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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 1.19 by root, Sat Apr 11 04:42:29 2009 UTC

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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 17
18=head1 DESCRIPTION 18=head1 DESCRIPTION
19 19
20This module implements so-called "guards". A guard is something (usually 20This module implements so-called "guards". A guard is something (usually
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34 34
35=cut 35=cut
36 36
37package Guard; 37package Guard;
38 38
39no warnings;
40
39BEGIN { 41BEGIN {
40 $VERSION = '0.1'; 42 $VERSION = '1.02';
41 @ISA = qw(Exporter); 43 @ISA = qw(Exporter);
42 @EXPORT = qw(guard scope_guard); 44 @EXPORT = qw(guard scope_guard);
43 45
44 require Exporter; 46 require Exporter;
45 47
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137can create multiple timers or other event watchers and only when the last 139can 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 140one 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 141not have to worry about catching all the places where you have to unlock
140the semaphore. 142the semaphore.
141 143
142=item Guard::cancel $guard 144=item $guard->cancel
143 145
144Calling this function will "disable" the guard object returned by the 146Calling this function will "disable" the guard object returned by the
145C<guard> function, i.e. it will free the BLOCK originally passed to 147C<guard> function, i.e. it will free the BLOCK originally passed to
146C<guard >and will arrange for the BLOCK not to be executed. 148C<guard >and will arrange for the BLOCK not to be executed.
147 149
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160all, they are usually used to clean up after such exceptions. However, if 162all, they are usually used to clean up after such exceptions. However, if
161something truly exceptional is happening, a guard block should be allowed 163something truly exceptional is happening, a guard block should be allowed
162to die. Also, programming errors are a large source of exceptions, and the 164to die. Also, programming errors are a large source of exceptions, and the
163programmer certainly wants to know about those. 165programmer certainly wants to know about those.
164 166
165Since in most cases, the block executing when the guard gets executes does 167Since in most cases, the block executing when the guard gets executed does
166not know or does not care about the guard blocks, it makes little sense to 168not know or does not care about the guard blocks, it makes little sense to
167let containing code handle the exception. 169let containing code handle the exception.
168 170
169Therefore, whenever a guard block throws an exception, it will be caught, 171Therefore, whenever a guard block throws an exception, it will be caught,
170and this module will call the code reference stored in C<$Guard::DIED> 172followed 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 173C<$@> set to the actual exception), which is similar to how most event
172event loops handle this case. 174loops handle this case.
173 175
174The default for C<$Guard::DIED> is to call C<warn "$@">. 176The default for C<$Guard::DIED> is to call C<warn "$@">.
175 177
176The C<$@> variable will be restored to its value before the guard call in 178The C<$@> variable will be restored to its value before the guard call in
177all cases, so guards will not disturb C<$@> in any way. 179all cases, so guards will not disturb C<$@> in any way.
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187=head1 THANKS 189=head1 THANKS
188 190
189Thanks to Marco Maisenhelder, who reminded me of the C<$Guard::DIED> 191Thanks to Marco Maisenhelder, who reminded me of the C<$Guard::DIED>
190solution to the problem of exceptions. 192solution to the problem of exceptions.
191 193
194=head1 SEE ALSO
195
196L<Scope::Guard> and L<Sub::ScopeFinalizer>, which actually implement
197dynamic, not scoped guards, and have a lot higher CPU, memory and typing
198overhead.
199
200L<Hook::Scope>, which has apparently never been finished and corrupts
201memory when used.
202
192=cut 203=cut
193 204

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