02-10-2009
A semaphore with a value of one will make a good mutex. The first process in gets to decrement the semaphore, every other process has to wait. And when its done it increments the semaphore, letting the next process decrement it and take over.
Some good examples of sysv semaphores
here.
8 More Discussions You Might Find Interesting
1. IP Networking
Is there any facility to filter/identify the data calls and voice calls coming throug modem?
OR
Can we get the data or voice calls information through a script(preferably C Kermit)? (0 Replies)
Discussion started by: pcsaji
0 Replies
2. UNIX Desktop Questions & Answers
Hi,
I'm new to UNIX system calls. Can someone share your knowledge as to how exactly system calls should be executed?
Can they be typed like commands such as mkdir on the terminal itself? Also, are there any websites which will show me an example of the output to expect when a system call like... (1 Reply)
Discussion started by: ilavenil
1 Replies
3. BSD
what is the functions and relationship between fork,exec,wait system calls
as i am a beginer just want the fundamentals. (1 Reply)
Discussion started by: sangramdas
1 Replies
4. UNIX for Dummies Questions & Answers
Hi all,
I am new here .
I want to know about system call in detail.
As system calls are also function .How system identifies it.:) (2 Replies)
Discussion started by: vishwasrao
2 Replies
5. Shell Programming and Scripting
hi, i'm a noob
i have a quuestion: is possible to call and run the bash script by c++ program?
if so, is it posible in grafic? specially Qt ?
thanks (8 Replies)
Discussion started by: 3.14.TR
8 Replies
6. UNIX for Dummies Questions & Answers
Hello,
how would i be able to call ps in C programming?
thanks,
---------- Post updated at 01:39 AM ---------- Previous update was at 01:31 AM ----------
here's the complete system call, ps -o pid -p %d, getpit() (2 Replies)
Discussion started by: l flipboi l
2 Replies
7. Solaris
Hi Solaris experts
How to predefine the DESTDIR in a Solaris package?
Thanks (1 Reply)
Discussion started by: ./hari.sh
1 Replies
8. SCO
Hello,
I wonder if anybody could help. I'm running SCO Xenix under Qemu on Xubuntu 16.04. I created a SYSV floppy image, but the files on it are poorly displayed when I mounted it under Xenix.
I tried to create and format this image under Ubuntu as well as under Xenix.
How could I create a... (6 Replies)
Discussion started by: Neelix
6 Replies
shmop(2) System Calls Manual shmop(2)
Name
shmop, shmat, shmdt - shared memory operations
Syntax
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
char *shmat (shmid, shmaddr, shmflg)
int shmid;
char *shmaddr;
int shmflg;
int shmdt (shmaddr)
char *shmaddr;
Description
The system call attaches the shared memory segment associated with the shared memory identifier specified by shmid to the data segment of
the calling process. The segment is attached at the address specified by one of the following criteria:
If shmaddr is equal to zero, the segment is attached at the first available address as selected by the system.
If shmaddr is not equal to zero and (shmflg & SHM_RND ) is true, the segment is attached at the address given by (shmaddr- (shmaddr modulus
SHMLBA )).
If shmaddr is not equal to zero and (shmflg & SHM_RND ) is false, the segment is attached at the address given by shmaddr.
The segment is attached for reading if (shmflg & SHM_RDONLY ) is true. Otherwise, it is attached for reading and writing.
The system call detaches from the calling process's data segment the shared memory segment located at the address specified by shmaddr.
Return Values
Upon successful completion, the return values are as follows:
o The system call returns the data segment start address of the attached shared memory segment.
o The system call returns a value of zero (0).
Otherwise, a value of -1 is returned, and errno is set to indicate the error.
Diagnostics
The system call fails and not attach the shared memory segment, if any of the following is true:
[EINVAL] The shmid is not a valid shared memory identifier.
[EACCES] Operation permission is denied to the calling process. For further information, see
[ENOMEM] The available data space is not large enough to accommodate the shared memory segment.
[EINVAL] The shmaddr is not equal to zero, and the value of (shmaddr- (shmaddr modulus SHMLBA )) is an illegal address.
[EINVAL] The shmaddr is not equal to zero, (shmflg & SHM_RND ) is false, and the value of shmaddr is an illegal address.
[EMFILE] The number of shared memory segments attached to the calling process would exceed the system imposed limit.
The fails and does not detach the shared memory segment if:
[EINVAL] The shmaddr is not the data segment start address of a shared memory segment.
See Also
execve(2), exit(2), fork(2), shmctl(2), shmget(2)
shmop(2)