读者写者问题

参考地址：http://blog.csdn.net/morewindows/article/details/7596034

读者写者问题描述非常简单，有一个写者很多读者，多个读者可以同时读文件，但写者在写文件时不允许有读者在读文件，同样有读者在读文件时写者也不去能写文件。类似于生产者消费者问题的分析过程，首先来找找哪些是属于“等待”情况。

第一．写者要等到没有读者时才能去写文件。

第二．所有读者要等待写者完成写文件后才能去读文件。

参考博客里边有Bug，自己想着写的，不知道还有问题没，欢迎拍砖。。。。。。

解法一：

  1 #include <iostream>
  2 #include <string>
  3 #include <Windows.h>
  4 #include <process.h>
  5 using namespace std;
  6 
  7 /************************************************************************************
  8 
  9                            模拟读者写者问题:1个写者，5个读者
 10 
 11 *************************************************************************************/
 12 
 13 CRITICAL_SECTION g_csStdout;
 14 CRITICAL_SECTION g_csReaderCnt;
 15 CRITICAL_SECTION g_csReaderWriter;//防止在没有读者也没有写者的情况下出现同时读写的情况
 16 const int READER_NUM = 5;    //读者个数
 17 HANDLE g_EventNoReader;
 18 HANDLE g_EventNoWriter;
 19 int g_nCurrentReaderCnt;
 20 
 21 //设置控制台文字颜色
 22 BOOL SetConsoleColor(WORD wAttributes)
 23 {
 24     HANDLE hHandle = GetStdHandle(STD_OUTPUT_HANDLE);
 25     if (hHandle == INVALID_HANDLE_VALUE)
 26     {
 27         cout << "GetStdHandle Error!" << endl;
 28         return false;
 29     }
 30     //SetConsoleTitle(L"读者写者问题");
 31     return SetConsoleTextAttribute(hHandle, wAttributes);
 32 }
 33 
 34 void PrintWriterLog(string strLog)
 35 {
 36     EnterCriticalSection(&g_csStdout);
 37     SetConsoleColor(FOREGROUND_GREEN);
 38     cout << strLog << endl;
 39     SetConsoleColor(FOREGROUND_GREEN|FOREGROUND_BLUE|FOREGROUND_RED);
 40     LeaveCriticalSection(&g_csStdout);
 41 }
 42 unsigned int WINAPI WriterThreadFunc(PVOID pParam)
 43 {
 44     volatile int nCnt = 0;
 45     while(nCnt++ < 5)
 46     {
 47         PrintWriterLog("写者线程等待中...
");
 48 
 49         EnterCriticalSection(&g_csReaderWriter);
 50         WaitForSingleObject(g_EventNoReader, INFINITE);
 51         //标记写者正在写文件
 52         ResetEvent(g_EventNoWriter);
 53 
 54         PrintWriterLog("写者开始写文件
");
 55         //do something--writing file
 56 
 57         Sleep(rand()%100);
 58         PrintWriterLog("写者结束写文件
");
 59 
 60         SetEvent(g_EventNoWriter);
 61 
 62         //因为g_EventNoReader是自动复位用以防止出现多个写线程同时写的情况，但是写线程退出时应将此信号重新改为触发
 63         SetEvent(g_EventNoReader);
 64 
 65         LeaveCriticalSection(&g_csReaderWriter);
 66 
 67         Sleep(2000);
 68     }
 69     
 70     return 0;
 71 }
 72 
 73 void PrintReaderLog(string strFormat, ...)
 74 {
 75     va_list va;
 76     va_start(va, strFormat);
