ch13.017_best

来自「Perl Best Practices the source code」· 017_BEST 代码 · 共 50 行

##############################################################################
##   Code fragment (Recommended) from Chapter 13 of "Perl Best Practices"   ##
##     Copyright (c) O'Reilly & Associates, 2005. All Rights Reserved.      ##
##  See: http://www.oreilly.com/pub/a/oreilly/ask_tim/2001/codepolicy.html  ##
##############################################################################


# Standard modules...
use strict;
use warnings;
use IO::Prompt;
use Carp;
use English qw( -no_match_vars );
use Data::Alias;
use Readonly;

Readonly my $MAX_TRIES => 3;
sub acquire_resource { croak 'No resources available'; }
sub fibonacci {
    my ($n) = @_;
    return 1 if $n < 2;
    return fibonacci($n-1) + fibonacci($n-2);
}
sub nap {
    sleep @_;
}
sub do_something_using {
    print "doing something, man!\n";
}
my $resource;
my $resource_id;

TRY:
for my $try (1..$MAX_TRIES) {
    # If resource successfully acquired, we're done...
    eval { 
        $resource = acquire_resource($resource_id);
        last TRY;
    };
 
    # Report non-recoverable failure if no more tries
    croak( $EVAL_ERROR ) if $try == $MAX_TRIES;
 
    # Otherwise, try again after an increasing randomized interval...
    nap( rand fibonacci($try) ); 
}
 
do_something_using($resource);