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Comparing Guard/Guard.pm (file contents):
Revision 1.10 by root, Sat Dec 13 18:50:31 2008 UTC vs.
Revision 1.16 by root, Mon Dec 15 02:38:21 2008 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 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 $VERSION = '0.5';
41 @ISA = qw(Exporter); 43 @ISA = qw(Exporter);
42 @EXPORT = qw(guard scope_guard); 44 @EXPORT = qw(guard scope_guard);
43 45
44 require Exporter; 46 require Exporter;
45 47
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133 135
134The advantage of doing this with a guard instead of simply calling C<< 136The advantage of doing this with a guard instead of simply calling C<<
135$sem->down >> in the callback is that you can opt not to create the timer, 137$sem->down >> in the callback is that you can opt not to create the timer,
136or your code can throw an exception before it can create the timer, or you 138or your code can throw an exception before it can create the timer, or you
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. 140one gets executed will the lock be unlocked. Using the C<guard>, you do
141not have to worry about catching all the places where you have to unlock
142the semaphore.
139 143
140=item Guard::cancel $guard 144=item $guard->cancel
141 145
142Calling this function will "disable" the guard object returned by the 146Calling this function will "disable" the guard object returned by the
143C<guard> function, i.e. it will free the BLOCK originally passed to 147C<guard> function, i.e. it will free the BLOCK originally passed to
144C<guard >and will arrange for the BLOCK not to be executed. 148C<guard >and will arrange for the BLOCK not to be executed.
145 149
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158all, they are usually used to clean up after such exceptions. However, if 162all, they are usually used to clean up after such exceptions. However, if
159something truly exceptional is happening, a guard block should be allowed 163something truly exceptional is happening, a guard block should be allowed
160to die. Also, programming errors are a large source of exceptions, and the 164to die. Also, programming errors are a large source of exceptions, and the
161programmer certainly wants to know about those. 165programmer certainly wants to know about those.
162 166
163Since in most cases, the block executing when the guard gets executes does 167Since in most cases, the block executing when the guard gets executed does
164not know or does not care about the guard blocks, it makes little sense to 168not know or does not care about the guard blocks, it makes little sense to
165let containing code handle the exception. 169let containing code handle the exception.
166 170
167Therefore, whenever a guard block throws an exception, it will be caught, 171Therefore, whenever a guard block throws an exception, it will be caught,
168and this module will call the code reference stored in C<$Guard::DIED> 172followed by calling the code reference stored in C<$Guard::DIED> (with
169(with C<$@> set to the actual exception), which is similar to how most 173C<$@> set to the actual exception), which is similar to how most event
170event loops handle this case. 174loops handle this case.
175
176The default for C<$Guard::DIED> is to call C<warn "$@">.
177
178The C<$@> variable will be restored to its value before the guard call in
179all cases, so guards will not disturb C<$@> in any way.
171 180
172The code reference stored in C<$Guard::DIED> should not die (behaviour is 181The code reference stored in C<$Guard::DIED> should not die (behaviour is
173not guaranteed, but right now, the exception will simply be ignored). 182not guaranteed, but right now, the exception will simply be ignored).
174 183
175The default for C<$Guard::DIED> is to call C<warn "$@">.
176
177=head1 AUTHOR 184=head1 AUTHOR
178 185
179 Marc Lehmann <schmorp@schmorp.de> 186 Marc Lehmann <schmorp@schmorp.de>
180 http://home.schmorp.de/ 187 http://home.schmorp.de/
181 188
182=head1 THANKS 189=head1 THANKS
183 190
184Thanks to Marco Maisenhelder, who reminded me of the C<$Guard::DIED> 191Thanks to Marco Maisenhelder, who reminded me of the C<$Guard::DIED>
185solution to the problem of exceptions. 192solution to the problem of exceptions.
186 193
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
187=cut 203=cut
188 204

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