finding shared memory Post: 302326768

10 More Discussions You Might Find Interesting

1. Programming

Shared memory

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...

2. UNIX for Advanced & Expert Users

Shared memory shortage but lots of unused memory

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...

3. Linux

all about shared memory

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...

4. Programming

help with shared memory

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;...

5. Programming

memory sharing - not shared memory -

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...

6. Programming

Shared memory in shared library

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...

7. Programming

Shared memory for shared library

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.

8. AIX

shared memory

1.How to know wich process is using the shared memory? 2.How to flush (release) the process from the shared memory?

9. UNIX for Advanced & Expert Users

AIX: Finding processes attached to shared memory

Is there some way to tell what processes are attached to a shared memory segment? We have a system on which I perform "icps -ma" and there are several segments pending deletion having numerous processes attached to them and I can't tell what processes they are. Neither the creator's pid nor last...

10. Programming

Shared library with acces to shared memory.

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...

LEARN ABOUT OSX

shmdt

SHMAT(2)						      BSD System Calls Manual							  SHMAT(2)

NAME

     shmat, shmdt -- map/unmap shared memory

SYNOPSIS

     #include <sys/shm.h>

     void *
     shmat(int shmid, const void *shmaddr, int shmflg);

     int
     shmdt(const 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

     The shmat() system call will fail if:

     [EACCES]		The calling process has no permission to access this 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.

     [ENOMEM]		There is not enough available data space for the calling process to map the shared memory segment.

     The shmdt() system call will fail if:

     [EINVAL]		shmaddr is not the start address of a mapped shared memory segment.

LEGACY SYNOPSIS

     #include <sys/types.h>
     #include <sys/ipc.h>
     #include <sys/shm.h>

     The include files <sys/types.h> and <sys/ipc.h> are necessary for both functions.

SEE ALSO

     mmap(2), shmctl(2), shmget(2), compat(5)

BSD
								  August 17, 1995							       BSD