Shared Memory Arena (shm-arena) is an applicationprogramming interface (API) library and utilityprograms for inter-process shared memory. It usesa name space to access shared memory betweenunrelated (or related) processes and a dynamicallocator. Name strings are used in place ofunderlying virtual address numbers to accessshared memory. This is analogous to the way filenames, are used to access regular computer filesin place of the underlying inode numbers. Anunderlying allocator class uses a structuredshared memory arena file which will grow or shrinkautomatically as more segments are requested fromthe malloc-like calls, or destroyed from free-likecalls.
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)
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)
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)
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)
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 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)
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)
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)
IPC::SharedMem(3pm) Perl Programmers Reference Guide IPC::SharedMem(3pm)NAME
IPC::SharedMem - SysV Shared Memory IPC object class
SYNOPSIS
use IPC::SysV qw(IPC_PRIVATE S_IRUSR S_IWUSR);
use IPC::SharedMem;
$shm = IPC::SharedMem->new(IPC_PRIVATE, 8, S_IRWXU);
$shm->write(pack("S", 4711), 2, 2);
$data = $shm->read(0, 2);
$ds = $shm->stat;
$shm->remove;
DESCRIPTION
A class providing an object based interface to SysV IPC shared memory.
METHODS
new ( KEY , SIZE , FLAGS )
Creates a new shared memory segment associated with "KEY". A new segment is created if
o "KEY" is equal to "IPC_PRIVATE"
o "KEY" does not already have a shared memory segment associated with it, and "FLAGS & IPC_CREAT" is true.
On creation of a new shared memory segment "FLAGS" is used to set the permissions. Be careful not to set any flags that the Sys V IPC
implementation does not allow: in some systems setting execute bits makes the operations fail.
id Returns the shared memory identifier.
read ( POS, SIZE )
Read "SIZE" bytes from the shared memory segment at "POS". Returns the string read, or "undef" if there was an error. The return value
becomes tainted. See shmread.
write ( STRING, POS, SIZE )
Write "SIZE" bytes to the shared memory segment at "POS". Returns true if successful, or false if there is an error. See shmwrite.
remove
Remove the shared memory segment from the system or mark it as removed as long as any processes are still attached to it.
is_removed
Returns true if the shared memory segment has been removed or marked for removal.
stat
Returns an object of type "IPC::SharedMem::stat" which is a sub-class of "Class::Struct". It provides the following fields. For a
description of these fields see you system documentation.
uid
gid
cuid
cgid
mode
segsz
lpid
cpid
nattach
atime
dtime
ctime
attach ( [FLAG] )
Permanently attach to the shared memory segment. When a "IPC::SharedMem" object is attached, it will use memread and memwrite instead
of shmread and shmwrite for accessing the shared memory segment. Returns true if successful, or false on error. See shmat.
detach
Detach from the shared memory segment that previously has been attached to. Returns true if successful, or false on error. See shmdt.
addr
Returns the address of the shared memory that has been attached to in a format suitable for use with "pack('P')". Returns "undef" if
the shared memory has not been attached.
SEE ALSO
IPC::SysV, Class::Struct
AUTHORS
Marcus Holland-Moritz <mhx@cpan.org>
COPYRIGHT
Version 2.x, Copyright (C) 2007-2010, Marcus Holland-Moritz.
Version 1.x, Copyright (c) 1997, Graham Barr.
This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
perl v5.18.2 2014-01-06 IPC::SharedMem(3pm)