線程同步技術

（1）互斥對象：函數CreateMutex。在多核下工作不正常。
（2）事件對象：函數CreateEvent、SetEvent、ResetEvent、WaitForSingleObject，應當使用自動重置的事件對象。在多核下工作正常。
（3）關鍵代碼段：類CRITICAL_SECTION，函數InitializeCriticalSection、DeleteCriticalSection、EnterCriticalSection、LeaveCriticalSection。在多核下工作基本正常，但是會出現：“"xxx"指令引用的"xxx"內存。該內存不能爲"written"。”。需要注意線程死鎖問題。

三者比較：
互斥對象和事件對象都屬於內核對象，速度較慢。但可以在多個進程中的各個線程間進行同步。
關鍵代碼段工作在用戶方式下，同步速度較快，但容易進入死鎖狀態，因爲在等待進入關鍵代碼段時無法設定超時值。通常，首選關鍵代碼段。
其使用也比較簡單，如果在MFC中的話，可在構造函數調用InitializeCriticalSection，在構造函數調用DeleteCriticalSection，在所需保護的代碼前調用EnterCriticalSection，在訪問完所需保護的資源後調用LeaveCriticalSection即可。

 

----------------例子：互斥對象------------------------------------------------

#include <windows.h> #include <iostream.h> int index=0; int tickets=20; HANDLE hMutex; DWORD WINAPI Fun1Proc(LPVOID lpPrama) { while(TRUE) { WaitForSingleObject(hMutex,INFINITE); if (tickets>0) { Sleep(1); cout<<"thread 1 sell ticket: "<<tickets--<<endl; } else { break; } ReleaseMutex(hMutex); } return 0; } DWORD WINAPI Fun2Proc(LPVOID lpPrama) { while(TRUE) { WaitForSingleObject(hMutex,INFINITE); if (tickets>0) { Sleep(1); cout<<"thread 2 sell ticket: "<<tickets--<<endl; } else { break; } ReleaseMutex(hMutex); } return 0; } void main() { HANDLE hThread1; HANDLE hThread2; hThread1=CreateThread(NULL,0,Fun1Proc,NULL,0,NULL); hThread2=CreateThread(NULL,0,Fun2Proc,NULL,0,NULL); CloseHandle(hThread1); CloseHandle(hThread2); hMutex=CreateMutex(NULL,FALSE,NULL); Sleep(1000); }

正確的結果是由20遞減到1，但是本程序會出現以下錯誤結果：
thread 1 sell ticket: 20
thread 1 sell ticket: 20
thread 2 sell ticket: 19
thread 1 sell ticket: 18
...
thread 2 sell ticket: 1
----------------------------------------------------------------------------------

 

----------------例子：事件對象------------------------------------------------

#include <windows.h> #include <iostream.h> int tickets=20; HANDLE g_hEvent; DWORD WINAPI Fun1Proc(LPVOID lpPrama) { while(TRUE) { WaitForSingleObject(g_hEvent,INFINITE); //ResetEvent(g_hEvent); if (tickets>0) { Sleep(1); cout<<"thread 1 sell ticket: "<<tickets--<<endl; SetEvent(g_hEvent); } else { SetEvent(g_hEvent); break; } } return 0; } DWORD WINAPI Fun2Proc(LPVOID lpPrama) { while(TRUE) { WaitForSingleObject(g_hEvent,INFINITE); //ResetEvent(g_hEvent); if (tickets>0) { Sleep(1); cout<<"thread 2 sell ticket: "<<tickets--<<endl; SetEvent(g_hEvent); } else { SetEvent(g_hEvent); break; } } return 0; } void main() { HANDLE hThread1; HANDLE hThread2; g_hEvent=CreateEvent(NULL,FALSE,FALSE,NULL); SetEvent(g_hEvent); hThread1=CreateThread(NULL,0,Fun1Proc,NULL,0,NULL); hThread2=CreateThread(NULL,0,Fun2Proc,NULL,0,NULL); CloseHandle(hThread1); CloseHandle(hThread2); Sleep(1000); CloseHandle(g_hEvent); }

 

----------------例子：關鍵代碼段---------------------------------------------

//<QA>註釋掉兩個Mark的代碼行後，出現內存不能寫異常。 #include <windows.h> #include <iostream.h> int tickets=20; CRITICAL_SECTION g_cs; DWORD WINAPI Fun1Proc(LPVOID lpPrama) { while(TRUE) { EnterCriticalSection(&g_cs); Sleep(1); //Mark if (tickets>0) { Sleep(1); cout<<"thread 1 sell ticket: "<<tickets--<<endl; LeaveCriticalSection(&g_cs); } else { LeaveCriticalSection(&g_cs); break; } } return 0; } DWORD WINAPI Fun2Proc(LPVOID lpPrama) { while(TRUE) { EnterCriticalSection(&g_cs); Sleep(1); //Mark if (tickets>0) { Sleep(1); cout<<"thread 2 sell ticket: "<<tickets--<<endl; LeaveCriticalSection(&g_cs); } else { LeaveCriticalSection(&g_cs); break; } } return 0; } void main() { HANDLE hThread1; HANDLE hThread2; hThread1=CreateThread(NULL,0,Fun1Proc,NULL,0,NULL); hThread2=CreateThread(NULL,0,Fun2Proc,NULL,0,NULL); CloseHandle(hThread1); CloseHandle(hThread2); InitializeCriticalSection(&g_cs); Sleep(1000); DeleteCriticalSection(&g_cs); }