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Top Forums UNIX for Beginners Questions & Answers UNIX Pipe -Exit when there are no bytes to read Post 303015542 by rbatte1 on Friday 6th of April 2018 12:54:05 PM
Old 04-06-2018
I will assume that you already made a pipe file with something like mknod /$PIPEDIR/nvpipe p however I would be concerned that you have no idea which thread is reading the (now) input at any time.

You might find that the first reading process locks up the pipe, I'm not sure. It might be more sensible to ignore the pipe altogether and do something more like this:-
  • Split metadata.csv into 30 roughly equal files
  • Fire off 30 processes that read a separate input file each to do whatever processing you need
If you can get the number of lines in your file, you should be able to get the require line-count like this:-
Code:
#!/bin/bash
threads=30                                            # How many threads you want to work with

all_lines=$(wc -l < metadata.csv)                     # Count all the lines in your full input file
req_lines=$(printf $all_lines / $threads +1 | bc      # Get the lines required in each split file
                                                      # Rules of BIDMAS apply so the 1 is added after the divide

split -ld $req_lines metadata.csv metadata.           # Note the trailing dot. This will generate $threads files
                                                      # of up to $req_lines each in the format metadata.nn
                                                      # so up to 100 threads if you choose
for split_file in metadata.??
do
   ( while IFS=',' read DIR1 DIR2
   do
     printf "Start at $(date)\n"
     ${COMPUSETBIN}/prg1.sh prg2.sh $DIR1 $DIR2
     printf "Ending at $(date)\n"
     printf "++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++\n"
   done < $split_file
done ) &

wait               #  All threads must complete before this script will exit


It's untested, but does it get you started a bit better?

Probably there are better ways to do this in a single awk. What does your prg1.sh & prg2.sh actually do?



Kind regards,
Robin
 

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IO::Pipe(3pm)						 Perl Programmers Reference Guide					     IO::Pipe(3pm)

NAME
IO::Pipe - supply object methods for pipes SYNOPSIS
use IO::Pipe; $pipe = IO::Pipe->new(); if($pid = fork()) { # Parent $pipe->reader(); while(<$pipe>) { ... } } elsif(defined $pid) { # Child $pipe->writer(); print $pipe ... } or $pipe = IO::Pipe->new(); $pipe->reader(qw(ls -l)); while(<$pipe>) { ... } DESCRIPTION
"IO::Pipe" provides an interface to creating pipes between processes. CONSTRUCTOR
new ( [READER, WRITER] ) Creates an "IO::Pipe", which is a reference to a newly created symbol (see the "Symbol" package). "IO::Pipe::new" optionally takes two arguments, which should be objects blessed into "IO::Handle", or a subclass thereof. These two objects will be used for the system call to "pipe". If no arguments are given then method "handles" is called on the new "IO::Pipe" object. These two handles are held in the array part of the GLOB until either "reader" or "writer" is called. METHODS
reader ([ARGS]) The object is re-blessed into a sub-class of "IO::Handle", and becomes a handle at the reading end of the pipe. If "ARGS" are given then "fork" is called and "ARGS" are passed to exec. writer ([ARGS]) The object is re-blessed into a sub-class of "IO::Handle", and becomes a handle at the writing end of the pipe. If "ARGS" are given then "fork" is called and "ARGS" are passed to exec. handles () This method is called during construction by "IO::Pipe::new" on the newly created "IO::Pipe" object. It returns an array of two objects blessed into "IO::Pipe::End", or a subclass thereof. SEE ALSO
IO::Handle AUTHOR
Graham Barr. Currently maintained by the Perl Porters. Please report all bugs to <perlbug@perl.org>. COPYRIGHT
Copyright (c) 1996-8 Graham Barr <gbarr@pobox.com>. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself. perl v5.16.2 2012-10-11 IO::Pipe(3pm)
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