Login or Register to Ask a Question and Join Our Community

Sponsored Content
Full Discussion: Signals and semaphores
Top Forums Programming Signals and semaphores Post 302450782 by _thomas on Saturday 4th of September 2010 03:04:18 AM
Old 09-04-2010
I know I can do it like you suggested but I have more complicated case. I will try to explain my application more clearly.

I building communication gateway that connects two industrial networks (I have two network interfaces). I have two important threads. First thread is listening on Ethernet port 0 (eth0). This thread is basically a infinite loop that accepts incoming connections and messages send via GPRS protocol. When new message is received, it is processed by another thread. This new thread writes log files (for example) .

Second thread is listening on eth1. In most parts it is basically the same as first thread, but it can have just one client and another protocol is implemented.
Same as in first thread, when new message is received, it is processed by another thread. When message is received, response is send back right away
and my counter (they are counting from zero to timeout value) are reset.

If there is no new messages (timeout occurs) new thread is open (now from main program, before from signal handler) and message (required by protocol)
is send by another thread.

I have few variables that are shared between threads and main program. Counter is just one of them. Counter is different because it is incremented every second.

Before joining this forum I had sem_wait() before variable increment/decrement/reinitialization operation which was followed by sem_post(). I didn't put
semaphores if I was just testing logical expression. I've changed that.

I'm thinking of doing sem_post inside signal handler and sem_wait inside infitine while loop inside main(). This way code inside infinite loop will run once in
a second and tick variable will be threadsafe. All other shared variables will have sem_wait() -> operation -> sem_post(). Is this ok? I've attached below new pseudo code.

Code:
thread1() 
{
         sem_wait(semCounter)
         if(new_message_recieved)
               counter.t1 = 0;
         sem_post(semCounter);
}
 
void timer_handler(int signum) 
{     
       // counters are removed from signal_handler
       sem_post(semTick); 
}

int main()
{
      // Start timer
      // start main threads

      while(1)
      {
             
            sem_wait(semTick);
            // code bellow will be executed once in a second
            sem_wait(semCounter);
            counter.t1++;
            sem_post(semCounter);
       }
}

One more question about checking error code. If my sem_wait() is interruped by signal, it will return EINTR regardles of SA_RESTART flag. This way I could execute sem_wait() two times and sem_post just once.

Quote:
If a blocked call to one of the following interfaces is interrupted by a
signal handler, then the call will be automatically restarted after the signal
handler returns if the SA_RESTART flag was used; otherwise the call will fail
with the error EINTR:

* POSIX semaphore interfaces: sem_wait(3) and sem_timedwait(3) (since
Linux 2.6.22; beforehand, always failed with EINTR).
Last edited by _thomas; 09-04-2010 at 04:53 AM..
 

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

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

8. 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

9. Programming

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... (1 Reply)
Discussion started by: Omar_Mokhtar
1 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

LEARN ABOUT SUSE

pppoe-sniff

PPPOE-SNIFF(8)                                                System Manager's Manual                                               PPPOE-SNIFF(8)

NAME

       pppoe-sniff - examine network for non-standard PPPoE frames

SYNOPSIS

       pppoe-sniff [options]

DESCRIPTION

       pppoe-sniff listens for likely-looking PPPoE PADR and session frames and deduces extra options required for pppoe(8) to work.

       Some  DSL providers seem to use non-standard frame types for PPPoE frames, and/or require a certain value in the Service-Name field.  It is
       often easier to sniff those values from a machine which can successfully connect rather than try to pry them out of the DSL provider.

       To use pppoe-sniff, you need two computers, a DSL modem and an Ethernet hub (not an Ethernet switch.)

       If the DSL modem normally connects directly to your computer's Ethernet card, connect it to the "uplink" port on the  Ethernet  hub.   Plug
       two  computers into normal ports on the hub.  On one computer, run whatever software the DSL provider gave you on whatever operating system
       the DSL provider supports.  On the other computer, run Linux and log in as root.

       On the Linux machine, put the Ethernet interface into promiscuous mode and start pppoe-sniff.  If the ethernet interface is eth0, for exam-
       ple, type these commands:

            ifconfig eth0 promisc
            pppoe-sniff -I eth0

       On  the  other  machine, start your DSL connection as usual.  After a short time, pppoe-sniff should print recommendations for the value of
       PPPOE_EXTRA.  Set this value in /etc/ppp/pppoe.conf.  If pppoe-sniff indicates that something special is required in PPPOE_EXTRA, please e-
       mail this to pppoe@roaringpenguin.com along with the name of your ISP and the manufacturer and model number of your DSL modem.  This infor-
       mation will be collated and provided on the PPPoE web page for users who do not have two computers.

       After pppoe-sniff finishes (or you stop it if it seems hung), remember to turn off promiscuous mode:

            ifconfig eth0 -promisc

OPTIONS

       -I interface
              The -I option specifies the Ethernet interface to use.  Under Linux, it is typically eth0 or eth1.  The interface should be "up" and
              in promiscuous mode before you start pppoe-sniff.

       -V     The -V option causes pppoe-sniff to print its version number and exit.

BUGS

       pppoe-sniff only works on Linux.

AUTHORS

       pppoe-sniff was written by David F. Skoll <dfs@roaringpenguin.com>.

       The pppoe home page is http://www.roaringpenguin.com/pppoe/.

SEE ALSO

       pppd(8), pppoe(8), pppoe-sniff(8), pppoe-relay(8), /usr/share/doc/pppoe/README.Debian.gz

4th Berkeley Distribution                                           3 July 2000                                                     PPPOE-SNIFF(8)
All times are GMT -4. The time now is 11:45 PM.
Unix & Linux Forums Content Copyright 1993-2022. All Rights Reserved.
Privacy Policy