7 FileCache - keep more files open than the system permits
15 use FileCache maxopen => 16;
17 cacheout $mode, $path;
22 $fh = cacheout $mode, $path;
29 The C<cacheout> function will make sure that there's a filehandle open
30 for reading or writing available as the pathname you give it. It
31 automatically closes and re-opens files if you exceed your system's
32 maximum number of file descriptors, or the suggested maximum I<maxopen>.
38 The 1-argument form of cacheout will open a file for writing (C<< '>' >>)
39 on it's first use, and appending (C<<< '>>' >>>) thereafter.
41 Returns EXPR on success for convenience. You may neglect the
42 return value and manipulate EXPR as the filehandle directly if you prefer.
44 =item cacheout MODE, EXPR
46 The 2-argument form of cacheout will use the supplied mode for the initial
47 and subsequent openings. Most valid modes for 3-argument C<open> are supported
48 namely; C<< '>' >>, C<< '+>' >>, C<< '<' >>, C<< '<+' >>, C<<< '>>' >>>,
49 C< '|-' > and C< '-|' >
51 To pass supplemental arguments to a program opened with C< '|-' > or C< '-|' >
52 append them to the command string as you would system EXPR.
54 Returns EXPR on success for convenience. You may neglect the
55 return value and manipulate EXPR as the filehandle directly if you prefer.
61 While it is permissible to C<close> a FileCache managed file,
62 do not do so if you are calling C<FileCache::cacheout> from a package other
63 than which it was imported, or with another module which overrides C<close>.
64 If you must, use C<FileCache::cacheout_close>.
66 Although FileCache can be used with piped opens ('-|' or '|-') doing so is
67 strongly discouraged. If FileCache finds it necessary to close and then reopen
68 a pipe, the command at the far end of the pipe will be reexecuted - the results
69 of performing IO on FileCache'd pipes is unlikely to be what you expect. The
70 ability to use FileCache on pipes may be removed in a future release.
72 FileCache does not store the current file offset if it finds it necessary to
73 close a file. When the file is reopened, the offset will be as specified by the
74 original C<open> file mode. This could be construed to be a bug.
76 The module functionality relies on symbolic references, so things will break
77 under 'use strict' unless 'no strict "refs"' is also specified.
81 F<sys/param.h> lies with its C<NOFILE> define on some systems,
82 so you may have to set I<maxopen> yourself.
91 # These are not C<my> for legacy reasons.
92 # Previous versions requested the user set $cacheout_maxopen by hand.
93 # Some authors fiddled with %saw to overcome the clobber on initial open.
94 use vars qw(%saw $cacheout_maxopen);
95 $cacheout_maxopen = 16;
98 our @EXPORT = qw[cacheout cacheout_close];
102 my $cacheout_seq = 0;
105 my ($pkg,%args) = @_;
107 # Use Exporter. %args are for us, not Exporter.
108 # Make sure to up export_to_level, or we will import into ourselves,
109 # rather than our calling package;
111 __PACKAGE__->export_to_level(1);
112 Exporter::import( $pkg );
114 # Truth is okay here because setting maxopen to 0 would be bad
115 return $cacheout_maxopen = $args{maxopen} if $args{maxopen};
117 # XXX This code is crazy. Why is it a one element foreach loop?
118 # Why is it using $param both as a filename and filehandle?
119 foreach my $param ( '/usr/include/sys/param.h' ){
120 if (open($param, '<', $param)) {
123 if( /^\s*#\s*define\s+NOFILE\s+(\d+)/ ){
124 $cacheout_maxopen = $1 - 4;
132 $cacheout_maxopen ||= 16;
135 # Open in their package.
137 return open(*{caller(1) . '::' . $_[1]}, $_[0], $_[1]) && $_[1];
140 # Close in their package.
142 # Short-circuit in case the filehandle disappeared
143 my $pkg = caller($_[1]||0);
144 defined fileno(*{$pkg . '::' . $_[0]}) &&
145 CORE::close(*{$pkg . '::' . $_[0]});
146 delete $isopen{$_[0]};
149 # But only this sub name is visible to them.
151 my($mode, $file, $class, $ret, $ref, $narg);
152 croak "Not enough arguments for cacheout" unless $narg = scalar @_;
153 croak "Too many arguments for cacheout" if $narg > 2;
156 ($file, $mode) = ($mode, $file) if $narg == 1;
157 croak "Invalid mode for cacheout" if $mode &&
158 ( $mode !~ /^\s*(?:>>|\+?>|\+?<|\|\-|)|\-\|\s*$/ );
161 if( $isopen{$file} && ($mode||'>') ne $isopen{$file}->[1] ){
162 &cacheout_close($file, 1);
165 if( $isopen{$file}) {
167 $isopen{$file}->[0]++;
170 if( scalar keys(%isopen) > $cacheout_maxopen -1 ) {
171 my @lru = sort{ $isopen{$a}->[0] <=> $isopen{$b}->[0] } keys(%isopen);
173 $isopen{$_}->[0] = $cacheout_seq++ for
174 splice(@lru, int($cacheout_maxopen / 3)||$cacheout_maxopen);
175 &cacheout_close($_, 1) for @lru;
179 $mode ||= $saw{$file} ? '>>' : ($saw{$file}=1, '>');
181 #XXX should we just return the value from cacheout_open, no croak?
182 $ret = cacheout_open($mode, $file) or croak("Can't create $file: $!");
184 $isopen{$file} = [++$cacheout_seq, $mode];