UNIX for Dummies Questions & Answers

Hi,
I am a Unix Newbie .

I want to write a program such a way that:
Whenever number of filedescriptors opened by a process change, it should execute some commands (eg: write total number of FDs at that point of time to a file).

I dont want to poll '/proc/<pid>/fd' at regular intervals (say 1min) because number of FDs change randomly.
If number of FDs change very frequently, then it will lead to inaccurate results if polling interval is large.
If number of FDs change very rarely (couple of changes per hr) , then it is waste to keep on polling.

So is there any other way to achieve my goal?
A psuedocode, sample shell script, C, Java prog, anything is OK for me.
Kindly help me in this..

Thanks in advance..

if you know ahead of time what directory tree(s) you are accessing then - if Linux - then inotify() will work just fine

inotifywatch will produce a report similar to what you are asking for as well.

You know, this sounds like you are trying to find out something and you decided that counting fd's was the answer. it may not be - what are you really doing?

Thanks Jim for your suggestion. I will have a look at inotify() function and try to implement desired logic.

What I was trying to do was:
I have a program on Solaris 9 OS platform, which opens a particular file for order processing (simulation). Rate at which orders are placed is random. Higher the rate, more instances of file are opened.
Currently, FD softlimit is 256(and they say this limit cant be increased more than this value for Solaris 9).
Whenever open FDs increase more than 256, orders fail. So I want to monitor total number of file descriptors. I hope inotify() will serve the purpose (if there is Solaris equivalent for this).

Solaris does not have inotify - a popen() call to fuser can do that for you. The best choice is to use the /proc directory via pfiles [pid]:
something like this --

Code:

#include <unistd.h>
#include <stdio.h>
#include <limits.h>
#include <stdlib.h>

int openfilecnt(void)
{
    int retval=0;
    FILE *cmd=NULL;
    char tmp[256]={0x0};
    char cmdstr[PATH_MAX+1]={0x0};
    sprintf(cmdstr, "/usr/bin/pfiles %d", getpid() );
    cmd=popen(cmdstr, "r");
    if(cmd==NULL) 
       { perror("command error"); exit(1);}
    while (fgets(tmp, sizeof(tmp), cmd)!=NULL)
    {
       retval++;
    }
    pclose(cmd);
    return (retval -2)/2;  
}

Next time. mention your OS, it helps a lot.