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# Copyright 2010 United States Government as represented by the
# Administrator of the National Aeronautics and Space Administration.
# All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License"); you may
# not use this file except in compliance with the License. You may obtain
# a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations
# under the License.
"""
System-level utilities and helper functions.
"""
import hashlib
import logging
import uuid
from oslo_concurrency import lockutils
from oslo_utils.secretutils import md5
try:
from eventlet import sleep
except ImportError:
from time import sleep
from glance_store.i18n import _
LOG = logging.getLogger(__name__)
synchronized = lockutils.synchronized_with_prefix('glance_store-')
def is_uuid_like(val):
"""Returns validation of a value as a UUID.
For our purposes, a UUID is a canonical form string:
aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa
"""
try:
return str(uuid.UUID(val)) == val
except (TypeError, ValueError, AttributeError):
return False
def chunkreadable(iter, chunk_size=65536):
"""
Wrap a readable iterator with a reader yielding chunks of
a preferred size, otherwise leave iterator unchanged.
:param iter: an iter which may also be readable
:param chunk_size: maximum size of chunk
"""
return chunkiter(iter, chunk_size) if hasattr(iter, 'read') else iter
def chunkiter(fp, chunk_size=65536):
"""
Return an iterator to a file-like obj which yields fixed size chunks
:param fp: a file-like object
:param chunk_size: maximum size of chunk
"""
while True:
chunk = fp.read(chunk_size)
if chunk:
yield chunk
else:
break
def cooperative_iter(iter):
"""
Return an iterator which schedules after each
iteration. This can prevent eventlet thread starvation.
:param iter: an iterator to wrap
"""
try:
for chunk in iter:
sleep(0)
yield chunk
except Exception as err:
msg = _("Error: cooperative_iter exception %s") % err
LOG.error(msg)
raise
def cooperative_read(fd):
"""
Wrap a file descriptor's read with a partial function which schedules
after each read. This can prevent eventlet thread starvation.
:param fd: a file descriptor to wrap
"""
def readfn(*args):
result = fd.read(*args)
sleep(0)
return result
return readfn
def get_hasher(hash_algo, usedforsecurity=True):
"""
Returns the required hasher, given the hashing algorithm.
This is primarily to ensure that the hash algorithm is correctly
chosen when executed on a FIPS enabled system
:param hash_algo: hash algorithm requested
:param usedforsecurity: whether the hashes are used in a security context
"""
if str(hash_algo) == 'md5':
return md5(usedforsecurity=usedforsecurity)
else:
return hashlib.new(str(hash_algo))
class CooperativeReader(object):
"""
An eventlet thread friendly class for reading in image data.
When accessing data either through the iterator or the read method
we perform a sleep to allow a co-operative yield. When there is more than
one image being uploaded/downloaded this prevents eventlet thread
starvation, ie allows all threads to be scheduled periodically rather than
having the same thread be continuously active.
"""
def __init__(self, fd):
"""
:param fd: Underlying image file object
"""
self.fd = fd
self.iterator = None
# NOTE(markwash): if the underlying supports read(), overwrite the
# default iterator-based implementation with cooperative_read which
# is more straightforward
if hasattr(fd, 'read'):
self.read = cooperative_read(fd)
def read(self, length=None):
"""Return the next chunk of the underlying iterator.
This is replaced with cooperative_read in __init__ if the underlying
fd already supports read().
"""
if self.iterator is None:
self.iterator = self.__iter__()
try:
return next(self.iterator)
except StopIteration:
return b''
def __iter__(self):
return cooperative_iter(self.fd.__iter__())
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