Sponsored Content
Full Discussion: about Semaphores
Top Forums Programming about Semaphores Post 302540658 by Omar_Mokhtar on Thursday 21st of July 2011 09:39:28 AM
Old 07-21-2011
about Semaphores

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 some new). So i used Semaphores to solve this problem so when any one is reading or writing he stops if another one is reading or writing.
but there is a small problem. i just want to prevent a reader from reading if there is someone writing. and prevent a writer from writing if there is another one writing. but i don't want to prevent a reader from reading if there is someone is also reading ! ..

cases i want to prevent : a reader requests reading and another one is writing , a writer requests writing and another one is writing , a writer requests writing and another one is reading. but a reader requests reading and another one is reading i don't want to prevent it.

how can i manage this using semaphores or any other tool ?

Thanks in advance
 

10 More Discussions You Might Find Interesting

1. Programming

Semaphores

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)
Discussion started by: joseph_shibu
1 Replies

2. UNIX for Dummies Questions & Answers

Semaphores

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)
Discussion started by: guest100
1 Replies

3. Programming

semaphores

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)
Discussion started by: qntmteleporter
2 Replies

4. Shell Programming and Scripting

semaphores

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)
Discussion started by: kekanap
1 Replies

5. Programming

semaphores using up and down

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)
Discussion started by: ddx08
7 Replies

6. UNIX for Advanced & Expert Users

How many semaphores?

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)
Discussion started by: Watto86
8 Replies

7. Programming

Semaphores Urgent

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)
Discussion started by: mohit.choudhary
4 Replies

8. Programming

Problem with semaphores

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)
Discussion started by: ciudadwifi
2 Replies

9. UNIX for Dummies Questions & Answers

semaphores

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.. #include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <sys/ipc.h> #include <sys/sem.h> #include <sys/types.h> union... (3 Replies)
Discussion started by: joker40
3 Replies

10. Solaris

Semaphores

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
PIPE(2) 							System Calls Manual							   PIPE(2)

NAME
pipe - create an interprocess channel SYNOPSIS
#include <u.h> #include <libc.h> int pipe(int fd[2]) DESCRIPTION
Pipe creates a buffered channel for interprocess I/O communication. Two file descriptors are returned in fd. Data written to fd[1] is available for reading from fd[0] and data written to fd[0] is available for reading from fd[1]. After the pipe has been established, cooperating processes created by subsequent fork(2) calls may pass data through the pipe with read and write calls. The bytes placed on a pipe by one write are contiguous even if many processes are writing. Write boundaries are preserved: each read terminates when the read buffer is full or after reading the last byte of a write, whichever comes first. The number of bytes available to a read(2) is reported in the Length field returned by fstat or dirfstat on a pipe (see stat(2)). When all the data has been read from a pipe and the writer has closed the pipe or exited, read(2) will return 0 bytes. Writes to a pipe with no reader will generate a note sys: write on closed pipe. SOURCE
/sys/src/libc/9syscall SEE ALSO
intro(2), read(2), pipe(3) DIAGNOSTICS
Sets errstr. BUGS
If a read or a write of a pipe is interrupted, some unknown number of bytes may have been transferred. When a read from a pipe returns 0 bytes, it usually means end of file but is indistinguishable from reading the result of an explicit write of zero bytes. PIPE(2)
All times are GMT -4. The time now is 09:18 PM.
Unix & Linux Forums Content Copyright 1993-2022. All Rights Reserved.
Privacy Policy