1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
|
# Copyright (C) 2009 Canonical Ltd
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
"""Helpers for managing cleanup functions and the errors they might raise.
The usual way to run cleanup code in Python is::
try:
do_something()
finally:
cleanup_something()
However if both `do_something` and `cleanup_something` raise an exception
Python will forget the original exception and propagate the one from
cleanup_something. Unfortunately, this is almost always much less useful than
the original exception.
If you want to be certain that the first, and only the first, error is raised,
then use::
operation = OperationWithCleanups(lambda operation: do_something())
operation.add_cleanup(cleanup_something)
operation.run()
This is more inconvenient (because you need to make every try block a
function), but will ensure that the first error encountered is the one raised,
while also ensuring all cleanups are run. See OperationWithCleanups for more
details.
"""
from collections import deque
import sys
from bzrlib import (
debug,
trace,
)
def _log_cleanup_error(exc):
trace.mutter('Cleanup failed:')
trace.log_exception_quietly()
if 'cleanup' in debug.debug_flags:
trace.warning('bzr: warning: Cleanup failed: %s', exc)
def _run_cleanup(func, *args, **kwargs):
"""Run func(*args, **kwargs), logging but not propagating any error it
raises.
:returns: True if func raised no errors, else False.
"""
try:
func(*args, **kwargs)
except KeyboardInterrupt:
raise
except Exception, exc:
_log_cleanup_error(exc)
return False
return True
def _run_cleanups(funcs):
"""Run a series of cleanup functions."""
for func, args, kwargs in funcs:
_run_cleanup(func, *args, **kwargs)
class OperationWithCleanups(object):
"""A way to run some code with a dynamic cleanup list.
This provides a way to add cleanups while the function-with-cleanups is
running.
Typical use::
operation = OperationWithCleanups(some_func)
operation.run(args...)
where `some_func` is::
def some_func(operation, args, ...)
do_something()
operation.add_cleanup(something)
# etc
Note that the first argument passed to `some_func` will be the
OperationWithCleanups object.
"""
def __init__(self, func):
self.func = func
self.cleanups = deque()
def add_cleanup(self, cleanup_func, *args, **kwargs):
"""Add a cleanup to run.
Cleanups may be added at any time before or during the execution of
self.func. Cleanups will be executed in LIFO order.
"""
self.cleanups.appendleft((cleanup_func, args, kwargs))
def run(self, *args, **kwargs):
return _do_with_cleanups(
self.cleanups, self.func, self, *args, **kwargs)
def _do_with_cleanups(cleanup_funcs, func, *args, **kwargs):
"""Run `func`, then call all the cleanup_funcs.
All the cleanup_funcs are guaranteed to be run. The first exception raised
by func or any of the cleanup_funcs is the one that will be propagted by
this function (subsequent errors are caught and logged).
Conceptually similar to::
try:
return func(*args, **kwargs)
finally:
for cleanup, cargs, ckwargs in cleanup_funcs:
cleanup(*cargs, **ckwargs)
It avoids several problems with using try/finally directly:
* an exception from func will not be obscured by a subsequent exception
from a cleanup.
* an exception from a cleanup will not prevent other cleanups from
running (but the first exception encountered is still the one
propagated).
Unike `_run_cleanup`, `_do_with_cleanups` can propagate an exception from a
cleanup, but only if there is no exception from func.
"""
# As correct as Python 2.4 allows.
try:
result = func(*args, **kwargs)
except:
# We have an exception from func already, so suppress cleanup errors.
_run_cleanups(cleanup_funcs)
raise
else:
# No exception from func, so allow the first exception from
# cleanup_funcs to propagate if one occurs (but only after running all
# of them).
exc_info = None
for cleanup, c_args, c_kwargs in cleanup_funcs:
# XXX: Hmm, if KeyboardInterrupt arrives at exactly this line, we
# won't run all cleanups... perhaps we should temporarily install a
# SIGINT handler?
if exc_info is None:
try:
cleanup(*c_args, **c_kwargs)
except:
# This is the first cleanup to fail, so remember its
# details.
exc_info = sys.exc_info()
else:
# We already have an exception to propagate, so log any errors
# but don't propagate them.
_run_cleanup(cleanup, *c_args, **kwargs)
if exc_info is not None:
raise exc_info[0], exc_info[1], exc_info[2]
# No error, so we can return the result
return result
|