ViewVC Help
View File | Revision Log | Show Annotations | Download File
/cvs/Guard/Guard.pm
(Generate patch)

Comparing Guard/Guard.pm (file contents):
Revision 1.8 by root, Sat Dec 13 18:47:40 2008 UTC vs.
Revision 1.13 by root, Sat Dec 13 19:14:58 2008 UTC

… …
2 2
3Guard - safe cleanup blocks 3Guard - safe cleanup blocks
4 4
5=head1 SYNOPSIS 5=head1 SYNOPSIS
6 6
7 use Guard; 7 use Guard;
8 8
9 # temporarily chdir to "/etc" directory, but make sure 9 # temporarily chdir to "/etc" directory, but make sure
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 call_function_that_might_die_or_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
21an object) that "guards" a resource, ensuring that it is cleaned up when 21an object) that "guards" a resource, ensuring that it is cleaned up when
… …
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
… …
107 109
108See the EXCEPTIONS section for an explanation of how exceptions 110See the EXCEPTIONS section for an explanation of how exceptions
109(i.e. C<die>) are handled inside guard blocks. 111(i.e. C<die>) are handled inside guard blocks.
110 112
111Example: acquire a Coro::Semaphore for a second by registering a 113Example: acquire a Coro::Semaphore for a second by registering a
112timer. The timer callback references the guard used to unlock it again. 114timer. The timer callback references the guard used to unlock it
115again. (Please ignore the fact that C<Coro::Semaphore> has a C<guard>
116method that does this already):
113 117
118 use Guard;
114 use AnyEvent; 119 use AnyEvent;
115 use Coro::Semaphore; 120 use Coro::Semaphore;
116 121
117 my $sem = new Coro::Semaphore; 122 my $sem = new Coro::Semaphore;
118 123
119 sub lock_1s { 124 sub lock_for_a_second {
120 $sem->down; 125 $sem->down;
121 my $guard = guard { $sem->up }; 126 my $guard = guard { $sem->up };
122 127
123 my $timer; 128 my $timer;
124 $timer = AnyEvent->timer (after => 1, sub { 129 $timer = AnyEvent->timer (after => 1, sub {
… …
130 135
131The advantage of doing this with a guard instead of simply calling C<< 136The advantage of doing this with a guard instead of simply calling C<<
132$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,
133or 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
134can 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
135one 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.
136 143
137=item Guard::cancel $guard 144=item $guard->cancel
138 145
139Calling this function will "disable" the guard object returned by the 146Calling this function will "disable" the guard object returned by the
140C<guard> function, i.e. it will free the BLOCK originally passed to 147C<guard> function, i.e. it will free the BLOCK originally passed to
141C<guard >and will arrange for the BLOCK not to be executed. 148C<guard >and will arrange for the BLOCK not to be executed.
142 149
… …
164Therefore, whenever a guard block throws an exception, it will be caught, 171Therefore, whenever a guard block throws an exception, it will be caught,
165and this module will call the code reference stored in C<$Guard::DIED> 172and this module will call the code reference stored in C<$Guard::DIED>
166(with C<$@> set to the actual exception), which is similar to how most 173(with C<$@> set to the actual exception), which is similar to how most
167event loops handle this case. 174event loops handle this case.
168 175
176The default for C<$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<$@> in any way.
180
169The code reference stored in C<$Guard::DIED> should not die (behaviour is 181The code reference stored in C<$Guard::DIED> should not die (behaviour is
170not guaranteed, but right now, the exception will simply be ignored). 182not guaranteed, but right now, the exception will simply be ignored).
171
172The default for C<$Guard::DIED> is to call C<warn "$@">.
173 183
174=head1 AUTHOR 184=head1 AUTHOR
175 185
176 Marc Lehmann <schmorp@schmorp.de> 186 Marc Lehmann <schmorp@schmorp.de>
177 http://home.schmorp.de/ 187 http://home.schmorp.de/

Diff Legend

– Removed lines
+ Added lines
< Changed lines
> Changed lines