Dear Reader,
Is is necessary to attach / dettach the shared memory segments for write operations , if more than one program is accessing same shared memory segments..
I have used semaphore mutex and still I'm getting segmentation fault when I write to the segment when other program is already... (1 Reply)
I am running HP-UX B.11.11.
I'm increasing a parameter for a database engine so that it uses more memory to buffer the disk drive (to speed up performance). I have over 5GB of memory not being used.
But when I try to start the DB with the increased buffer parameter I get told.
"Not... (1 Reply)
Hi all :confused: ,
I am new to unix.I have been asked to implement shared memory in user's mode.What does this mean?What is the difference it makes in kernel mode and in users mode?What are the advantages of this impemenation(user's mode)?
And also i would like to know why exactly shared... (0 Replies)
what i want to do is have an int that can been written into by 2 processes but my code doesn't seem to work.
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <sys/shm.h>
#include<stdio.h>
#define KEY1 (1492)
int main()
{
int shmid;
volatile int * addr;... (6 Replies)
hi,
this is the problem: i want to swap a linked list between 4 processes (unrelated), is there any way i can do that just by sending a pointer to a structure?
//example
typedef struct node
{
int x;
char c;
struct node *next;
} node;
or i should send the items ( x,c ) by... (9 Replies)
I need to create a shared library to access an in memory DB. The DB is not huge, but big enough to make it cumbersome to carry around in every single process using the shared library. Luckily, it is pretty static information, so I don't need to worry much about synchronizing the data between... (12 Replies)
I am writing a shared library in Linux (but compatible with other UNIXes) and I want to allow multiple instances to share a piece of memory -- 1 byte is enough. What's the "best" way to do this? I want to optimize for speed and portability.
Obviously, I'll have to worry about mutual exclusion. (0 Replies)
Hello.
I am new to this forum and I would like to ask for advice about low level POSIX programming.
I have to implement a POSIX compliant C shared library.
A file will have some variables and the shared library will have some functions which need those variables.
There is one special... (5 Replies)
Discussion started by: iamjag
5 Replies
LEARN ABOUT FREEBSD
shmat
SHMAT(2) BSD System Calls Manual SHMAT(2)NAME
shmat, shmdt -- attach or detach shared memory
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
void *
shmat(int shmid, const void *addr, int flag);
int
shmdt(const void *addr);
DESCRIPTION
The shmat() system call attaches the shared memory segment identified by shmid to the calling process's address space. The address where the
segment is attached is determined as follows:
o If addr is 0, the segment is attached at an address selected by the kernel.
o If addr is nonzero and SHM_RND is not specified in flag, the segment is attached the specified address.
o If addr is specified and SHM_RND is specified, addr is rounded down to the nearest multiple of SHMLBA.
The shmdt() system call detaches the shared memory segment at the address specified by addr from the calling process's address space.
RETURN VALUES
Upon success, shmat() returns the address where the segment is attached; otherwise, -1 is returned and errno is set to indicate the error.
The shmdt() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate
the error.
ERRORS
The shmat() system call will fail if:
[EINVAL] No shared memory segment was found corresponding to shmid.
[EINVAL] The addr argument was not an acceptable address.
The shmdt() system call will fail if:
[EINVAL] The addr argument does not point to a shared memory segment.
SEE ALSO shmctl(2), shmget(2)BSD August 2, 1995 BSD