I have been coding in perl off/on for two years now and am fairly comfortable with it on Win32 systems. I recently aqcuired responsibility for some *NIX systems and while creating some sample code to teach file locking, i found that it did not work on any (AIX,Solaris) of them. Symptoms are exactly the same:

I cannot get sleep or select(undef,undef,undef,250) to work in the while loop; my cursor just sits idle and i do not see the prints to STDOUT that are coded in the loop .... as soon as I comment out sleep/select it works fine.

BTW - this same script works on Win32. 
#!/usr/bin/perl -w
use strict;
use Fcntl ':flock';

my $file = '/export/home/smchugh/lock_file.txt';

print FILE "\nI HAVE LOCKED YOU @ @{[scalar localtime]}\n";

open (FILE, ">>$file") || die "Couldn't open $file.\n";
flock(FILE, LOCK_EX | LOCK_NB) || die "Couldn't lock $file.\n";

seek(FILE,0,2);



my $loop_var = 0;

while (1) {

    print "File $file is locked." unless $loop_var;
        select(undef,undef,undef, 250);    
    print "." if $loop_var;
    $loop_var = 1;
}

[download]

Edit Masem 2002-02-19 - Changed title from "losing confidence..."

In reply to Problems with sleep/select in loops by Anonymous Monk

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