I don't see how writing 10-11 bytes twelve times won't cause roughly as much clobbering as writing 130 bytes once, but I did the test anyway.

A new script, write2.pl, to include several mechanisms: 

#!/usr/bin/perl

use strict;
use warnings;
use autodie;

use Bench;
use Fcntl qw(:flock);

unless (@ARGV == 3) {
    die "Usage: $0 <method> <path> <str>\n";
}

my ($method, $file, $str) = @ARGV;

bench sub {
    if ($method eq 'print') {
        open my($fh), ">>", $file;
        for (1..100_000) {
            print $fh "$str: $_\n";
        }
        close $fh;
    } elsif ($method eq 'open+print+close') {
        for (1..100_000) {
            open my($fh), ">>", $file;
            print $fh "$str: $_\n";
            close $fh;
        }
    } elsif ($method eq 'seek+print') {
        open my($fh), ">>", $file;
        for (1..100_000) {
            seek $fh, 0, 2;
            print $fh "$str: $_\n";
        }
        close $fh;
    } elsif ($method eq 'flock+print') {
        open my($fh), ">>", $file;
        for (1..100_000) {
            flock $fh, LOCK_EX;
            print $fh "$str: $_\n";
            flock $fh, LOCK_UN;
        }
        close $fh;
    }
};

[download]

Here's what the lines that get written should look like for process number 1: 

0010010010010010010010010010010010010010010010010010010010010010010010
+01001001001001001001001001001001001001001001001001001001001001: 1
0010010010010010010010010010010010010010010010010010010010010010010010
+01001001001001001001001001001001001001001001001001001001001001: 2
...

[download]

For process number 2: 

0020020020020020020020020020020020020020020020020020020020020020020020
+02002002002002002002002002002002002002002002002002002002002002: 1
0020020020020020020020020020020020020020020020020020020020020020020020
+02002002002002002002002002002002002002002002002002002002002002: 2
...

[download]

$ for i in `seq -f "%03g" 1 100`;do ( ./write2.pl print log $i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$$i$i$i$i & );done

Clobbering. Each process finishes in +- 7-9 secs.

$ for i in `seq -f "%03g" 1 100`;do ( ./write2.pl open+print+close log $i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$$i$i$i$i & );done

No clobbering. Each process finishes in +- 75 secs.

$ for i in `seq -f "%03g" 1 100`;do ( ./write2.pl seek+print log $i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$$i$i$i$i & );done

No clobbering. Each process finishes in +- 30 secs.

$ for i in `seq -f "%03g" 1 100`;do ( ./write2.pl flock+print log $i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$i$$i$i$i$i & );done

No clobbering. Each process finishes in +- 450 secs.

I'm guessing that the flock+print is the safest and most portable, but performance gets worse as the number of concurrent writers gets larger. For now I'm leaning towards the safest method, but will look into other possibilities in the future. What I would like to know is how safe the other methods are (open+print+close and seek+print) in avoiding clobbering.

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

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