Creating the log-file

dr_sad · 04-03-2005, 05:48 AM

Hi, all
I have written the socket program. It listen on the TCP port, receive the commands from the clients and make the system operations: add, delete and chpass users.
I have made it "daemon" and use fork() in it to serve more than one clients simultaneously.
Every child process write the log message to the log file /some/where/in/the/file/system/log.

How should I write to the file if the several process will be write to that file simultaneously?

Many thanx.
Sad Grablin.

P.S. sorry, i work in C.

Mara · 04-03-2005, 11:55 AM

Make one process that will deal with the log file and pass the messages to it using IPC routines. If you start with reading 'man msgsnd' you should understand how to do it fast.

dr_sad · 04-03-2005, 09:32 PM

Thank You, Mara, for your reply. I'll try to read 'man msgsnd'. But what about flock ? May it be useful?

Mara · 04-06-2005, 03:33 PM

You can also use locks, but I don't recommend it. It's easy to make the whole thing stop because of lock (when a number of processes wants to write and one is keeping the file. When using messages you don't need to deal with this problem.

Hko · 04-06-2005, 05:27 PM

Would semaphores be an option? (man semget)
And how would this compare to locks and message queues?

Mara · 04-12-2005, 05:01 PM

Locks lock files. In this case you may lock the log file. Message queues may be used to pass the data to be written to the log file to one process/thread from many others. Semaphores - if you have a semaphore that protects the log file (like lock, but at different level) and only teh thread that has it writes in, it will also work.