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 ULTRIX
semop
semop(2) System Calls Manual semop(2)Name
semop - semaphore operations
Syntax
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
int semop (semid, sops, nsops)
int semid;
struct sembuf *sops[];
int nsops;
Description
The system call is used to atomically perform an array of semaphore operations on the set of semaphores associated with the semaphore iden-
tifier specified by The sops is a pointer to the array of semaphore-operation structures. The nsops is the number of such structures in
the array. The contents of each structure includes the following members:
short sem_num; /* semaphore number */
short sem_op; /* semaphore operation */
short sem_flg; /* operation flags */
Each semaphore operation specified by sem_op is performed on the corresponding semaphore specified by and sem_num.
The sem_op specifies one of three semaphore operations as follows:
1. If sem_op is a negative integer, one of the following occurs:
o If semval is greater than or equal to the absolute value of sem_op, the absolute value of sem_op is subtracted from semval. For fur-
ther information, see Also, if (sem_flg & SEM_UNDO) is true, the absolute value of sem_op is added to the calling process's semadj
value for the specified semaphore. For further information, see
o If semval is less than the absolute value of sem_op and (sem_flg & IPC_NOWAIT) is true, returns immediately.
o If semval is less than the absolute value of sem_op and (sem_flg & IPC_NOWAIT ) is false, increments the semncnt associated with the
specified semaphore and suspend execution of the calling process until one of the following occurs:
o If the semval becomes greater than or equal to the absolute value of sem_op. When this occurs, the value of semncnt associated with
the specified semaphore is decremented, the absolute value of sem_op is subtracted from semval, and if (sem_flg & SEM_UNDO) is true,
the absolute value of sem_op is added to the calling process's semadj value for the specified semaphore.
The for which the calling process is awaiting action is removed from the system. For further information, see When this occurs, errno
is set equal to EIDRM, and a value of -1 is returned.
The calling process receives a signal that is to be caught. When this occurs, the value of semncnt associated with the specified semaphore
is decremented, and the calling process resumes execution in the manner prescribed in
2. If sem_op is a positive integer, the value of sem_op is added to semval and, if (sem_flg & SEM_UNDO) is true, the value of sem_op is
subtracted from the calling process's semadj value for the specified semaphore.
3. If sem_op is zero, one of the following occurs:
o If semval is zero, returns immediately.
o If semval is not equal to zero and (sem_flg & IPC_NOWAIT) is true, returns immediately.
o If semval is not equal to zero and (sem_flg & IPC_NOWAIT) is false, increments the semzcnt associated with the specified semaphore and
suspend execution of the calling process, until one of the following occurs:
The semval became zero, at which time the value of semzcnt associated with the specified semaphore is decremented.
The for which the calling process is awaiting action is removed from the system. When this occurs, errno is set equal to EIDRM, and a
value of -1 is returned.
The calling process receives a signal that is to be caught. When this occurs, the value of semzcnt associated with the specified semaphore
is decremented, and the calling process resumes execution in the manner prescribed in
Upon successful completion, the value of sempid for each semaphore specified in the array pointed to by sops is set equal to the process ID
of the calling process.
Return Values
Upon successful completion, a value of 0 is returned. Otherwise, a value of -1 is returned, and errno is set to indicate the error.
Diagnostics
The fails if any of the following is true for any of the semaphore operations specified by sops:
[EINVAL] The sempid is not a valid semaphore identifier.
[EFBIG] The sem_num is less than zero or greater than or equal to the number of semaphores in the set associated with
[E2BIG] The nsops is greater than the system-imposed maximum.
[EACCESS] Operation permission is denied to the calling process. For further information, see
[EAGAIN] The operation would result in suspension of the calling process, but (sem_flg & IPC_NOWAIT) is true.
[ENOSPC] The limit on the number of individual processes requesting an SEM_UNDO would be exceeded.
[EINVAL] The number of individual semaphores for which the calling process request a SEM_UNDO would exceed the limit.
[ERANGE] An operation would cause a semval to overflow the system-imposed limit.
[ERANGE] An operation would cause a semadj value to overflow the system-imposed limit.
[EFAULT] The sops points to an illegal address.
[EINTR] The returns due to the receipt of a signal.
[EIDRM] The has been removed from the system.
See Alsoexecve(2), exit(2), fork(2), semctl(2), semget(2), signal(3)semop(2)