Re^3: Safe to open+close for every write, without locking?

in reply to Re^2: Safe to open+close for every write, without locking?
in thread Safe to open+close for every write, without locking?

Here ya go:

#!/usr/bin/perl

open my $fh, '>>', '/tmp/out' or die "open: $!\n";

sub output {
    my ($id) = @_;
    my $line = sprintf "[%02d: my id is: %02d]\n", $id, $id; # 19 char
+s
    print $fh $line x 500;  # bigger than 8K, and $line straddles boun
+dary
    warn "$id: sleeping...\n";
    sleep 1;
    warn "$id: exiting\n";
    exit;
}

for (1..3) {
    sleep 1;
    warn "$_: spawning...\n";
    my $pid = fork();
    die "fork failed: $!\n" unless defined $pid;
    next if $pid;
    # child
    output($_);
}
sleep 5;
__END__
[download]

And here's the output:

$ rm -f /tmp/out
$ perl5160 /tmp/p1
1: spawning...
1: sleeping...
2: spawning...
1: exiting
2: sleeping...
3: spawning...
3: sleeping...
2: exiting
3: exiting
$ grep -v '^\[..: my id is: ..]$' /tmp/out
[02[03: my id is: 03]
: my id is: 03]
$
[download]

Dave.

Comment on Re^3: Safe to open+close for every write, without locking? Select or Download Code

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Re^4: Safe to open+close for every write, without locking? by sedusedan (Monk) on Dec 22, 2012 at 01:48 UTC
Hi Dave, Thanks for writing the script. I added a `seek($fh, 0, 2)` before `print $fh ...` and it still manages to overlap. So, flock() it is.	[reply] [d/l] [select]

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