Last touched file by a specific program ?

UNIX for Advanced & Expert Users
1

i have a directory where all .csv files are available. i have 3 perl programs(ex: a.pl,b.pl,c.pl) which continuously runs every 1 minute to scan all files in that directory. now i have 2 questions

1) how can i write an app lock on that particular folder to make sure only one program will scan that folder to get files so that other program will not catch same files ?

2) how to know if one perl program already touched a particular file ?
ex:
a.pl program scanned a folder and accessing 1.csv, 2.csv and 3.csv 3 files. Now it released app lock, now b.pl program accessing same folder but it should not read 1.csv, 2.csv and 3.csv files since a.pl already reading or accessed those folders.

Note: i don't want to rename any files in this process. How to do this ?

any help would be appreciated

2

Create a new file in that directory, that will be used as a lock file. Use flock - perldoc.perl.org on that lock file in all three scripts. Use that lock file to store information about which script executed last in this directory.

3

This would be one of the few examples the access time stamp could be sensibly used. Keep a.pl 's starting time stamp in the lock file proposed by bartus11; any file access since was by a.pl , any file accessed before can be processed by b.pl .

4

With respect to RudiC, use of a file's access time can be problematic if any other process reads the file, such as backups.

Why 3 programs? Are they three instances of the same program?

If the expense of starting a new process is not onerous, perhaps it would be easier just to use a dispatcher that launches no more than N of your programs:

(pseudo shell code!)

filescanner | while read file; do
  while [[ ${N} -le $(pgrep appropriateoptions | wc -l) ]]; sleep ${time}; done
  fileomatic ${file} &
done

Or the dispatcher could write a file to one of N named-pipes, one for each fileomatic, something like:

(more pseudo shell code)

work=$(mktemp -d)

N=0

while read fileomatic; do
  (( N = N + 1 ))
  pipe=${work}/pipe.${N}
  ready=${work}/ready.${N}

  mkfifo ${pipe}

  ${fileomatic} ${ready} < ${pipe} &
done 

filescanner | while read file; do

  while sleep ${delay}; do

    ls -1 ${work}/*.ready | read -aready

    if [[ 0 -lt ${#ready
[*]} ]]; then
      i=$(( ${RANDOM} % ${#ready
[*]} ))
      n=${ready[$i]}
      echo "${file}" >> ${work}/pipe.${n##*.}
      break
    fi

  done

done

The idea is that the fileomatic will touch the 'ready' file when it can process a file

5

Do you run them by crontab?
Then maybe you can simply chain them.

* * * * * a.pl; b.pl; c.pl