C++多線程同步技巧(二)--- 事件
阿新 • • 發佈:2018-10-01
create include 解鎖 signed 選擇 參數 bre tdi 人工 函數,導致復位失效,所以在這種情況下,為確保萬無一失,我們一般會再添加一個限制條件,例如臨界區或互斥體;如果選擇的是false,則當一個信號經過 WaitForSingleObject() 函數的時候,函數會自動將事件信號復位。
簡介
Windows在線程同步方面提供了多種信號處理機制,其中一種便是使用 CreateEvent() 函數創建事件,然後使用信號控制同步。其中將事件變為有信號可使用 SetEvent() 函數,將事件信號復位(變為無信號)可使用 ResetEvent() 函數,信號可以配合 WaitForSingleObject() 函數進行控制,當有信號時,此函數便會放行;無信號時,此函數會將阻塞。
提示: CreateEvent() 函數的參數 bManualReset 的含義是信號是否由人工復位,如果選擇true,則信號必須手動采用ResetEvent() 函數進行復位操作,在這種情況下,可能會偶爾出現線程不同的情況,問題出在可能同時會有多個線程穿過 WaitForSingleObject()
代碼樣例
- bManualReset參數為false
//////////////////////////////// // // FileName : ThreadEventDemo.cpp // Creator : PeterZheng // Date : 2018/9/23 18:00 // Comment : The usage of "CreateEvent" // //////////////////////////////// #pragma once #include <cstdio> #include <iostream> #include <cstdlib> #include <windows.h> using namespace std; DWORD WINAPI func1(LPVOID lpParam); DWORD WINAPI func2(LPVOID lpParam); HANDLE hEvent = NULL; unsigned int unCount = 0; DWORD WINAPI func1(LPVOID lpParam) { while (true) { WaitForSingleObject(hEvent, INFINITE); ResetEvent(hEvent); if (unCount < 100) { unCount++; Sleep(10); cout << "Count: " << unCount << endl; SetEvent(hEvent); } else { SetEvent(hEvent); break; } } return 0; } DWORD WINAPI func2(LPVOID lpParam) { while (true) { WaitForSingleObject(hEvent, INFINITE); ResetEvent(hEvent); // 重置事件為無信號狀態 if (unCount < 100) { unCount++; Sleep(10); cout << "Count: " << unCount << endl; SetEvent(hEvent); // 設置事件為有信號狀態 } else { SetEvent(hEvent); break; } } return 0; } int main(void) { HANDLE hThread[2] = { NULL }; hEvent = CreateEvent(NULL, false, false, NULL); //創建一個匿名事件,當參數bManualReset設置為false時 hThread[0] = CreateThread(NULL, 0, func1, NULL, 0, NULL); cout << "Thread-1 is RUNNING" << endl; hThread[1] = CreateThread(NULL, 0, func2, NULL, 0, NULL); cout << "Thread-2 is RUNNING" << endl; SetEvent(hEvent); WaitForMultipleObjects(2, hThread, true, INFINITE); //等待兩個線程運行結束 CloseHandle(hThread[0]); CloseHandle(hThread[1]); CloseHandle(hEvent); system("pause"); return 0; }
- bManualReset參數為true
//////////////////////////////// // // FileName : ThreadEventDemo.cpp // Creator : PeterZheng // Date : 2018/9/23 18:00 // Comment : The usage of "CreateEvent" // //////////////////////////////// #pragma once #include <cstdio> #include <iostream> #include <cstdlib> #include <windows.h> using namespace std; DWORD WINAPI func1(LPVOID lpParam); DWORD WINAPI func2(LPVOID lpParam); HANDLE hEvent = NULL; HANDLE hMutex = NULL; unsigned int unCount = 0; DWORD WINAPI func1(LPVOID lpParam) { while (true) { WaitForSingleObject(hEvent, INFINITE); WaitForSingleObject(hMutex, INFINITE); //為互斥體上鎖 ResetEvent(hEvent); // 重置事件為無信號狀態 if (unCount < 100) { unCount++; Sleep(10); cout << "Count: " << unCount << endl; SetEvent(hEvent); // 設置事件為有信號狀態 ReleaseMutex(hMutex); //互斥體解鎖 } else { SetEvent(hEvent); ReleaseMutex(hMutex); break; } } return 0; } DWORD WINAPI func2(LPVOID lpParam) { while (true) { WaitForSingleObject(hEvent, INFINITE); WaitForSingleObject(hMutex, INFINITE); //為互斥體上鎖 ResetEvent(hEvent); // 重置事件為無信號狀態 if (unCount < 100) { unCount++; Sleep(10); cout << "Count: " << unCount << endl; SetEvent(hEvent); // 設置事件為有信號狀態 ReleaseMutex(hMutex); } else { SetEvent(hEvent); ReleaseMutex(hMutex); break; } } return 0; } int main(void) { HANDLE hThread[2] = { NULL }; hEvent = CreateEvent(NULL, true, false, NULL); //創建一個匿名事件,當參數bManualReset設置為true時 hMutex = CreateMutex(NULL, false, NULL); //創建一個匿名互斥體 hThread[0] = CreateThread(NULL, 0, func1, NULL, 0, NULL); cout << "Thread-1 is RUNNING" << endl; hThread[1] = CreateThread(NULL, 0, func2, NULL, 0, NULL); cout << "Thread-2 is RUNNING" << endl; SetEvent(hEvent); // 設置事件為有信號狀態 WaitForMultipleObjects(2, hThread, true, INFINITE); //等待兩個線程運行結束 CloseHandle(hThread[0]); CloseHandle(hThread[1]); CloseHandle(hEvent); CloseHandle(hMutex); system("pause"); return 0; }
C++多線程同步技巧(二)--- 事件