读者写者 问题C线程实现 linux平台

1、首先 读者写者的信号量实现

设置三个互斥信号量：

• rwmutex 用于写者与其他读者/写者互斥的访问共享数据
• rmutex  用于读者互斥的访问读者计数器readcount
• wmutex 用于写者等待已进入读者退出，所有读者退出前互斥写操作

• var rwmutex, rmutex，wmutex ： semaphore := 1，1，1 ；
  int readcount = 0;
  cobegin
         readeri begin  // i=1,2,….
                P(rwmutex);
                P(rmutex);
                Readcount++;
                If (readcount == 1) P(wmutex); //有读者进入，互斥写操作
                V(rmutex);
                V(rwmutex); // 及时释放读写互斥信号量，允许其它读、写进程申请资源
                读数据；
                P(rmutex);
                Readcount--;
                If (readcount == 0) V(wmutex); //所有读者退出，允许写更新
                V(rmutex);
         End
  
         Writerj begin // j = 1,2,….
                P(rwmutex);  // 互斥后续其它读者、写者
                P(wmutex);  //如有读者正在读，等待所有读者读完
                写更新；
                V(wmutex);   //允许后续新的第一个读者进入后互斥写操作
                V(rwmutex);  //允许后续新读者及其它写者
         End
  Coend

  
  

  2 然后再linux平台下 我用到了 pthread_creat  , pthread_mutex_trylock  , pthread_mutex_unlock ;

  代码实现，肯定还存在bug ，希望路过的同学批评指正。

  #include 
  #include         /* for convenience */
  #include         /* for offsetof */
  #include         /* for convenience */
  #include         /* for convenience */
  #include         /* for SIG_ERR */
  #include 
  #include 
  
  pthread_mutex_t rwlock = PTHREAD_MUTEX_INITIALIZER; /*对缓冲访问的互斥*/
  pthread_mutex_t rlock = PTHREAD_MUTEX_INITIALIZER; /*对readcount访问的互斥*/
  pthread_mutex_t wlock = PTHREAD_MUTEX_INITIALIZER; /*write 线程 访问互斥*/
  int readcount ;
  int readpos ,writepos ;
  const int N = 10;
  int pool[10];
  pthread_t pthreadarray[10];
  void print()
  {
      int i;
      printf("\n\n and now the pool is \n");
      for(i = 0 ; i < N ; i ++)
          printf("%d  is : %d\n ",i,pool[i]);
      sleep(2);
  }
  pthread_t find(pthread_t tid)
  {
      int i;
      for(i = 0 ; i < N ; i ++)
          if(pthreadarray[i] == tid)
              return i;
      return -1;
  }
  void *
  read_fn(void *arg)
  {
      pthread_t tid ;
      for(;;)
      {
          pthread_mutex_trylock(&rwlock);
          pthread_mutex_trylock(&rlock);
  
          readcount ++;
          if(readcount == 1)
              pthread_mutex_trylock(&wlock);
  
          tid = pthread_self();
          printf("\n****************************************************************\n \
                 now is read thread reading and the number is  %d ,tid is %ld\n \
                 the pool pos is %d and content is %d\n",find(tid),(long)tid,readpos,pool[readpos]);
  
          print();
          pool[readpos] = -1;
          readpos = (readpos+1)%N;
  
          readcount --;
          pthread_mutex_unlock(&rlock);
          if(readcount == 0)
              pthread_mutex_unlock(&wlock);
          pthread_mutex_unlock(&rwlock);
  
      }
  }
  void *
  write_fn(void *arg)
  {
      int val;
      pthread_t tid;
      for(;;)
      {
          pthread_mutex_trylock(&rwlock);
          pthread_mutex_trylock(&wlock);
  
          val = rand();
  
          tid = pthread_self();
          printf("\n****************************************************************\n \
                 now is write thread writing and the number is  %d ,tid is %ld\n \
                 the pool pos is %d and content is %d\n",find(tid),(long)tid,writepos,val);
  
          pool[writepos] = val;
          writepos = (writepos+1)%N;
  
          pthread_mutex_unlock(&wlock);
          pthread_mutex_unlock(&rwlock);
  
          print();
      }
  }
  
  void init()
  {
      int i;
      for(i = 0 ; i < 10 ; i ++)
          pool[i] = -1;
  }
  int main()
  {
      init();
  
      pthread_t thr1,thr2,thr3,thr4;
      int i = 0;
      srand((int)time(0));
  
      /* pthread_create(&thr1,NULL,write_fn,NULL);
       printf("the thread is wirte and  tid is %d\n",(int)thr1);
  
       pthread_create(&thr2,NULL,read_fn,NULL);
       printf("the thread is read and  tid is %d\n",(int)thr2);
  
       pthread_create(&thr3,NULL,read_fn,NULL);
       printf("the thread is read and  tid is %d\n",(int)thr3);
  
      pthread_create(&thr4,NULL,write_fn,NULL);
       printf("the thread is wirte and  tid is %d\n",(int)thr4);
      */
  
      for(i = 0 ; i < 10 ; i ++)
      {
          if(i%3 != 0)
          {
              pthread_create(&pthreadarray[i],NULL,write_fn,NULL);
              printf("start :the %d thread is wirte  and  tid is %ld\n",i,(long)pthreadarray[i]);
          }
          else
          {
              pthread_create(&pthreadarray[i],NULL,read_fn,NULL);
              printf("start :the %d thread is read and  tid is %ld\n",i,(long)pthreadarray[i]);
          }
  
      }
      sleep(10);
      exit(0);
  }

  参考：http://blog.csdn.net/lenic/article/details/4675142
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