 77     EnterCriticalSection(&g_csStdout);
 78     SetConsoleColor(FOREGROUND_GREEN|FOREGROUND_BLUE|FOREGROUND_RED);
 79     vfprintf_s(stdout, strFormat.c_str(), va);
 80     LeaveCriticalSection(&g_csStdout);
 81     va_end(va);
 82 }
 83 unsigned int WINAPI ReaderThreadFunc(PVOID pParam)
 84 {
 85     PrintReaderLog("读者线程[%d]等待中...
", GetCurrentThreadId());
 86     WaitForSingleObject(g_EventNoWriter, INFINITE);
 87     EnterCriticalSection(&g_csReaderCnt);
 88     ++g_nCurrentReaderCnt;
 89     if (g_nCurrentReaderCnt == 1)
 90     {//g_csReaderWriter防止在未改变g_EventNoReader为未触发状态之前，写线程获得信号，此时会出现同时读写的情况
 91         EnterCriticalSection(&g_csReaderWriter);
 92         ResetEvent(g_EventNoReader);
 93         LeaveCriticalSection(&g_csReaderWriter);
 94     }
 95     LeaveCriticalSection(&g_csReaderCnt);
 96 
 97     PrintReaderLog("读者线程[%d]开始读文件
", GetCurrentThreadId());
 98     //do something---reading file
 99     Sleep(rand()%100);
100     PrintReaderLog("读者线程[%d]结束读文件
", GetCurrentThreadId());
101 
102     EnterCriticalSection(&g_csReaderCnt);
103     --g_nCurrentReaderCnt;
104     if (g_nCurrentReaderCnt == 0)
105         SetEvent(g_EventNoReader);
106     LeaveCriticalSection(&g_csReaderCnt);
107 
108     return 0;
109 }
110 
111 int main()
112 {
113     HANDLE hThread[READER_NUM+1];
114     g_EventNoWriter = CreateEvent(NULL, false, true, NULL);
115     g_EventNoReader = CreateEvent(NULL, true, true, NULL);
116     InitializeCriticalSection(&g_csReaderCnt);
117     InitializeCriticalSection(&g_csStdout);
118     InitializeCriticalSection(&g_csReaderWriter);
119     cout << "		读者写者问题" << endl << endl;
120 
121     //先启两个读线程
122     for (int i = 1; i <= 2; ++i)
123         hThread[i] = (HANDLE)_beginthreadex(NULL, 0, ReaderThreadFunc, NULL, 0, NULL);
124     //启动一个写线程
125     hThread[0] = (HANDLE)_beginthreadex(NULL, 0, WriterThreadFunc, NULL, 0, NULL);
126     Sleep(50);
127     //启动其他读线程
128     for (int i = 3; i <= READER_NUM; ++i)
129         hThread[i] = (HANDLE)_beginthreadex(NULL, 0, ReaderThreadFunc, NULL, 0, NULL);
130 
131     WaitForMultipleObjects(READER_NUM+1, hThread, true, INFINITE);
132     
133     for (int i = 0; i <= READER_NUM+1; ++i)
134         CloseHandle(hThread[i]);
135     CloseHandle(g_EventNoWriter);
136     CloseHandle(g_EventNoReader);
137     DeleteCriticalSection(&g_csStdout);
138     DeleteCriticalSection(&g_csReaderCnt);
139     DeleteCriticalSection(&g_csReaderWriter);
140 
141     return 0;
142 }

