C++死锁解决心得

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。

// 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 objectCWinApp 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。

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。

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;}