多线程同步中的读者写者问题 － linux 平台实现

linux 平台下的实现与 windows 很相似，只有一些代码上的小的差别。

1： ReaderWriterLock.h， 该文件定义了读写锁的类

#ifndef ReaderWriterLock_H
#define ReaderWriterLock_H

#include <bits/pthreadtypes.h>
#include <semaphore.h>

class ReaderWriterLock
{
protected:
       pthread_mutex_t readMutex;
       sem_t writeSemaph;
       int numReaders;

public:
       ReaderWriterLock()
       {
              numReaders = 0;

              // create 1 Mutex and 1 Semaphore
              // 2 Semaphore also OK
              pthread_mutex_init(&readMutex, NULL);
              sem_init(&writeSemaph, 0, 1);
       }

       ~ReaderWriterLock()
       {
               pthread_mutex_destroy(&readMutex);
               sem_destroy(&writeSemaph);
       }
       inline void ReaderLock()
       {
              // lock readMutex for readers to access numReaders
              pthread_mutex_lock(&readMutex);
              numReaders++;
              if (1 == numReaders)
              {
                     // for first reader, lock writeSemaph
                     sem_wait(&writeSemaph);
              }
              pthread_mutex_unlock(&readMutex);
       }

       inline void ReaderUnLock()
       {
              // lock readMutex for readers to access numReaders
              pthread_mutex_lock(&readMutex);
              numReaders--;
              if (numReaders == 0)
              {
                     // for last reader, unlock writeSemaph
                     sem_post(&writeSemaph);
              }
              pthread_mutex_unlock(&readMutex);
       }

       inline void WriterLock()
       {
              // lock writeSemaph for writers to access shared object
              sem_wait(&writeSemaph);
       }

       inline void WriterUnLock()
       {
              // unlock writeSemaph for writers to access shared object
              sem_post(&writeSemaph);
       }
};

#endif

2：ReaderWriter.cpp， 该文件是测试程序，在 Linux 上调试通过

#include <iostream>
#include <string>
#include <pthread.h>
#include <unistd.h>

using namespace std;

#include "ReaderWriterLock.h"
#include "RasUtil.h"

char sharedStr[128]="this is a shared string !";
ReaderWriterLock* rwLock=new ReaderWriterLock();
char logFile[128]="log";

void* readerProc(void* param);
void* writerProc(void* param);
void WriteLogStr(char* s);

int main(int argc, char* argv[])
{
       int ret;
       pthread_t reader1;
       pthread_t reader2;
       pthread_t reader3;
       pthread_t writer1;
       pthread_t writer2;
       int readerId;
       int writerId;
       FILE* f;

       // clear the log
       f = fopen(logFile, "w");
       fclose(f);

       // init random seed
       srand(getpid());

       readerId = 1;
       pthread_create(&reader1, NULL, readerProc, (void*)(&readerId));
       sleep(1);

       writerId = 1;
       pthread_create(&writer1, NULL, writerProc, (void*)&writerId);
        sleep(1);

       readerId = 2;
       pthread_create(&reader2, NULL, readerProc, (void*)&readerId);
       sleep(1);

       writerId = 2;
       pthread_create(&writer2, NULL, writerProc, (void*)&writerId);
       sleep(1);

       readerId = 3;
       pthread_create(&reader3, NULL, readerProc, (void*)&readerId);

       sleep(5);

       return 0;
}

void* readerProc(void* param)
{
       int myid;
       char idStr[128];
       char str[128];

       myid = *((int*)(param));
       RasUtil::intToStr(myid, idStr);

       strcpy(str, "reader ");
       strncat(str, idStr, 128);
       strcat(str, " begin......");

       cout << "reader " << myid << " begin......" << endl;
       WriteLogStr(str);

       while (true)
       {
              // first sleep a random time : between 1 - 5 s
              int sleepTime; 
              sleepTime = 1 + (int)(5.0*rand()/(RAND_MAX+1.0)); 
              usleep(sleepTime*10);

              // prepare str
              strcpy(str, "reader ");
              strncat(str, idStr, 128);
              strcat(str, " is reading the shared string :    ");

              // then access the shared var
              rwLock->ReaderLock();
              strncat(str, sharedStr, 128);
              rwLock->ReaderUnLock();

              cout << "reader " << myid << " is reading the shared string    : " << sharedStr << endl;
              WriteLogStr(str);
       }
}

void* writerProc(void* param)
{
       int myid;
       char idStr[128];
       char str[128];

       myid = *((int*)(param));
       RasUtil::intToStr(myid, idStr);

       strcpy(str, "writer ");
       strncat(str, idStr, 128);
       strcat(str, " begin......");

       cout << "writer " << myid << " begin......" << endl;
       WriteLogStr(str);

       while (true)
       {
              // get a random char
              int randChar; 
              randChar = myid + (int)(5.0*rand()/(RAND_MAX+1.0)); 
              randChar += 40;

              // then access the shared var
              rwLock->WriterLock();
              for (int i=0; i<20; i++)
               {
                      sharedStr[i] = randChar;
                      usleep(1);
               }
               sharedStr[20] = 0; // append a '\0' to end a string

               strcpy(str, "writer ");
               strncat(str, idStr, 128);
               strcat(str, " is writing the shared string to : ");
               strncat(str, sharedStr, 128);
              rwLock->WriterUnLock();

              cout << "writer " << myid << " is writing the shared string to : " << sharedStr << endl;
              WriteLogStr(str);
       }
}

void WriteLogStr(char* s)
{
       FILE* f;

       f = fopen(logFile, "a");
       if (f != NULL)
      {
              fwrite(s, strlen(s), 1, f);
              fwrite("\n", 1, 1, f);
       }

       fclose(f);
}

3：RasUtil.h，完成整数转换为字符串

#ifndef _RasUtil_h_
#define _RasUtil_h_

class RasUtil
{
public:
       static inline void intToStr(int i, char* str);

};

inline void RasUtil::intToStr(int i, char* str)
{
    int dec;
    int sign;
    char* p;

    p = ecvt(i, 10, &dec, &sign);
    strcpy(str, p);
    str[dec] = 0;
}

#endif