The harddrive I/O for sure is an issue, but it shouldn't cause the script to be slower. If anything, at least it should be able to perform as well.

Sorry, but that simply is not the case.

The program below reads two large files:

02/02/2015 15:42 10,737,418,241 big.csv 02/02/2015 15:47 12,300,000,001 big.tsv

First concurrently and then sequentially. The timings after the __END__ token show that reading them concurrently takes 5 times longer than reading them sequentially.

#! perl -slw use strict; use threads; use Time::HiRes qw[ sleep time ]; sub worker { my( $file, $start ) = @_; open my $in, '<', $file or die $!; sleep 0.0001 while time() < $start; my $count = 0; ++$count while <$in>; my $stop = time; return sprintf "$file:[%u] %.9f", $count, $stop - $start; } my $start = time + 1; my @workers = map threads->create( \&worker, $_, $start ), @ARGV; print $_->join for @workers; for my $file (@ARGV) { open my $in, '<', $file or die $!; my( $start, $count ) = ( time(), 0 ); ++$count while <$in>; printf "$file:[%u] %.9f\n", $count, time()-$start; } __END__ [15:49:22.32] E:\test>c:piotest.pl big.csv big.tsv big.csv:[167772161] 407.047676086 big.tsv:[100000001] 417.717574120 big.csv:[167772161] 82.103285074 big.tsv:[100000001] 81.984734058

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In reply to Re^3: Using threads to process multiple files by BrowserUk
in thread Using threads to process multiple files by anli_

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