Shared memory is working only the first time [closed] - c++

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I am using shared memory to pass values between processes. It's working the first time, but when I try changing it again, the value is not getting reflected in other processes. First process A changes the value and signal B. It uses it and passes back the control to A. Then A again changes the value, but this new value is not getting reflected in process B.
// FILE 1
#include<stdio.h>
#include<sys/types.h>
#include<sys/socket.h>
#include<stdlib.h>
#include<unistd.h>
#include<string.h>
#include<arpa/inet.h>
#include<sys/time.h>
#include<iostream>
#include<netinet/in.h>
#include<sys/select.h>
#include<sys/shm.h>
#include<signal.h>
using namespace std;
struct shm
{
int aid;
int sid;
int bid;
int cid;
int portno;
int pno;
//int ports[4];
}*val;
int ports[4];
int sfds[4];
int count = 4;
void func1(int a)
{
fd_set rfds;
while (1)
{
FD_ZERO(&rfds);
struct timeval timer;
timer.tv_sec = 0;
timer.tv_usec = 10;
for (int i = 0; i < count; i++)
{
FD_SET(sfds[i], &rfds);
}
if (select(sfds[count - 1] + 1, &rfds, NULL, NULL, &timer))
{
for (int i = 0; i < count; i++)
{
if (FD_ISSET(sfds[i], &rfds))
{
val->pno = i;
val->portno = ports[i];
cout << "port number:" << val->portno << endl;
close(sfds[i]);
// Remove the corresponding sfd
for (int j = i; j < count - 1; j++)
{
sfds[j] = sfds[j + 1];
ports[j] = ports[j + 1];
}
count--;
kill(val->aid, SIGUSR2);
if (count > 0)
signal(SIGUSR1, &func1);
else
exit(1);
return;
}
}
}
}
}
void func2(int b)
{
struct sockaddr_in cliaddr;
socklen_t clilen;
int lc = 0;
for (int i = 0; i < 1; i++)
{
int nsfd = accept(sfds[val->pno], (struct sockaddr*) &cliaddr, &clilen);
if (nsfd < 0)
{
perror("Error");
exit(1);
}
cout << "Connection accepted";
send(nsfd, "OkaA", 5, 0);
close(nsfd);
}
if (close(sfds[val->pno]) < 0)
{
perror("Error closing");
exit(1);
}
cout << "Closed" << endl;
// Remove the corresponding sfd
for (int i = val->pno; i < count - 1; i++)
{
sfds[i] = sfds[i + 1];
ports[i] = ports[i + 1];
}
count--;
cout << " val->portnumber " << val->portno << endl;
kill(val->bid, SIGUSR1);
if (count > 0)
signal(SIGUSR2, &func2);
else
exit(1);
return;
}
int main()
{
int shmid = shmget(123456, sizeof(struct shm), IPC_CREAT | 0666);
if (shmid < 0)
{
perror("Error");
}
val = (struct shm*) shmat(shmid, NULL, 0);
//cout<<"yo2";
signal(SIGUSR1, &func1);
signal(SIGUSR2, &func2);
for (int i = 0; i < 4; i++)
{
//val->ports[i] = 7590+i;
sfds[i] = socket(AF_INET, SOCK_STREAM, 0);
const int optVal = 1;
const socklen_t optLen = sizeof(optVal);
int rtn = setsockopt(sfds[i], SOL_SOCKET, SO_REUSEADDR, (void*) &optVal,
optLen);
if (rtn < 0)
{
perror("Error");
exit(1);
}
struct sockaddr_in servaddr;
servaddr.sin_family = AF_INET;
servaddr.sin_port = htons(7590 + i);
ports[i] = i;
servaddr.sin_addr.s_addr = INADDR_ANY;
if (bind(sfds[i], (struct sockaddr*) &servaddr, sizeof(servaddr)) < 0)
{
perror("Error");
exit(1);
}
if (listen(sfds[i], 1) < 0)
{
perror("Error");
exit(1);
}
}
int c = fork();
if (c > 0)
{
val->aid = c;
val->sid = getpid();
kill(getpid(), SIGUSR1);
while (1)
;
}
else if (c == 0)
{
while (1)
;
}
else
{
perror("Error");
exit(1);
}
}
// FILE 2
#include<stdio.h>
#include<signal.h>
#include<sys/types.h>
#include<sys/socket.h>
#include<stdlib.h>
#include<unistd.h>
#include<string.h>
#include<arpa/inet.h>
#include<sys/time.h>
#include<iostream>
#include<netinet/in.h>
#include<sys/select.h>
#include<sys/shm.h>
using namespace std;
struct shm
{
int aid;
int sid;
int bid;
int cid;
int pno;
int portno;
}*val;
int sfds[4];
int count = 4;
void func1(int a)
{
int sfd = socket(AF_INET, SOCK_STREAM, 0);
struct sockaddr_in servaddr;
servaddr.sin_family = AF_INET;
servaddr.sin_port = htons(7590 + val->portno);
servaddr.sin_addr.s_addr = INADDR_ANY;
const int optVal = 1;
const socklen_t optLen = sizeof(optVal);
cout << val->portno << " vpn " << endl;
int rtn = setsockopt(sfd, SOL_SOCKET, SO_REUSEADDR, (void*) &optVal,
optLen);
while (bind(sfd, (struct sockaddr*) &servaddr, sizeof(servaddr)) < 0)
{
perror("Error");
}
cout << endl << "Done" << endl;
if (listen(sfd, 1) < 0)
{
perror("Error");
exit(1);
}
for (int i = 0; i < 1; i++)
{
struct sockaddr_in cliaddr;
socklen_t clilen;
int nsfd = accept(sfd, (struct sockaddr*) &cliaddr, &clilen);
send(nsfd, "OkaB", 5, 0);
}
close(sfd);
signal(SIGUSR1, &func1);
kill(val->cid, SIGUSR1);
}
int main()
{
signal(SIGUSR1, &func1);
int shmid = shmget(123456, sizeof(struct shm), IPC_CREAT | 0666);
if (shmid < 0)
{
perror("Error");
}
val = (struct shm*) shmat(shmid, NULL, 0);
val->bid = getpid();
while (1)
;
}

Answer 1

The problem may come from the struct shm definition:
In file 1
struct shm
{
int aid;
int sid;
int bid;
int cid;
int portno;
int pno;
//int ports[4];
}*val;
In other file :
struct shm
{
int aid;
int sid;
int bid;
int cid;
int pno;
int portno;
}*val;
pno and portno are not at the same place.
And as LPs pointed, only one process should create the shared memory (IPC_CREAT)