Hi,
I want to make 2 simple programs communicate each other with shared memory.
The programs will share an 2D array. In the first program (intarr.c) i create an x[3][4] array which is:
1 2 3 4
5 6 7 8
9 10 11 12
and i call the second program (intarr2.c) with execvp(); giving it the segment id as an argument. The intarr2.c just print the array to the terminal.
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,
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)
Hi All,
How do I write into shared memory blocks using multiple threads? For example, I have created 50 threads to write into shared memory and 50 threads to read from shared memory.
I have already created a shared memory and I want to write into shared memory as follows:
... (0 Replies)
Hi Everyone,
#!/usr/bin/perl
use strict;
use warnings;
my @test=("a;b;qqq;c;d","a;b;ggg;c;d","a;b;qqq;c;d");
would like to split the @test array into two array:
@test1=(("a;b;qqq;c;d","a;b;qqq;c;d"); and @test2=("a;b;ggg;c;d");
means search for 3rd filed.
Thanks
find the... (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 NETBSD
shmget
SHMGET(2) BSD System Calls Manual SHMGET(2)NAME
shmget -- get shared memory segment
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <sys/shm.h>
int
shmget(key_t key, size_t size, int shmflg);
DESCRIPTION
shmget() returns the shared memory identifier associated with the key key.
A shared memory segment is created if either key is equal to IPC_PRIVATE, or key does not have a shared memory segment identifier associated
with it, and the IPC_CREAT bit is set in shmflg. If both the IPC_CREAT bit and the IPC_EXCL bit are set in shmflg, and key has a shared mem-
ory segment identifier associated with it already, the operation will fail.
If a new shared memory segment is created, the data structure associated with it (the shmid_ds structure, see shmctl(2)) is initialized as
follows:
o shm_perm.cuid and shm_perm.uid are set to the effective uid of the calling process.
o shm_perm.gid and shm_perm.cgid are set to the effective gid of the calling process.
o shm_perm.mode is set to the lower 9 bits of shmflg.
o shm_lpid, shm_nattch, shm_atime, and shm_dtime are set to 0.
o shm_ctime is set to the current time.
o shm_segsz is set to the value of size.
RETURN VALUES
Upon successful completion a positive shared memory segment identifier is returned. Otherwise, -1 is returned and the global variable errno
is set to indicate the error.
ERRORS
[EACCES] A shared memory segment is already associated with key and the caller has no permission to access it.
[EEXIST] Both IPC_CREAT and IPC_EXCL are set in shmflg, and a shared memory segment is already associated with key.
[EINVAL] No shared memory segment is to be created, and a shared memory segment exists for key, but the size of the segment associ-
ated with it is less than size, which is non-zero.
A shared memory segment is to be created, and size is less than the system imposed minimum, or greater than the system
imposed maximum (refer to the kern.ipc values in sysctl(7)).
[ENOENT] IPC_CREAT is not set in shmflg and no shared memory segment associated with key was found.
[ENOMEM] There is not enough memory left to create a shared memory segment of the requested size.
[ENOSPC] A new shared memory identifier could not be created because the system limit for the number of shared memory identifiers
has been reached.
SEE ALSO ipcrm(1), ipcs(1), mmap(2), shmat(2), shmctl(2), ftok(3), sysctl(7)STANDARDS
The shmget system call conforms to X/Open System Interfaces and Headers Issue 5 (``XSH5'').
HISTORY
Shared memory segments appeared in the first release of AT&T System V UNIX.
BSD October 27, 2008 BSD
12-03-2011
