一、 概述
C++多线程开发中,容易出现死锁导致程序挂起的现象。
关于死锁的信息,见百度百科http://baike.baidu.com/view/121723.htm。
解决步骤分为三步:
1、检测死锁线程。
2、打印线程信息。
3、修改死锁程序。
二、 程序示例
VS2005创建支持MFC的win32控制台程序。
代码见示例代码DeadLockTest.cpp。
[cpp] view plaincopy
- // DeadLockTest.cpp : Defines the entry point for the console application.
- //
- #include "stdafx.h"
- #include "DeadLockTest.h"
- #ifdef _DEBUG
- #define new DEBUG_NEW
- #endif
- // The one and only application object
- CWinApp theApp;
- using namespace std;
- CRITICAL_SECTION cs1;
- CRITICAL_SECTION cs2;
- CRITICAL_SECTION csprint;
- //初始化关键代码段
- void InitMyCriticalSection();
- //删除关键代码段
- void DeleteMyCriticalSection();
- //打印信息
- void PrintString(const CString& strInfo);
- DWORD WINAPI Thread1(LPVOID lpParameter);
- DWORD WINAPI Thread2(LPVOID lpParameter);
- int _tmain(int argc, TCHAR* argv[], TCHAR* envp[])
- {
- int nRetCode = 0;
- // initialize MFC and print and error on failure
- if (!AfxWinInit(::GetModuleHandle(NULL), NULL, ::GetCommandLine(), 0))
- {
- // TODO: change error code to suit your needs
- _tprintf(_T("Fatal Error: MFC initialization failed\n"));
- nRetCode = 1;
- return nRetCode;
- }
- //初始化关键代码段
- InitMyCriticalSection();
- //创建线程
- HANDLE hThread1 = CreateThread(NULL, 0, Thread1, NULL, 0, NULL);
- HANDLE hThread2 = CreateThread(NULL, 0, Thread2, NULL, 0, NULL);
- //等待线程结束
- WaitForSingleObject(hThread1, INFINITE);
- WaitForSingleObject(hThread2, INFINITE);
- //关闭线程句柄
- CloseHandle(hThread1);
- CloseHandle(hThread2);
- //释放关键代码段
- DeleteMyCriticalSection();
- return nRetCode;
- }
- void InitMyCriticalSection()
- {
- InitializeCriticalSection(&cs1);
- InitializeCriticalSection(&cs2);
- InitializeCriticalSection(&csprint);
- }
- void DeleteMyCriticalSection()
- {
- DeleteCriticalSection(&cs1);
- DeleteCriticalSection(&cs2);
- DeleteCriticalSection(&csprint);
- }
- DWORD WINAPI Thread1(LPVOID lpParameter)
- {
- for (int i = 0; i < 5; i++)
- {
- EnterCriticalSection(&cs1);
- Sleep(500);
- EnterCriticalSection(&cs2);
- PrintString(_T("Thread1"));
- LeaveCriticalSection(&cs2);
- LeaveCriticalSection(&cs1);
- }
- return 1;
- }
- DWORD WINAPI Thread2(LPVOID lpParameter)
- {
- for (int i = 0; i < 5; i++)
- {
- EnterCriticalSection(&cs2);
- Sleep(500);
- EnterCriticalSection(&cs1);
- PrintString(_T("Thread2"));
- LeaveCriticalSection(&cs1);
- LeaveCriticalSection(&cs2);
- }
- return 1;
- }
- void PrintString(const CString& strInfo)
- {
- EnterCriticalSection(&csprint);
- wcout<<(const TCHAR*)strInfo<<endl;
- LeaveCriticalSection(&csprint);
- }
运行DeadLockTest.exe,程序挂起。
三、 死锁检测
检测工具见《Windows核心编程》,第9章9.8.6节LockCop检测工具。
工具源码地址:http://www1.wintellect.com/Resources/Details/86。
LockCop可使用vs2010编译成功。
备注:该工具使用了Windows Vista/ 7提供的WCT API,故需要在Windows Vista/ 7系统运行LockCop检测工具。
检测,挂起的DeadLockTest.exe,得到线程信息。
检测到程序挂起由死锁引起。
线程4014:等待线程772、线程4012完成。
线程772:拥有关键代码段A,等待关键代码段B(被线程4012拥有)。
线程4012:拥有关键代码段B,等待关键代码段A(被线程772拥有)。
线程772与4012互相等待,程序发生死锁现象。
四、 打印信息
为了便于查找问题,我们加上线程打印信息。
打印线程名称、线程ID以及关键代码段进入信息。
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- DWORD WINAPI Thread1(LPVOID lpParameter)
- {
- CString strThreadID = _T("");
- strThreadID.Format(_T("%d"), GetCurrentThreadId());
- CString strPrintInfo = _T("");
- for (int i = 0; i < 5; i++)
- {
- EnterCriticalSection(&cs1);
- strPrintInfo = _T("");
- strPrintInfo += _T("Thread1 ");
- strPrintInfo += strThreadID;
- strPrintInfo += _T(" EnterCriticalSection(&cs1)");
- PrintString(strPrintInfo);
- Sleep(500);
- EnterCriticalSection(&cs2);
- strPrintInfo = _T("");
- strPrintInfo += _T("Thread1 ");
- strPrintInfo += strThreadID;
- strPrintInfo += _T(" EnterCriticalSection(&cs2)");
- PrintString(strPrintInfo);
- LeaveCriticalSection(&cs2);
- LeaveCriticalSection(&cs1);
- }
- return 1;
- }
- DWORD WINAPI Thread2(LPVOID lpParameter)
- {
- CString strThreadID = _T("");
- strThreadID.Format(_T("%d"), GetCurrentThreadId());
- CString strPrintInfo = _T("");
- for (int i = 0; i < 5; i++)
- {
- EnterCriticalSection(&cs2);
- strPrintInfo = _T("");
- strPrintInfo += _T("Thread2 ");
- strPrintInfo += strThreadID;
- strPrintInfo += _T(" EnterCriticalSection(&cs2)");
- PrintString(strPrintInfo);
- Sleep(500);
- EnterCriticalSection(&cs1);
- strPrintInfo = _T("");
- strPrintInfo += _T("Thread2 ");
- strPrintInfo += strThreadID;
- strPrintInfo += _T(" EnterCriticalSection(&cs1)");
- PrintString(strPrintInfo);
- LeaveCriticalSection(&cs1);
- LeaveCriticalSection(&cs2);
- }
- return 1;
- }
运行结果如下。
五、 死锁修改
线程互斥进行修改,Thread1与Thread2对关键代码段的进入与退出顺序改为相同。程序运行正常。
修改后线程代码。
[cpp] view plaincopy
- DWORD WINAPI Thread1(LPVOID lpParameter)
- {
- for (int i = 0; i < 5; i++)
- {
- EnterCriticalSection(&cs1);
- Sleep(500);
- EnterCriticalSection(&cs2);
- PrintString(_T("Thread1"));
- LeaveCriticalSection(&cs2);
- LeaveCriticalSection(&cs1);
- }
- return 1;
- }
- DWORD WINAPI Thread2(LPVOID lpParameter)
- {
- for (int i = 0; i < 5; i++)
- {
- EnterCriticalSection(&cs1);
- Sleep(500);
- EnterCriticalSection(&cs2);
- PrintString(_T("Thread2"));
- LeaveCriticalSection(&cs2);
- LeaveCriticalSection(&cs1);
- }
- return 1;
- }