Programming

Hi
I need help regarding shared memory. I need to maintain the following structure in shared memory.

struct linked_list_header{
pid_t pid;
pthread_mutex_t lock;
int top;
int end;
int free;
NODE *ptr
}
The node structure is as follows
struct NODE {
int index;
int prv;
int nxt;
void *buffer;
}
Is it possible to maintain this dynamic linked_list_header in shared memory. I tried to maintain the same BUT I am not able to share the NODE structre data among the processes.

Thanks a lot

If you called malloc to create linked_list_header->ptr, then the address returned by malloc is private to the calling (the process that calls malloc) process. Same with NODE->buffer. You will have to allocate these things in shared "by hand" without calling malloc.

Thanks a Jim
I corrected my program to share the memory instead of malloc, Now it is working fine. I need another clarification regarding the same.

During run time, If I need more shared memory, Is it possible to mmap the increased size of dynamic memory while retaining the contents of previously mmaped memory. ( like realloc's functionality which preserves previously allocated memory contents)

Thanks once again

You mmap a second memory area. However mmap is not like malloc or realloc.
It works using pages of memory, not bytes. Create a really large memory block to start with. It sounds like you're using Linux.

Linux supports system V IPC XPG4.2 calls:

sys/shm.h provides support for shmat(), shmget(), etc.. You may also want to look at those calls.