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Comparing Guard/Guard.pm (file contents):
Revision 1.12 by root, Sat Dec 13 18:53:30 2008 UTC vs.
Revision 1.21 by root, Sun Jul 19 05:44:10 2009 UTC

… …
10 # to go back to "/" no matter how myfun exits: 10 # to go back to "/" no matter how myfun exits:
11 sub myfun { 11 sub myfun {
12 scope_guard { chdir "/" }; 12 scope_guard { chdir "/" };
13 chdir "/etc"; 13 chdir "/etc";
14 14
15 call_function_that_might_die_or_other_fun_stuff; 15 code_that_might_die_or_does_other_fun_stuff;
16 } 16 }
17
18 # create an object that, when the last reference to it is gone,
19 # invokes the given codeblock:
20 my $guard = guard { print "destroyed!\n" };
21 undef $guard; # probably destroyed here
17 22
18=head1 DESCRIPTION 23=head1 DESCRIPTION
19 24
20This module implements so-called "guards". A guard is something (usually 25This module implements so-called "guards". A guard is something (usually
21an object) that "guards" a resource, ensuring that it is cleaned up when 26an object) that "guards" a resource, ensuring that it is cleaned up when
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34 39
35=cut 40=cut
36 41
37package Guard; 42package Guard;
38 43
44no warnings;
45
39BEGIN { 46BEGIN {
40 $VERSION = '0.1'; 47 $VERSION = '1.021';
41 @ISA = qw(Exporter); 48 @ISA = qw(Exporter);
42 @EXPORT = qw(guard scope_guard); 49 @EXPORT = qw(guard scope_guard);
43 50
44 require Exporter; 51 require Exporter;
45 52
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137can create multiple timers or other event watchers and only when the last 144can create multiple timers or other event watchers and only when the last
138one gets executed will the lock be unlocked. Using the C<guard>, you do 145one gets executed will the lock be unlocked. Using the C<guard>, you do
139not have to worry about catching all the places where you have to unlock 146not have to worry about catching all the places where you have to unlock
140the semaphore. 147the semaphore.
141 148
142=item Guard::cancel $guard 149=item $guard->cancel
143 150
144Calling this function will "disable" the guard object returned by the 151Calling this function will "disable" the guard object returned by the
145C<guard> function, i.e. it will free the BLOCK originally passed to 152C<guard> function, i.e. it will free the BLOCK originally passed to
146C<guard >and will arrange for the BLOCK not to be executed. 153C<guard >and will arrange for the BLOCK not to be executed.
147 154
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160all, they are usually used to clean up after such exceptions. However, if 167all, they are usually used to clean up after such exceptions. However, if
161something truly exceptional is happening, a guard block should be allowed 168something truly exceptional is happening, a guard block should be allowed
162to die. Also, programming errors are a large source of exceptions, and the 169to die. Also, programming errors are a large source of exceptions, and the
163programmer certainly wants to know about those. 170programmer certainly wants to know about those.
164 171
165Since in most cases, the block executing when the guard gets executes does 172Since in most cases, the block executing when the guard gets executed does
166not know or does not care about the guard blocks, it makes little sense to 173not know or does not care about the guard blocks, it makes little sense to
167let containing code handle the exception. 174let containing code handle the exception.
168 175
169Therefore, whenever a guard block throws an exception, it will be caught, 176Therefore, whenever a guard block throws an exception, it will be caught,
170and this module will call the code reference stored in C<$Guard::DIED> 177followed by calling the code reference stored in C<$Guard::DIED> (with
171(with C<$@> set to the actual exception), which is similar to how most 178C<$@> set to the actual exception), which is similar to how most event
172event loops handle this case. 179loops handle this case.
173 180
174The default for C<$Guard::DIED> is to call C<warn "$@">. 181The default for C<$Guard::DIED> is to call C<warn "$@">.
175 182
176The C<$@> variable will be restored to its value before the guard call in 183The C<$@> variable will be restored to its value before the guard call in
177all cases, so guards will not disturb C<$@> in any way. 184all cases, so guards will not disturb C<$@> in any way.
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187=head1 THANKS 194=head1 THANKS
188 195
189Thanks to Marco Maisenhelder, who reminded me of the C<$Guard::DIED> 196Thanks to Marco Maisenhelder, who reminded me of the C<$Guard::DIED>
190solution to the problem of exceptions. 197solution to the problem of exceptions.
191 198
199=head1 SEE ALSO
200
201L<Scope::Guard> and L<Sub::ScopeFinalizer>, which actually implement
202dynamic, not scoped guards, and have a lot higher CPU, memory and typing
203overhead.
204
205L<Hook::Scope>, which has apparently never been finished and corrupts
206memory when used.
207
192=cut 208=cut
193 209

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