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Diffstat (limited to 'lib/python2.7/bsddb/dbutils.py')
-rw-r--r-- | lib/python2.7/bsddb/dbutils.py | 83 |
1 files changed, 83 insertions, 0 deletions
diff --git a/lib/python2.7/bsddb/dbutils.py b/lib/python2.7/bsddb/dbutils.py new file mode 100644 index 0000000..02a686f --- /dev/null +++ b/lib/python2.7/bsddb/dbutils.py @@ -0,0 +1,83 @@ +#------------------------------------------------------------------------ +# +# Copyright (C) 2000 Autonomous Zone Industries +# +# License: This is free software. You may use this software for any +# purpose including modification/redistribution, so long as +# this header remains intact and that you do not claim any +# rights of ownership or authorship of this software. This +# software has been tested, but no warranty is expressed or +# implied. +# +# Author: Gregory P. Smith <greg@krypto.org> +# +# Note: I don't know how useful this is in reality since when a +# DBLockDeadlockError happens the current transaction is supposed to be +# aborted. If it doesn't then when the operation is attempted again +# the deadlock is still happening... +# --Robin +# +#------------------------------------------------------------------------ + + +# +# import the time.sleep function in a namespace safe way to allow +# "from bsddb.dbutils import *" +# +from time import sleep as _sleep + +import sys +absolute_import = (sys.version_info[0] >= 3) +if absolute_import : + # Because this syntaxis is not valid before Python 2.5 + exec("from . import db") +else : + import db + +# always sleep at least N seconds between retrys +_deadlock_MinSleepTime = 1.0/128 +# never sleep more than N seconds between retrys +_deadlock_MaxSleepTime = 3.14159 + +# Assign a file object to this for a "sleeping" message to be written to it +# each retry +_deadlock_VerboseFile = None + + +def DeadlockWrap(function, *_args, **_kwargs): + """DeadlockWrap(function, *_args, **_kwargs) - automatically retries + function in case of a database deadlock. + + This is a function intended to be used to wrap database calls such + that they perform retrys with exponentially backing off sleeps in + between when a DBLockDeadlockError exception is raised. + + A 'max_retries' parameter may optionally be passed to prevent it + from retrying forever (in which case the exception will be reraised). + + d = DB(...) + d.open(...) + DeadlockWrap(d.put, "foo", data="bar") # set key "foo" to "bar" + """ + sleeptime = _deadlock_MinSleepTime + max_retries = _kwargs.get('max_retries', -1) + if 'max_retries' in _kwargs: + del _kwargs['max_retries'] + while True: + try: + return function(*_args, **_kwargs) + except db.DBLockDeadlockError: + if _deadlock_VerboseFile: + _deadlock_VerboseFile.write( + 'dbutils.DeadlockWrap: sleeping %1.3f\n' % sleeptime) + _sleep(sleeptime) + # exponential backoff in the sleep time + sleeptime *= 2 + if sleeptime > _deadlock_MaxSleepTime: + sleeptime = _deadlock_MaxSleepTime + max_retries -= 1 + if max_retries == -1: + raise + + +#------------------------------------------------------------------------ |