Lib/bsddb/dbutils.py

   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 #
  27 from time import sleep as _sleep
  28
  29 import sys
  30 absolute_import = (sys.version_info[0] >= 3)
  31 if absolute_import :
  32     # Because this syntaxis is not valid before Python 2.5
  33     exec("from . import db")
  34 else :
  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
  47 def 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 'max_retries' in _kwargs:
  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 #------------------------------------------------------------------------