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Full Discussion: UNIX fifo concurrent read from a named pipe
Top Forums Shell Programming and Scripting UNIX fifo concurrent read from a named pipe Post 303013524 by Chubler_XL on Thursday 22nd of February 2018 04:41:46 PM
Old 02-22-2018
Probably best to use a mutex/semaphore to ensure only 1 process only reads from the pipe at a time.

I don't know what OS you are using so not sure if lockfile(1) is available to you.

This solution uses a lock directory as mkdir is supposed to be atomic:

readpipe.sh
Code:
lockdir=lock.dir

get_book() {
   local DONE=0
   while ! mkdir $lockdir 2> /dev/null
   do
      sleep 0.02
   done

   IFS="," read -u7 var || DONE=1

   rmdir $lockdir
   return $DONE
}

exec 7< namepipe
while get_book
do
   echo "$var" >> log$$.txt
done
exec 7<&-

Here is my test:

Code:
$ cat naveen 
mkfifo namepipe
./readpipe.sh &
./readpipe.sh &
exec 3<> namepipe
cat books.txt >&3
# Give time for readers to get established
sleep 1
# Close the write end
exec 3>&-
# wait for readers to complete
wait

$ ./naveen 

$ wc -l books.txt log*
 200 books.txt
 106 log2838.txt
  94 log2839.txt
 400 total

$ diff <(sort books.txt) <(cat log* | sort)


Update: below is an example using flock(1):

Code:
lockfile=lock.file

get_book() {
  var=$( (
      if flock -w .007 -n 200
      then
        IFS="," read -u7 var || exit 1
        echo "$var"
      fi) 200>$lockfile )
}

exec 7< namepipe

while get_book
do
  if [ -n "$var" ]
  then
          # Do any required work with the book record here...
          echo "$var" >> log$$.txt
  fi
done
exec 7<&-

Last edited by Chubler_XL; 02-25-2018 at 11:56 PM.. Reason: Added sleep to writer before close - avoid 1 process hogging the fifo
 

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ziparchive.addfile

ZIPARCHIVE.ADDFILE(3)							 1						     ZIPARCHIVE.ADDFILE(3)

ZipArchive::addFile - Adds a file to a ZIP archive from the given path

SYNOPSIS

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RETURN VALUES

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