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/Lib/bsddb/dbutils.py

http://unladen-swallow.googlecode.com/
Python | 83 lines | 40 code | 7 blank | 36 comment | 2 complexity | d3aa53c8f900355af501e1d582d251eb MD5 | raw file
 1#------------------------------------------------------------------------
 2#
 3# Copyright (C) 2000 Autonomous Zone Industries
 4#
 5# License:      This is free software.  You may use this software for any
 6#               purpose including modification/redistribution, so long as
 7#               this header remains intact and that you do not claim any
 8#               rights of ownership or authorship of this software.  This
 9#               software has been tested, but no warranty is expressed or
10#               implied.
11#
12# Author: Gregory P. Smith <greg@krypto.org>
13#
14# Note: I don't know how useful this is in reality since when a
15#       DBLockDeadlockError happens the current transaction is supposed to be
16#       aborted.  If it doesn't then when the operation is attempted again
17#       the deadlock is still happening...
18#       --Robin
19#
20#------------------------------------------------------------------------
21
22
23#
24# import the time.sleep function in a namespace safe way to allow
25# "from bsddb.dbutils import *"
26#
27from time import sleep as _sleep
28
29import sys
30absolute_import = (sys.version_info[0] >= 3)
31if absolute_import :
32    # Because this syntaxis is not valid before Python 2.5
33    exec("from . import db")
34else :
35    import db
36
37# always sleep at least N seconds between retrys
38_deadlock_MinSleepTime = 1.0/128
39# never sleep more than N seconds between retrys
40_deadlock_MaxSleepTime = 3.14159
41
42# Assign a file object to this for a "sleeping" message to be written to it
43# each retry
44_deadlock_VerboseFile = None
45
46
47def DeadlockWrap(function, *_args, **_kwargs):
48    """DeadlockWrap(function, *_args, **_kwargs) - automatically retries
49    function in case of a database deadlock.
50
51    This is a function intended to be used to wrap database calls such
52    that they perform retrys with exponentially backing off sleeps in
53    between when a DBLockDeadlockError exception is raised.
54
55    A 'max_retries' parameter may optionally be passed to prevent it
56    from retrying forever (in which case the exception will be reraised).
57
58        d = DB(...)
59        d.open(...)
60        DeadlockWrap(d.put, "foo", data="bar")  # set key "foo" to "bar"
61    """
62    sleeptime = _deadlock_MinSleepTime
63    max_retries = _kwargs.get('max_retries', -1)
64    if _kwargs.has_key('max_retries'):
65        del _kwargs['max_retries']
66    while True:
67        try:
68            return function(*_args, **_kwargs)
69        except db.DBLockDeadlockError:
70            if _deadlock_VerboseFile:
71                _deadlock_VerboseFile.write(
72                    'dbutils.DeadlockWrap: sleeping %1.3f\n' % sleeptime)
73            _sleep(sleeptime)
74            # exponential backoff in the sleep time
75            sleeptime *= 2
76            if sleeptime > _deadlock_MaxSleepTime:
77                sleeptime = _deadlock_MaxSleepTime
78            max_retries -= 1
79            if max_retries == -1:
80                raise
81
82
83#------------------------------------------------------------------------