I am using Shared memory (POSIX), to share a FILE pointer(FILE * rt_file), but it's not getting file pointer at client end. Any suggestions please.
/*
* shm_msgserver.c
*
* Illustrates memory mapping and persistency, with POSIX objects.
* This process produces a message leaving it in a shared segment.
* The segment is mapped in a persistent object meant to be subsequently
* open by a shared memory "client".
*
*
* Created by Mij <mij@bitchx.it> on 27/08/05.
* Original source file available at http://mij.oltrelinux.com/devel/unixprg/
*
*/
#include <stdio.h>
/* shm_* stuff, and mmap() */
#include <sys/mman.h>
#include <sys/types.h>
/* exit() etc */
#include <unistd.h>
#include <fcntl.h>
#include <sys/stat.h>
/* for random() stuff */
#include <stdlib.h>
#include <time.h>
/* Posix IPC object name [system dependant] - see
http://mij.oltrelinux.com/devel/unixprg/index2.html#ipc__posix_objects */
#define SHMOBJ_PATH "/foo1423"
/* maximum length of the content of the message */
#define MAX_MSG_LENGTH 50
/* how many types of messages we recognize (fantasy) */
#define TYPES 8
/* message structure for messages in the shared segment */
struct msg_s {
int type;
char content[MAX_MSG_LENGTH];
FILE *pt;
};
int main(int argc, char *argv[]) {
int shmfd;
int shared_seg_size = (1 * sizeof(struct msg_s)); /* want shared segment capable of storing 1 message */
struct msg_s *shared_msg; /* the shared segment, and head of the messages list */
FILE *rt_file;
rt_file = fopen ("res","a+");
printf("rt_file : %s\n",rt_file);
/* creating the shared memory object -- shm_open() */
shmfd = shm_open(SHMOBJ_PATH, O_CREAT | O_EXCL | O_RDWR, S_IRWXU | S_IRWXG);
if (shmfd < 0) {
perror("In shm_open()");
exit(1);
}
fprintf(stderr, "Created shared memory object %s\n", SHMOBJ_PATH);
/* adjusting mapped file size (make room for the whole segment to map) -- ftruncate() */
ftruncate(shmfd, shared_seg_size);
/* requesting the shared segment -- mmap() */
shared_msg = (struct msg_s *)mmap(NULL, shared_seg_size, PROT_READ | PROT_WRITE, MAP_SHARED, shmfd, 0);
if (shared_msg == NULL) {
perror("In mmap()");
exit(1);
}
fprintf(stderr, "Shared memory segment allocated correctly (%d bytes).\n", shared_seg_size);
srandom(time(NULL));
/* producing a message on the shared segment */
shared_msg->type = random() % TYPES;
snprintf(shared_msg->content, MAX_MSG_LENGTH, "My message, type %d, num %ld", shared_msg->type, random());
shared_msg->pt = rt_file;
/* [uncomment if you wish] requesting the removal of the shm object -- shm_unlink() */
/*
if (shm_unlink(SHMOBJ_PATH) != 0) {
perror("In shm_unlink()");
exit(1);
}
*/
return 0;
}
Client Code
/*
* shm_msgclient.c
* http://mij.oltrelinux.com/devel/unixprg/#ipc__posix_shm
* Illustrates memory mapping and persistency, with POSIX objects.
* This process reads and displays a message left it in "memory segment
* image", a file been mapped from a memory segment.
*
*
* Created by Mij <mij@bitchx.it> on 27/08/05.
* Original source file available at http://mij.oltrelinux.com/devel/unixprg/
*
*/
#include <stdio.h>
/* exit() etc */
#include <unistd.h>
/* shm_* stuff, and mmap() */
#include <sys/mman.h>
#include <sys/types.h>
#include <fcntl.h>
#include <sys/stat.h>
/* for random() stuff */
#include <stdlib.h>
#include <time.h>
/* Posix IPC object name [system dependant] - see
http://mij.oltrelinux.com/devel/unixprg/index2.html#ipc__posix_objects */
#define SHMOBJ_PATH "/foo1423"
/* maximum length of the content of the message */
#define MAX_MSG_LENGTH 50
/* how many types of messages we recognize (fantasy) */
#define TYPES 8
/* message structure for messages in the shared segment */
struct msg_s {
int type;
char content[MAX_MSG_LENGTH];
FILE *pt;
};
int main(int argc, char *argv[]) {
int shmfd;
int shared_seg_size = (1 * sizeof(struct msg_s)); /* want shared segment capable of storing 1 message */
struct msg_s *shared_msg; /* the shared segment, and head of the messages list */
FILE *rt_file;
/* creating the shared memory object -- shm_open() */
shmfd = shm_open(SHMOBJ_PATH, O_RDWR, S_IRWXU | S_IRWXG);
if (shmfd < 0) {
perror("In shm_open()");
exit(1);
}
printf("Created shared memory object %s\n", SHMOBJ_PATH);
/* requesting the shared segment -- mmap() */
shared_msg = (struct msg_s *)mmap(NULL, shared_seg_size, PROT_READ | PROT_WRITE, MAP_SHARED, shmfd, 0);
if (shared_msg == NULL) {
perror("In mmap()");
exit(1);
}
printf("Shared memory segment allocated correctly (%d bytes).\n", shared_seg_size);
rt_file = shared_msg->pt;
printf("rt_file : %s\n",rt_file);
rt_file = fopen ("res","a+");
printf("rt_file : %s\n", rt_file);
char x[10]="ABCDEFGHIJ";
fwrite(x, sizeof(x[0]), sizeof(x)/sizeof(x[0]), rt_file);
printf("Message type is %d, content is: %s\n", shared_msg->type, shared_msg->content);
if(shm_unlink(SHMOBJ_PATH) == -1){
printf("%s is used by another Process\n",SHMOBJ_PATH);
}
else{
printf("Memory is freed\n");
}
return 0;
}
