perl and slow NFS

tmalyib has asked for the wisdom of the Perl Monks concerning the following question:

Monks, are there any good solutions for file access over a slow or busy NFS link? I have tried the following but I am not sure if it is the best solution.

sub checkfile {
 my $file = shift;
 my $duration = shift || 10;
 eval {
   local $SIG{ALRM} = sub { die "file access to $file failed\n" };

   alarm $duration;

   do {
     eval {
        die "cannot access $file\n" unless -e $file;
     };
     sleep 1 if $@;
   } until !$@;
   
   alarm 0;
 };

 return if $@;
 return 1 unless $@;
}
[download]

Comment on perl and slow NFS Download Code

Replies are listed 'Best First'.
Re: perl and slow NFS by wazoox (Prior) on Oct 18, 2007 at 14:40 UTC
NFS default behaviour is blocking IOs, that means the program accessing the share may eventually be frozen and can't be killed. I guess to circumvent this you need forking, accessing data from child, and waiting from father: `sub checkfile { my $file = shift; my $duration = shift \|\| 10; my $pid = fork(); unless ($pid) { # this is run from child die "cannot access $file\n" unless -e $file; } else { # this is run from parent sleep $duration; if ( kill 0, $pid) { warn "$pid still running after $duration seconds!"; kill 9, $pid; return; } return 1 } }` [download]	[reply] [d/l]

Replies are listed 'Best First'.

Re: perl and slow NFS
by wazoox (Prior) on Oct 18, 2007 at 14:40 UTC

sub checkfile {
    my $file = shift;
    my $duration = shift || 10;

    my $pid = fork();

    unless ($pid) {
        # this is run from child
        die "cannot access $file\n" unless -e $file;
  } else {
      # this is run from parent
    sleep $duration; 
    if ( kill 0, $pid) {
        warn "$pid still running after $duration seconds!";
        kill 9, $pid;
        return;
    }
    return 1
  }
}
[download]

[reply]
[d/l]