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 SUNOS
shmdt
shmop(2) System Calls shmop(2)NAME
shmop, shmat, shmdt - shared memory operations
SYNOPSIS
#include <sys/types.h>
#include <sys/shm.h>
void *shmat(int shmid, const void *shmaddr, int shmflg);
int shmdt(char *shmaddr);
Standard conforming
int shmdt(const void *shmaddr);
DESCRIPTION
The shmat() function attaches the shared memory segment associated with the shared memory identifier specified by shmid to the data segment
of the calling process.
The permission required for a shared memory control operation is given as {token}, where token is the type of permission needed. The types
of permission are interpreted as follows:
00400 READ by user
00200 WRITE by user
00040 READ by group
00020 WRITE by group
00004 READ by others
00002 WRITE by others
See the Shared Memory Operation Permissions section of intro(2) for more information.
When (shmflg&SHM_SHARE_MMU) is true, virtual memory resources in addition to shared memory itself are shared among processes that use the
same shared memory.
When (shmflg&SHM_PAGEABLE) is true, virtual memory resources are shared and the dynamic shared memory (DISM) framework is created. The
dynamic shared memory can be resized dynamically within the specified size in shmget(2). The DISM shared memory is pageable unless it is
locked.
The shared memory segment is attached to the data segment of the calling process at the address specified based on one of the following
criteria:
o If shmaddr is equal to (void *) 0, the segment is attached to the first available address as selected by the system.
o If shmaddr is equal to (void *) 0 and ( shmflg&SHM_SHARE_MMU) or (shmflg&SHM_PAGEABLE) is true, then the segment is attached to the
first available suitably aligned address. When (shmflg&SHM_SHARE_MMU) or (shmflg&SHM_PAGEABLE) is set, however, the permission given
by shmget() determines whether the segment is attached for reading or reading and writing.
o If shmaddr is not equal to (void *) 0 and (shmflg&SHM_RND) is true, the segment is attached to the address given by (shmaddr -
(shmaddr modulus SHMLBA)).
o If shmaddr is not equal to (void *) 0 and (shmflg&SHM_RND) is false, the segment is attached to the address given by shmaddr.
o The segment is attached for reading if (shmflg&SHM_RDONLY) is true {READ}, otherwise it is attached for reading and writing
{READ/WRITE}.
The shmdt() function detaches from the calling process's data segment the shared memory segment located at the address specified by
shmaddr. If the application is standard-conforming (see standards(5)), the shmaddr argument is of type const void *. Otherwise it is of
type char *.
Shared memory segments must be explicitly removed after the last reference to them has been removed.
RETURN VALUES
Upon successful completion, shmat() returns the data segment start address of the attached shared memory segment; shmdt() returns 0. Other-
wise, -1 is returned, the shared memory segment is not attached, and errno is set to indicate the error.
ERRORS
The shmat() function will fail if:
EACCES Operation permission is denied to the calling process (see intro(2)).
EINVAL The shmid argument is not a valid shared memory identifier.
EINVAL The shmaddr argument is not equal to 0, and the value of (shmaddr - (shmaddr modulus SHMLBA)) is an illegal address.
EINVAL The shmaddr argument is not equal to 0, is an illegal address, and (shmflg&SHM_RND) is false.
EINVAL The shmaddr argument is not equal to 0, is not properly aligned, and (shmfg&SHM_SHARE_MMU) is true.
EINVAL SHM_SHARE_MMU is not supported in certain architectures.
EINVAL Both (shmflg&SHM_SHARE_MMU) and (shmflg&SHM_PAGEABLE) are true.
EINVAL (shmflg&SHM_SHARE_MMU) is true and the shared memory segment specified by shmid() had previously been attached by a call to
shmat() in which (shmflg&SHM_PAGEABLE) was true.
(shmflg&SHM_PAGEABLE) is true and the shared memory segment specified by shmid() had previously been attached by a call to
shmat() in which (shmflg&SHM_SHARE_MMU) was true.
EMFILE The number of shared memory segments attached to the calling process would exceed the system-imposed limit.
ENOMEM The available data space is not large enough to accommodate the shared memory segment.
The shmdt() function will fail if:
EINVAL The shmaddr argument is not the data segment start address of a shared memory segment.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Interface Stability |Standard |
+-----------------------------+-----------------------------+
|MT-Level |Async-Signal-Safe |
+-----------------------------+-----------------------------+
SEE ALSO intro(2), exec(2), exit(2), fork(2), shmctl(2), shmget(2), standards(5)SunOS 5.10 1 Sep 2003 shmop(2)
05-06-2010
