Advanced Programming in the UNIX® Environment

ptg10805159

940 Solutions to Selected Exercises Appendix C

int

clrasync(int sockfd)

{

int n;

n=0;

if (ioctl(sockfd, FIOASYNC, &n) < 0)

return(-1);

return(0);

}

Figure C.23 Enable and disable asynchronous socket I/O

Chapter 17

17.1 Regular pipes provide a byte stream interface. To detect message boundaries,

we’d have to add a header to each message to indicate the length. But this still

involves two extra copy operations: one to write to the pipe and one to read from

the pipe. Amoreefficient approach is to use the pipe only to signal the main

thread that a new message is available. We can use a single byte for this

purpose. With this approach, we need to move themymesgstructure to the

threadinfostructureand use a mutex and a condition variable to prevent the

helper thread from reusing themymesgstructureuntil the main thread is done

with it. The solution is shown in FigureC.24.

#include "apue.h"

#include <poll.h>

#include <pthread.h>

#include <sys/msg.h>

#include <sys/socket.h>

#define NQ 3/*number of queues */

#define MAXMSZ 512 /* maximum message size */

#define KEY 0x123 /* key for first message queue */

struct mymesg {

long mtype;

char mtext[MAXMSZ+1];

};

struct threadinfo {

int qid;

int fd;

int len;

pthread_mutex_t mutex;

pthread_cond_t ready;

struct mymesg m;

};