Perl::Critic::Policy::InputOutput::RequireBriefOpen - Close filehandles as soon as possible after opening them.
This Policy is part of the core Perl::Critic distribution.
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.
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
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.
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...
Initial development of this policy was supported by a grant from the Perl Foundation.
Chris Dolan <cdolan@cpan.org>
Copyright (c) 2007-2008 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