I think just do only a our write a code
Because Kernel is process management director and itself do it automatically..
For example let be we have two process and we share the same memory segment.
Firstly we use shmget() syscall for create memory portion
Code:
int shmget(key_t key, size_t size, int shmflg);
The key value in here "key" gives a identifier for memory portion "size" gives a shared memory size "shmflag" is used to choose "0700" .Because we want to create new memory portion..
If function success then return value gives to us "shared memory segment ID"..So Then return value from shmget gives shmid value..
For add to address space we use shmat()
Code:
void *shmat(int shmid,const *shmaddr,int shmflg);
let it be shmaddr = NULL -- > let the kernel choose a suitable address at which to attach the our shared mem segment portion.. shmflg = 0 --> because of NULL no neccessary set the flag
And then if shmat is successfull it returns shared mem segment address..
So we get the SHR address
Code:
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <unistd.h>
#include <sys/wait.h>
#define SHMSIZE 4096 /* 4K for shared mem segment */
int shmid, *shmptr ;
key_t mykey ;
mykey=123
shmid = shmget(mykey, SHM_SIZE, 0700 | IPC_CREAT) /* create shr mem segment */
shmptr = (int *) shmat(shmid, NULL, 0); /* attach segment mem to a pointer to it */
We create 4K SHR memory space..And we have a address pointer that called name shmptr..Then anyway we use it in our process (in c code..)
Hi All,
I'm facing the following issue with my shared libraries in AIX.
memory related calls such as memset, memcpy, malloc etc are failing miserably.
there is something wrong with stack/memory which i can't guess.
i've used the following flags to build my libraray:
ld -G... (0 Replies)
Using pmap, I was able to get a memory map of an Oracle process. It had the following id:
0000000380000000 4194320K rwxsR
Converting that Hex ID to decimal gave:
352321658
So, then I did ipcs -am:
IPC status from <running system> as of Thu Jun 18 15:43:17 MDT 2009
T ID ... (1 Reply)
Hello ,
I would like to know how to check if a given process id belongs to particualr shared memory segment .
Please help
Thanks in advance (3 Replies)
When I run 'top' command,I see the following
Memory: 32G real, 12G free, 96G swap free
Though it shows as 12G free,I am not able to account for processes that consume the rest 20G.
In my understanding some process should be consuming atleast 15-16 G but I am not able to find them.
Is... (1 Reply)
Hi again!
I have 2 questions ..:
How can i create exactly one number of processes ?
For example i want to create l*n processes and i tried this:
for(i=0;i<l*n;i++){
pid=fork()}
But it creates more than l*n
Also, i want each child to run another x.c program with 3 command line... (1 Reply)
Hi again!
I have 2 questions ..:
How can i create exactly one number of processes ?
For example i want to create l*n processes and i tried this:
for(i=0;i<l*n;i++){
pid=fork()}
But it creates more than l*n
Also, i want each child to run another x.c program with 3 command line... (1 Reply)
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)
Platform: Oracle Linux 6.4
To find the most memory consuming processes, I tried the following 2 methods
1. Method1
# ps aux | head -1 ; ps aux | sort -nk +4 | tail -7
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
root 95 0.0 0.0 0 0 ? ... (2 Replies)
Hi, i have 2 identical web servers using AIX. I use nmon analyser to check their performance.
The server A exceeds 20% memory usage for system, 5% for cache and the rest 75% for processes. While, it uses 4% of Paging Space.
The server B exceeds 20% for system, 45% for cache and 35% for processes.... (24 Replies)
Discussion started by: dim
24 Replies
LEARN ABOUT DEBIAN
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 <machine/param.h>
#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
05-06-2010
