Advanced Programming in the UNIX® Environment

ptg10805159

Appendix C Chapter 17 Solutions 941

void *

helper(void *arg)

{

int n;

struct threadinfo *tip = arg;

for(;;) {

memset(&tip->m, 0, sizeof(struct mymsg));

if ((n = msgrcv(tip->qid, &tip->m, MAXMSZ, 0,

MSG_NOERROR)) < 0)

err_sys("msgrcv error");

tip->len = n;

pthread_mutex_lock(&tip->mutex);

if (write(tip->fd, "a", sizeof(char)) < 0)

err_sys("write error");

pthread_cond_wait(&tip->ready, &tip->mutex);

pthread_mutex_unlock(&tip->mutex);

}

}

int

main()

{

char c;

int i, n, err;

int fd[2];

int qid[NQ];

struct pollfd pfd[NQ];

struct threadinfo ti[NQ];

pthread_t tid[NQ];

for (i = 0; i < NQ; i++) {

if ((qid[i] = msgget((KEY+i), IPC_CREAT|0666)) < 0)

err_sys("msgget error");

printf("queue ID %d is %d\n", i, qid[i]);

if (socketpair(AF_UNIX, SOCK_DGRAM, 0, fd) < 0)

err_sys("socketpair error");

pfd[i].fd = fd[0];

pfd[i].events = POLLIN;

ti[i].qid = qid[i];

ti[i].fd = fd[1];

if (pthread_cond_init(&ti[i].ready, NULL) != 0)

err_sys("pthread_cond_init error");

if (pthread_mutex_init(&ti[i].mutex, NULL) != 0)

err_sys("pthread_mutex_init error");

if ((err = pthread_create(&tid[i], NULL, helper,

&ti[i])) != 0)

err_exit(err, "pthread_create error");

}