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 OPENDARWIN
shmdt
SHMAT(2) BSD System Calls Manual SHMAT(2)NAME
shmat, shmdt -- map/unmap shared memory
SYNOPSIS
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
void *
shmat(int shmid, void *shmaddr, int shmflg);
int
shmdt(void *shmaddr);
DESCRIPTION
shmat() maps the shared memory segment associated with the shared memory identifier shmid into the address space of the calling process. The
address at which the segment is mapped is determined by the shmaddr parameter. If it is equal to 0, the system will pick an address itself.
Otherwise, an attempt is made to map the shared memory segment at the address shmaddr specifies. If SHM_RND is set in shmflg, the system will
round the address down to a multiple of SHMLBA bytes (SHMLBA is defined in <sys/shm.h> ). A shared memory segment can be mapped read-only by
specifying the SHM_RDONLY flag in shmflg. shmdt() unmaps the shared memory segment that is currently mapped at shmaddr from the calling
process' address space. shmaddr must be a value returned by a prior shmat() call. A shared memory segment will remain existant until it is
removed by a call to shmctl(2) with the IPC_RMID command.
RETURN VALUES
shmat() returns the address at which the shared memory segment has been mapped into the calling process' address space when successful,
shmdt() returns 0 on successful completion. Otherwise, a value of -1 is returned, and the global variable errno is set to indicate the error.
ERRORS
shmat() will fail if:
[EACCES] The calling process has no permission to access this shared memory segment.
[ENOMEM] There is not enough available data space for the calling process to map the shared memory segment.
[EINVAL] shmid is not a valid shared memory identifier. shmaddr specifies an illegal address.
[EMFILE] The number of shared memory segments has reached the system-wide limit.
shmdt() will fail if:
[EINVAL] shmaddr is not the start address of a mapped shared memory segment.
SEE ALSO shmctl(2), shmget(2), mmap(2)BSD August 17, 1995 BSD
05-06-2010
