I am having problem with semaphores. I am trying to protect line where process prints so that every process with print in proper order.This is the code..
I would like first process to print something then second and so on. But i am getting all process mixed up and not in proper order.I am getting something like this...
Can anyone point me in what i am doing wrong.I think output should print...
Dear Reader,
I'm in a multiprocess environment working with shared mem and semaphores as mutex.. The problem is -- If one of the process hooked up with the semaphore and accessing the shared mem, terminates abruptly ( or got killed ), other process which are in want of the semaphore are... (1 Reply)
Hi all,
I am using HP 10.20 on A 9000/785. My question is:
If I am the only person logged in as root at the moment, how many "semaphore proccesses" should I have?? Is it only one, or it is relevant to other system proccesses?
Here is what I get listing the current semaphores
# ipcs -sp... (1 Reply)
Hi there,
Could someone please confirm which POSIX semaphore routines should be used for a multiprocess (and not multithreaded) environment?
sys/sem.h definitely works. but the routines, semget, semctl, semop are pretty unwieldy. So, I am looking for an easier way out.
From the man pages... (2 Replies)
Hi Friends,
If i execute this command it comes back with 300 lines:
ipcs|grep cerebrus >>> i would like to clear the semaphores but ipcrm can remove one id at a time. is there a quicker way of removing semaphores maybe using awk?
Regards, (1 Reply)
been searching around on how to use an up and down function with semaphores but i can't find an example. i looked into using: "semop" but i have no idea how to use it. I have been able to declared the semaphores using semget and initializing them using semctl. (7 Replies)
Hello, first of all I apologize if this thread is not in the correct section of this forum, but this one just seemed the most appropriate.
The question I have does not concern Unix specifically, it applies to virtually any OS, however it is in Unix where I learned about this problem.
So, the... (8 Replies)
Hello,
Iam trying to implement the sleeping barber problem using semaphores and running on UNIX machine. Iam linking it to the thread libraries :
bash-2.03$ g++ sleepingBarber.cpp -lpthread -o sleeping
but when i execute it i get the following error:
bash-2.03$ sleeping
Starting Program... (4 Replies)
Hello,
I was doing an exercise of semaphores and shared memory, namely the barbers:
-B number of barbers
-S number of chairs
-C number of customers.
I have done already and I compiled the code, but when run I get an error segment. Can not be and it took several days.
If anyone sees the error... (2 Replies)
Hello Everybody,
I am building a server. this server contains some data. Clients may modify this data or read this data.
If a client is reading the data and at the same time another client is modifying the data then at this case the reading client may read some false data (some old mixed with... (1 Reply)
Hi,
Can somebody please explain me what semaphores are? there purpose? and there effects?
Thanks in advance:) (0 Replies)
Discussion started by: Laxxi
0 Replies
LEARN ABOUT CENTOS
sem.h
sem.h(3HEAD) Headers sem.h(3HEAD)NAME
sem.h, sem - semaphore facility
SYNOPSIS
#include <sys/sem.h>
DESCRIPTION
The <sys/sem.h> header defines the following constants and structures.
Semaphore operation flags:
SEM_UNDO Set up adjust on exit entry.
Command definitions for the semctl() function are provided as listed below. See semctl(2).
GETNCNT Get semncnt.
GETPID Get sempid.
GETVAL Get semval.
GETALL Get all cases of semval.
GETZCNT Get semzcnt.
SETVAL Set semval.
SETALL Set all cases of semval.
The semid_ds structure contains the following members:
struct ipc_perm sem_perm /* operation permission structure */
unsigned short sem_nsems /* number of semaphores in set */
time_t sem_otime /* last semop() time */
time_t sem_ctime /* last time changed by semctl() */
The pid_t, time_t, key_t, and size_t types are defined as described in <sys/types.h>. See types.h(3HEAD).
A semaphore is represented by an anonymous structure containing the following members:
unsigned short semval /* semaphore value */
pid_t sempid /* process ID of last operation */
unsigned short semncnt /* number of processes waiting for semval
/* to become greater than current value */
unsigned short semzcnt /* number of processes waiting for semval to become 0 */
The sembuf structure contains the following members:
unsigned short sem_num /* semaphore number */
short sem_op /* semaphore operation */
short sem_flg /* operation flags */
All of the symbols from <sys/ipc.h> are defined when this header is included. See ipc.h(3HEAD).
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Interface Stability |Standard |
+-----------------------------+-----------------------------+
SEE ALSO semctl(2), semget(2), semop(2), ipc.h(3HEAD), types.h(3HEAD), attributes(5), standards(5)SunOS 5.10 10 Sep 2004 sem.h(3HEAD)