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,
For some special reason , I'd like to control the memory address for the shared libraries in my dynamically linked process.
And it is the "ld" which interpret the dynamically linked library, and in my system, the "ld-linux.so.2" is put at 0x00812000. Then I use "prelink -r" command to change... (0 Replies)
hi,
For some special reason , I'd like to control the memory address for the shared libraries in my dynamically linked process.
And it is the "ld" which interpret the dynamically linked library, and in my system, the "ld-linux.so.2" is put at 0x00812000. Then I use "prelink -r" command to... (3 Replies)
Hi all,
I have been working on shared memory. I have created the shared memory and a linked list of 5 nodes. Now I want to attach the linked list to shared memory. When we attach a shared memory it returns a void pointer, but here I am in a fix , how to relate this void pointer to linked list.... (1 Reply)
Hi all,
I have been working on shared memory. I have created the shared memory and a linked list of 5 nodes. Now I want to attach the linked list to shared memory. When we attach a shared memory it returns a void pointer, but here I am in a fix , how to relate this void pointer to linked list.... (4 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)
I want to create a shared lib with certain libs statically linked to it. I can generate a fully shared lib as follows:
gcc -maix64 -DHAVE_CONFIG_H -I. -I./src -DHAVE_OPENSSL -I/usr/include/openssl -I/usr/include -I/usr/include/apr-1 -D_LARGEFILE64_SOURCE -I/usr/java8_64/include -shared -o... (0 Replies)
Discussion started by: amandeepgautam
0 Replies
LEARN ABOUT PLAN9
shm_overview
SHM_OVERVIEW(7) Linux Programmer's Manual SHM_OVERVIEW(7)NAME
shm_overview - overview of POSIX shared memory
DESCRIPTION
The POSIX shared memory API allows processes to communicate information by sharing a region of memory.
The interfaces employed in the API are:
shm_open(3) Create and open a new object, or open an existing object. This is analogous to open(2). The call returns a file descriptor
for use by the other interfaces listed below.
ftruncate(2) Set the size of the shared memory object. (A newly created shared memory object has a length of zero.)
mmap(2) Map the shared memory object into the virtual address space of the calling process.
munmap(2) Unmap the shared memory object from the virtual address space of the calling process.
shm_unlink(3) Remove a shared memory object name.
close(2) Close the file descriptor allocated by shm_open(3) when it is no longer needed.
fstat(2) Obtain a stat structure that describes the shared memory object. Among the information returned by this call are the
object's size (st_size), permissions (st_mode), owner (st_uid), and group (st_gid).
fchown(2) To change the ownership of a shared memory object.
fchmod(2) To change the permissions of a shared memory object.
Versions
POSIX shared memory is supported since Linux 2.4 and glibc 2.2.
Persistence
POSIX shared memory objects have kernel persistence: a shared memory object will exist until the system is shut down, or until all pro-
cesses have unmapped the object and it has been deleted with shm_unlink(3)
Linking
Programs using the POSIX shared memory API must be compiled with cc -lrt to link against the real-time library, librt.
Accessing shared memory objects via the filesystem
On Linux, shared memory objects are created in a (tmpfs(5)) virtual filesystem, normally mounted under /dev/shm. Since kernel 2.6.19,
Linux supports the use of access control lists (ACLs) to control the permissions of objects in the virtual filesystem.
NOTES
Typically, processes must synchronize their access to a shared memory object, using, for example, POSIX semaphores.
System V shared memory (shmget(2), shmop(2), etc.) is an older shared memory API. POSIX shared memory provides a simpler, and better
designed interface; on the other hand POSIX shared memory is somewhat less widely available (especially on older systems) than System V
shared memory.
SEE ALSO fchmod(2), fchown(2), fstat(2), ftruncate(2), mmap(2), mprotect(2), munmap(2), shmget(2), shmop(2), shm_open(3), shm_unlink(3), sem_over-
view(7)COLOPHON
This page is part of release 4.15 of the Linux man-pages project. A description of the project, information about reporting bugs, and the
latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.
Linux 2016-12-12 SHM_OVERVIEW(7)
06-25-2010
