From: Thomas Adam <thomas@xteddy.org>
Date: Wed, 06 Oct 2010 22:41:11 GMT
Subject: Re: [PATCHv5 03/17] gitweb/lib - Very simple file based cache
Message-ID: <AANLkTinPCOfknoN4aO_EdPwKorRiM6NU6ep0z_nnNug8@mail.gmail.com>
In-Reply-To: <1286402526-13143-4-git-send-email-jnareb@gmail.com>

On 6 October 2010 23:01, Jakub Narebski <jnareb@gmail.com> wrote:
> +# creates get_depth() and set_depth($depth) etc. methods
> +foreach my $i (qw(depth root namespace)) {
> +       my $field = $i;
> +       no strict 'refs';

For each item, you'll set "no strict refs"?  This might be better off
outside the loop.  It's still scoped appropriately inside the
subroutine.

> +       my $file = $self->path_to_key($key);
> +       return undef unless (defined $file && -f $file);

PBP (Perl Best Practises) will tell you that explicitly returning
undef is discouraged -- "undef" should be reserved for those errors
you cannot handle, not ones you don't want to.

> +
> +       # Fast slurp, adapted from File::Slurp::read, with unnecessary options removed
> +       # via CHI::Driver::File (from CHI-0.33)
> +       my $buf = '';
> +       open my $read_fh, '<', $file
> +               or return undef;

Ditto.

> +       binmode $read_fh, ':raw';
> +
> +       my $size_left = -s $read_fh;
> +
> +       while ($size_left > 0) {
> +               my $read_cnt = sysread($read_fh, $buf, $size_left, length($buf));
> +               return undef unless defined $read_cnt;

Ditto.

> +               last if $read_cnt == 0;
> +               $size_left -= $read_cnt;
> +               #last if $size_left <= 0;
> +       }
> +
> +       close $read_fh
> +               or die "Couldn't close file '$file' opened for reading: $!";
> +       return $buf;
> +}

"use Carp;" would be more useful here, and hence croak() and confess().

> +sub store {
> +       my ($self, $key, $data) = @_;
> +
> +       my $dir;
> +       my $file = $self->path_to_key($key, \$dir);
> +       return undef unless (defined $file && defined $dir);

See above.

> +       # ensure that directory leading to cache file exists
> +       if (!-d $dir) {
> +               eval { mkpath($dir, 0, 0777); 1 }
> +                       or die "Couldn't create leading directory '$dir' (mkpath): $!";
> +       }

Why is this eval()ed?  It will still return false and set $! appropriately.

> +       # generate a temporary file
> +       my ($temp_fh, $tempname) = $self->_tempfile_to_path($file, $dir);
> +       chmod 0666, $tempname
> +               or warn "Couldn't change permissions to 0666 / -rw-rw-rw- for '$tempname': $!";
> +
> +       # Fast spew, adapted from File::Slurp::write, with unnecessary options removed
> +       # via CHI::Driver::File (from CHI-0.33)
> +       my $write_fh = $temp_fh;
> +       binmode $write_fh, ':raw';
> +
> +       my $size_left = length($data);
> +       my $offset = 0;
> +
> +       while ($size_left > 0) {
> +               my $write_cnt = syswrite($write_fh, $data, $size_left, $offset);
> +               return undef unless defined $write_cnt;

Again, with the undef.

> +               $size_left -= $write_cnt;
> +               $offset += $write_cnt; # == length($data);
> +       }
> +
> +       close $temp_fh
> +               or die "Couldn't close temporary file '$tempname' opened for writing: $!";
> +       rename($tempname, $file)
> +               or die "Couldn't rename temporary file '$tempname' to '$file': $!";
> +}
> +
> +# get size of an element associated with the $key (not the size of whole cache)
> +sub get_size {
> +       my ($self, $key) = @_;
> +
> +       my $path = $self->path_to_key($key)
> +               or return undef;

Again with the undef

> +       if (-f $path) {
> +               return -s $path;
> +       }
> +       return 0;
> +}
> +
> +# ......................................................................
> +# interface methods
> +
> +# Removing and expiring
> +
> +# $cache->remove($key)
> +#
> +# Remove the data associated with the $key from the cache.
> +sub remove {
> +       my ($self, $key) = @_;
> +
> +       my $file = $self->path_to_key($key)
> +               or return undef;
> +       return undef unless -f $file;

Again with the undef.

> +       unlink($file)
> +               or die "Couldn't remove file '$file': $!";
> +}
> +
> +# Getting and setting
> +
> +# $cache->set($key, $data);
> +#
> +# Associates $data with $key in the cache, overwriting any existing entry.
> +# Returns $data.
> +sub set {
> +       my ($self, $key, $data) = @_;
> +
> +       return unless (defined $key && defined $data);

return what?

> +       $self->store($key, $data);
> +
> +       return $data;
> +}
> +
> +# $data = $cache->get($key);
> +#
> +# Returns the data associated with $key.  If $key does not exist
> +# or has expired, returns undef.
> +sub get {
> +       my ($self, $key) = @_;
> +
> +       my $data = $self->fetch($key)
> +               or return undef;
> +
> +       return $data;
> +}
> +
> +# $data = $cache->compute($key, $code);
> +#
> +# Combines the get and set operations in a single call.  Attempts to
> +# get $key; if successful, returns the value.  Otherwise, calls $code
> +# and uses the return value as the new value for $key, which is then
> +# returned.
> +sub compute {
> +       my ($self, $key, $code) = @_;
> +
> +       my $data = $self->get($key);
> +       if (!defined $data) {
> +               $data = $code->($self, $key);
> +               $self->set($key, $data);
> +       }

Can you guarantee $code here?

unless( defined $code and ref $code eq 'CODE' )
{
        ....
}

Wouldn't it be easier to eval{} this and checj $@?

[...]

-- Thomas Adam