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#/usr/bin/env python
#
# Smart IO class
#
# Copyright (c) 2002 Red Hat, Inc.
#
# Author: Mihai Ibanescu <misa@redhat.com>
# $Id: SmartIO.py,v 1.1 2002/08/29 20:41:53 misa Exp $
"""
This module implements the SmartIO class
"""
import os
import time
from cStringIO import StringIO
class SmartIO:
"""
The SmartIO class allows one to put a cap on the memory consumption.
StringIO objects are very fast, because they are stored in memory, but
if they are too big the memory footprint becomes noticeable.
The write method of a SmartIO determines if the data that is to be added
to the (initially) StrintIO object does not exceed a certain threshold; if
it does, it switches the storage to a temporary disk file
"""
def __init__(self, max_mem_size=16384, force_mem=0):
self._max_mem_size = max_mem_size
self._io = StringIO()
# self._fixed is a flag to show if we're supposed to consider moving
# the StringIO object into a tempfile
# Invariant: if self._fixed == 0, we have a StringIO (if self._fixed
# is 1 and force_mem was 0, then we have a file)
if force_mem:
self._fixed = 1
else:
self._fixed = 0
def set_max_mem_size(self, max_mem_size):
self._max_mem_size = max_mem_size
def get_max_mem_size(self):
return self._max_mem_size
def write(self, data):
if not self._fixed:
# let's consider moving it to a file
if len(data) + self._io.tell() > self._max_mem_size:
# We'll overflow, change to a tempfile
tmpfile = _tempfile()
tmpfile.write(self._io.getvalue())
self._fixed = 1
self._io = tmpfile
self._io.write(data)
def __getattr__(self, name):
return getattr(self._io, name)
# Creates a temporary file and passes back its file descriptor
def _tempfile(tmpdir='/tmp'):
# Try to create the file a couple of times
filename = "%s/_rhn_transports-%d" % (tmpdir, os.getpid())
for i in range(5):
try:
fd = os.open(filename, os.O_CREAT | os.O_RDWR | os.O_EXCL)
except OSError, e:
if e.errno == 17:
# File exists
filename = "%s-%.5f" % (filename, time.time() % 10)
continue
# Another error, raise it
raise
else:
break
else:
# Failed to get the temp file
raise IOError, "Could not create temporary file"
# To make sure it's a temp file, unlink it
os.unlink(filename)
# Convert the file descriptor into a stream
f = os.fdopen(fd, "wb+")
return f
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