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| 3 | Guard - safe cleanup blocks |
3 | Guard - safe cleanup blocks |
| 4 | |
4 | |
| 5 | =head1 SYNOPSIS |
5 | =head1 SYNOPSIS |
| 6 | |
6 | |
| 7 | use Guard; |
7 | use Guard; |
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8 | |
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9 | # temporarily chdir to "/etc" directory, but make sure |
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10 | # to go back to "/" no matter how myfun exits: |
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11 | sub dosomething { |
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12 | scope_guard { chdir "/" }; |
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13 | chdir "/etc"; |
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14 | |
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15 | call_function_that_might_die_or_other_fun_stuff; |
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16 | } |
| 8 | |
17 | |
| 9 | =head1 DESCRIPTION |
18 | =head1 DESCRIPTION |
| 10 | |
19 | |
| 11 | This module implements so-called "guards". A guard is something (usually |
20 | This module implements so-called "guards". A guard is something (usually |
| 12 | an object) that "guards" a resource, ensuring that it is cleaned up when |
21 | an object) that "guards" a resource, ensuring that it is cleaned up when |
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| 60 | die if $@; |
69 | die if $@; |
| 61 | |
70 | |
| 62 | Except it is much faster, and the whole thing gets executed even when the |
71 | Except it is much faster, and the whole thing gets executed even when the |
| 63 | BLOCK calls C<exit>, C<goto>, C<last> or escapes via other means. |
72 | BLOCK calls C<exit>, C<goto>, C<last> or escapes via other means. |
| 64 | |
73 | |
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74 | If multiple BLOCKs are registered to the same scope, they will be executed |
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75 | in reverse order. Stuff like C<local> is managed via the same mechanism, |
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76 | so variables C<local>ised after calling C<scope_guard> will be restored |
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77 | when the guard runs. |
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78 | |
| 65 | See B<EXCEPTIONS>, below, for an explanation of exception handling |
79 | See B<EXCEPTIONS>, below, for an explanation of exception handling |
| 66 | (C<die>) within guard blocks. |
80 | (C<die>) within guard blocks. |
| 67 | |
81 | |
| 68 | Example: Temporarily change the directory to F</etc> and make sure it's |
82 | Example: temporarily change the timezone for the current process, |
| 69 | set back to F</> when the function returns: |
83 | ensuring it will be reset when the C<if> scope is exited: |
| 70 | |
84 | |
| 71 | sub dosomething { |
85 | use Guard; |
| 72 | scope_guard { chdir "/" }; |
86 | use POSIX (); |
| 73 | chdir "/etc"; |
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| 74 | |
87 | |
| 75 | ... |
88 | if ($need_to_switch_tz) { |
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89 | # make sure we call tzset after $ENV{TZ} has been restored |
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90 | scope_guard { POSIX::tzset }; |
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91 | |
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92 | # localise after the scope_guard, so it gets undone in time |
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93 | local $ENV{TZ} = "Europe/London"; |
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94 | POSIX::tzset; |
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95 | |
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96 | # do something with the new timezone |
| 76 | } |
97 | } |
| 77 | |
98 | |
| 78 | =item my $guard = guard BLOCK |
99 | =item my $guard = guard BLOCK |
| 79 | |
100 | |
| 80 | Behaves the same as C<scope_guard>, except that instead of executing |
101 | Behaves the same as C<scope_guard>, except that instead of executing |
