Basic shared memory program in C
- by nicopuri
Hi,
I want to make a basic chat application in C using Shared memory. I am working in Linux. The application consist in writing the client and the server can read, and if the server write the client can read the message.
I tried to do this, but I can't achieve the communication between client and server. The code is the following:
Server.c
int
main(int argc, char **argv)
{
char *msg;
static char buf[SIZE];
int n;
msg = getmem();
memset(msg, 0, SIZE);
initmutex();
while ( true )
{
if( (n = read(0, buf, sizeof buf)) 0 )
{
enter();
sprintf(msg, "%.*s", n, buf);
printf("Servidor escribe: %s", msg);
leave();
}else{
enter();
if ( strcmp(buf, msg) )
{
printf("Servidor lee: %s", msg);
strcpy(buf, msg);
}
leave();
sleep(1);
}
}
return 0;
}
Client.c
int
main(int argc, char **argv)
{
char *msg;
static char buf[SIZE-1];
int n;
msg = getmem();
initmutex();
while(true)
{
if ( (n = read(0, buf, sizeof buf)) 0 )
{
enter();
sprintf(msg, "%.*s", n, buf);
printf("Cliente escribe: %s", msg);
leave();
}else{
enter();
if ( strcmp(buf, msg) )
{
printf("Cliente lee: %s", msg);
strcpy(buf, msg);
}
leave();
sleep(1);
}
}
printf("Cliente termina\n");
return 0;
}
The shared memory module is the folowing:
#include "common.h"
void
fatal(char *s)
{
perror(s);
exit(1);
}
char *
getmem(void)
{
int fd;
char *mem;
if ( (fd = shm_open("/message", O_RDWR|O_CREAT, 0666)) == -1 )
fatal("sh_open");
ftruncate(fd, SIZE);
if ( !(mem = mmap(NULL, SIZE, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0)) )
fatal("mmap");
close(fd);
return mem;
}
static sem_t *sd;
void
initmutex(void)
{
if ( !(sd = sem_open("/mutex", O_RDWR|O_CREAT, 0666, 1)) )
fatal("sem_open");
}
void
enter(void)
{
sem_wait(sd);
}
void
leave(void)
{
sem_post(sd);
}
