Perl::Critic::Policy::UsPerl::Critic::Policy::InputOutput::RequireBriefOpen(3)NAMEPerl::Critic::Policy::InputOutput::RequireBriefOpen - Close filehandles
as soon as possible after opening them.
AFFILIATION
This Policy is part of the core Perl::Critic distribution.
DESCRIPTION
One way that production systems fail unexpectedly is by running out of
filehandles. Filehandles are a finite resource on every operating
system that I'm aware of, and running out of them is virtually
impossible to recover from. The solution is to not run out in the
first place. What causes programs to run out of filehandles? Usually,
it's leaks: you open a filehandle and forget to close it, or just wait
a really long time before closing it.
This problem is rarely exposed by test systems, because the tests
rarely run long enough or have enough load to hit the filehandle limit.
So, the best way to avoid the problem is 1) always close all
filehandles that you open and 2) close them as soon as is practical.
This policy takes note of calls to "open()" where there is no matching
"close()" call within "N" lines of code. If you really need to do a
lot of processing on an open filehandle, then you can move that
processing to another method like this:
sub process_data_file {
my ($self, $filename) = @_;
open my $fh, '<', $filename
or croak 'Failed to read datafile ' . $filename . '; ' . $OS_ERROR;
$self->_parse_input_data($fh);
close $fh;
return;
}
sub _parse_input_data {
my ($self, $fh) = @_;
while (my $line = <$fh>) {
...
}
return;
}
As a special case, this policy also allows code to return the
filehandle after the "open" instead of closing it. Just like the
close, however, that "return" has to be within the right number of
lines. From there, you're on your own to figure out whether the code
is promptly closing the filehandle.
The STDIN, STDOUT, and STDERR handles are exempt from this policy.
CONFIGURATION
This policy allows "close()" invocations to be up to "N" lines after
their corresponding "open()" calls, where "N" defaults to 9. You can
override this to set it to a different number with the "lines" setting.
To do this, put entries in a .perlcriticrc file like this:
[InputOutput::RequireBriefOpen]
lines = 5
CAVEATS
"IO::File->new"
This policy only looks for explicit "open" calls. It does not detect
calls to "CORE::open" or "IO::File->new" or the like.
Is it the right lexical?
We don't currently check for redeclared filehandles. So the following
code is false negative, for example, because the outer scoped
filehandle is not closed:
open my $fh, '<', $file1 or croak;
if (open my $fh, '<', $file2) {
print <$fh>;
close $fh;
}
This is a contrived example, but it isn't uncommon for people to use
$fh for the name of the filehandle every time. Perhaps it's time to
think of better variable names...
CREDITS
Initial development of this policy was supported by a grant from the
Perl Foundation.
AUTHOR
Chris Dolan <cdolan@cpan.org>
COPYRIGHT
Copyright (c) 2007-2011 Chris Dolan. Many rights reserved.
This program is free software; you can redistribute it and/or modify it
under the same terms as Perl itself. The full text of this license can
be found in the LICENSE file included with this module
perl v5.14.1Perl::Critic::Policy::InputOutput::RequireBriefOpen(3)
