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       EndCoend

  
  

  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 <stdlib.h>#include <stdlib.h>        /* for convenience */#include <stddef.h>        /* for offsetof */#include <string.h>        /* for convenience */#include <unistd.h>        /* for convenience */#include <signal.h>        /* for SIG_ERR */#include <time.h>#include <pthread.h>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我独立博客的地址 ：http://www.fuxiang90.me/?p=314 欢迎访问交流