個參數是一個 DWORD的指針，
//用戶應該使用一個 DWORD 類型的變量去接收數據，返回的數據是線程的退出碼，
//第一個參數是線程句柄，用 CreateThread 創建線程時獲得到。
//通過線程退出碼可以判斷線程是否正在運行，還是已經退出。 ????//?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");}
二解釋
1）如果你正在編寫C/C++代碼，決不應該調用CreateThread。相反，應該使用VisualC++運行期庫函數_beginthreadex，推出也應該使用_endthreadex。如果不使用Microsoft的VisualC++編譯器，你的編譯器供應商有它自己的CreateThred替代函數。不管這個替代函數是什么，你都必須使用。
2）因為_beginthreadex和_endthreadex是CRT線程函數，所以必須注意編譯選項runtimelibaray的選擇，使用MT或MTD。
3) _beginthreadex函數的參數列表與CreateThread函數的參數列表是相同的，但是參數名和類型并不完全相同。這是因為Microsoft的C/C++運行期庫的開發小組認為，C/C++運行期函數不應該對Windows數據類型有任何依賴。_beginthreadex函數也像CreateThread那樣，返回新創建的線程的句柄。
下面是關于_beginthreadex的一些要點：
&8226;每個線程均獲得由C/C++運行期庫的堆棧分配的自己的tiddata內存結構。（tiddata結構位于Mtdll.h文件中的VisualC++源代碼中）。
&8226;傳遞給_beginthreadex的線程函數的地址保存在tiddata內存塊中。傳遞給該函數的參數也保存在該數據塊中。
&8226;_beginthreadex確實從內部調用CreateThread，因為這是操作系統了解如何創建新線程的唯一方法。
&8226;當調用CreatetThread時，它被告知通過調用_threadstartex而不是pfnStartAddr來啟動執行新線程。還有，傳遞給線程函數的參數是tiddata結構而不是pvParam的地址。
&8226;如果一切順利，就會像CreateThread那樣返回線程句柄。如果任何操作失敗了，便返回NULL。
4) _endthreadex的一些要點：
&8226;C運行期庫的_getptd函數內部調用操作系統的TlsGetValue函數，該函數負責檢索調用線程的tiddata內存塊的地址。
&8226;然后該數據塊被釋放，而操作系統的ExitThread函數被調用，以便真正撤消該線程。當然，退出代碼要正確地設置和傳遞。
5)雖然也提供了簡化版的的_beginthread和_endthread，但是可控制性太差，所以一般不使用。
6）線程handle因為是內核對象，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++主線程的終止，同時也會終止所有主線程創建的子線程，不管子線程有沒有執行完畢。所以上面的代碼中如果不調用WaitForSingleObject，則2個子線程t1和t2可能并沒有執行完畢或根本沒有執行。
2）如果某線程掛起，然后有調用WaitForSingleObject等待該線程，就會導致死鎖。所以上面的代碼如果不調用resumethread，則會死鎖。
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為什么要用C運行時庫的_beginthreadex代替操作系統的CreateThread來創建線程？
來源自自1999年7月MSJ雜志的《Win32 Q&A》欄目
你也許會說我一直用CreateThread來創建線程，一直都工作得好好的，為什么要用_beginthreadex來代替CreateThread，下面讓我來告訴你為什么。
回答一個問題可以有兩種方式，一種是簡單的，一種是復雜的。
如果你不愿意看下面的長篇大論，那我可以告訴你簡單的答案：_beginthreadex在內部調用了CreateThread，在調用之前_beginthreadex做了很多的工作，從而使得它比CreateThread更安全。
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