解法二：读写锁SRWLock

注意事项：一个线程仅能锁定资源一次，不能多次锁定资源。

  1 #include <iostream>
  2 #include <string>
  3 #include <Windows.h>
  4 #include <process.h>
  5 using namespace std;
  6 
  7 /************************************************************************************
  8 
  9                       读写锁SRWLock---模拟读者写者问题:1个写者，5个读者
 10 
 11 *************************************************************************************/
 12 
 13 CRITICAL_SECTION g_csStdout;
 14 SRWLOCK g_srwLock;            //读写锁
 15 const int READER_NUM = 5;    //读者个数
 16 
 17 
 18 //设置控制台文字颜色
 19 BOOL SetConsoleColor(WORD wAttributes)
 20 {
 21     HANDLE hHandle = GetStdHandle(STD_OUTPUT_HANDLE);
 22     if (hHandle == INVALID_HANDLE_VALUE)
 23     {
 24         cout << "GetStdHandle Error!" << endl;
 25         return false;
 26     }
 27     //SetConsoleTitle(L"读者写者问题");
 28     return SetConsoleTextAttribute(hHandle, wAttributes);
 29 }
 30 
 31 void PrintWriterLog(string strLog)
 32 {
 33     EnterCriticalSection(&g_csStdout);
 34     SetConsoleColor(FOREGROUND_GREEN);
 35     cout << strLog << endl;
 36     SetConsoleColor(FOREGROUND_GREEN|FOREGROUND_BLUE|FOREGROUND_RED);
 37     LeaveCriticalSection(&g_csStdout);
 38 }
 39 unsigned int WINAPI WriterThreadFunc(PVOID pParam)
 40 {
 41     volatile int nCnt = 0;
 42     while(nCnt++ < 5)
 43     {
 44         PrintWriterLog("写者线程等待中...
");
 45         //申请写文件排它锁
 46         AcquireSRWLockExclusive(&g_srwLock);
 47         
 48         PrintWriterLog("写者开始写文件
");
 49         //do something--writing file
 50         Sleep(rand()%100);
 51 
 52         
 53         PrintWriterLog("写者结束写文件
");
 54         //释放锁
 55         ReleaseSRWLockExclusive(&g_srwLock);
 56         Sleep(2000);
 57     }
 58     
 59     return 0;
 60 }
 61 
 62 void PrintReaderLog(string strFormat, ...)
 63 {
 64     va_list va;
 65     va_start(va, strFormat);
 66     EnterCriticalSection(&g_csStdout);
 67     SetConsoleColor(FOREGROUND_GREEN|FOREGROUND_BLUE|FOREGROUND_RED);
 68     vfprintf_s(stdout, strFormat.c_str(), va);
 69     LeaveCriticalSection(&g_csStdout);
 70     va_end(va);
 71 }
 72 unsigned int WINAPI ReaderThreadFunc(PVOID pParam)
 73 {
 74     PrintReaderLog("读者线程[%d]等待中...
", GetCurrentThreadId());
 75     //读者申请读取文件
 76     AcquireSRWLockShared(&g_srwLock);
 77     
 78     PrintReaderLog("读者线程[%d]开始读文件
", GetCurrentThreadId());
 79     //do something---reading file
 80     Sleep(rand()%100);
 81     
 82     PrintReaderLog("读者线程[%d]结束读文件
", GetCurrentThreadId());
 83     //释放读取锁
 84     ReleaseSRWLockShared(&g_srwLock);
 85     return 0;
 86 }
 87 
 88 int main()
 89 {
 90     HANDLE hThread[READER_NUM+1];
 91 
 92     InitializeCriticalSection(&g_csStdout);
 93     InitializeSRWLock(&g_srwLock);
 94     cout << "		读者写者问题---读写锁SRWLock" << endl << endl;
 95 
 96     //先启两个读线程
 97     for (int i = 1; i <= 2; ++i)
 98         hThread[i] = (HANDLE)_beginthreadex(NULL, 0, ReaderThreadFunc, NULL, 0, NULL);
 99     //启动一个写线程
100     hThread[0] = (HANDLE)_beginthreadex(NULL, 0, WriterThreadFunc, NULL, 0, NULL);
101     Sleep(50);
102     //启动其他读线程
103     for (int i = 3; i <= READER_NUM; ++i)
104         hThread[i] = (HANDLE)_beginthreadex(NULL, 0, ReaderThreadFunc, NULL, 0, NULL);
105 
106     WaitForMultipleObjects(READER_NUM+1, hThread, true, INFINITE);
107     
108     for (int i = 0; i <= READER_NUM+1; ++i)
109         CloseHandle(hThread[i]);
110 
111     DeleteCriticalSection(&g_csStdout);
112 
113     return 0;
114 }

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原文地址：https://www.cnblogs.com/dongsheng/p/5086623.html