> - Will this shared memory be accessible to non rt-task ?
> - What's the simplest way to share information with a non rt-task ?
Shared memory are also accessible to non-rt tasks. Since user-space
realtime and non-realtime threads from the same process reside in the
same address space, the simplest way to share information from rt to
non-rt tasks is to create them as threads of the same process.
Ok, but I figure out that it's possible to share memory between
processes ? (rt and non rt?)
For the moment, i focus on sharing between two rt tasks, but in vain :(
I still have a ftruncate error (EBADF) when i launch two rt processes...
I explain :
I've tried the attached program. I've added a sleep(1) between mmap and
munmap. I launch this appli twice with
>> shm_test &
>> shm_test &
For the second one, I got "ftruncate: Invalid argument". Am I the only
one to have this problem ?
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <unistd.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/mman.h>
#define MAX_LEN 10000
struct region { /* Defines "structure" of shared memory */
int len;
char buf[MAX_LEN];
};
struct region *rptr;
int fd;
int main(int argc, const char *argv[])
{
int fd, status;
mlockall(MCL_CURRENT|MCL_FUTURE);
/* Create shared memory object and set its size */
fd = shm_open("/myregion", O_CREAT | O_RDWR, S_IRUSR | S_IWUSR);
if (fd == -1) {
perror("shm_open");
exit(EXIT_FAILURE);
}
if ((status = ftruncate(fd, sizeof(struct region))) == -1) {
/* Handle error */;
perror("ftruncate");
close(fd);
status = EXIT_FAILURE;
goto close_and_unlink;
}
/* Map shared memory object */
rptr = (struct region *) mmap(NULL,
sizeof(struct region),
PROT_READ | PROT_WRITE,
MAP_SHARED,
fd,
0);
if (rptr == MAP_FAILED) {
/* Handle error */;
perror("mmap");
status = EXIT_FAILURE;
goto close_and_unlink;
}
/* Now we can refer to mapped region using fields of rptr;
for example, rptr->len */
sleep(1);
munmap(rptr, sizeof(struct region));
close_and_unlink:
close(fd);
shm_unlink("/myregion");
return status;
}
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