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# Copyright (C) 2005, 2006 by Canonical Ltd
# Written by Robert Collins <robert.collins@canonical.com>
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
"""Bzrlib specific gzip tunings. We plan to feed these to the upstream gzip."""
# make GzipFile faster:
import gzip
from gzip import U32, LOWU32, FEXTRA, FCOMMENT, FNAME, FHCRC
import sys
import struct
import zlib
# we want a \n preserved, break on \n only splitlines.
import bzrlib
__all__ = ["GzipFile"]
class GzipFile(gzip.GzipFile):
"""Knit tuned version of GzipFile.
This is based on the following lsprof stats:
python 2.4 stock GzipFile write:
58971 0 5644.3090 2721.4730 gzip:193(write)
+58971 0 1159.5530 1159.5530 +<built-in method compress>
+176913 0 987.0320 987.0320 +<len>
+58971 0 423.1450 423.1450 +<zlib.crc32>
+58971 0 353.1060 353.1060 +<method 'write' of 'cStringIO.
StringO' objects>
tuned GzipFile write:
58971 0 4477.2590 2103.1120 bzrlib.knit:1250(write)
+58971 0 1297.7620 1297.7620 +<built-in method compress>
+58971 0 406.2160 406.2160 +<zlib.crc32>
+58971 0 341.9020 341.9020 +<method 'write' of 'cStringIO.
StringO' objects>
+58971 0 328.2670 328.2670 +<len>
Yes, its only 1.6 seconds, but they add up.
"""
def _add_read_data(self, data):
# 4169 calls in 183
# temp var for len(data) and switch to +='s.
# 4169 in 139
len_data = len(data)
self.crc = zlib.crc32(data, self.crc)
self.extrabuf += data
self.extrasize += len_data
self.size += len_data
def _read(self, size=1024):
# various optimisations:
# reduces lsprof count from 2500 to
# 8337 calls in 1272, 365 internal
if self.fileobj is None:
raise EOFError, "Reached EOF"
if self._new_member:
# If the _new_member flag is set, we have to
# jump to the next member, if there is one.
#
# First, check if we're at the end of the file;
# if so, it's time to stop; no more members to read.
next_header_bytes = self.fileobj.read(10)
if next_header_bytes == '':
raise EOFError, "Reached EOF"
self._init_read()
self._read_gzip_header(next_header_bytes)
self.decompress = zlib.decompressobj(-zlib.MAX_WBITS)
self._new_member = False
# Read a chunk of data from the file
buf = self.fileobj.read(size)
# If the EOF has been reached, flush the decompression object
# and mark this object as finished.
if buf == "":
self._add_read_data(self.decompress.flush())
assert len(self.decompress.unused_data) >= 8, "what does flush do?"
self._gzip_tail = self.decompress.unused_data[0:8]
self._read_eof()
# tell the driving read() call we have stuffed all the data
# in self.extrabuf
raise EOFError, 'Reached EOF'
self._add_read_data(self.decompress.decompress(buf))
if self.decompress.unused_data != "":
# Ending case: we've come to the end of a member in the file,
# so seek back to the start of the data for the next member which
# is the length of the decompress objects unused data - the first
# 8 bytes for the end crc and size records.
#
# so seek back to the start of the unused data, finish up
# this member, and read a new gzip header.
# (The number of bytes to seek back is the length of the unused
# data, minus 8 because those 8 bytes are part of this member.
seek_length = len (self.decompress.unused_data) - 8
if seek_length > 0:
# we read too much data
self.fileobj.seek(-seek_length, 1)
self._gzip_tail = self.decompress.unused_data[0:8]
elif seek_length < 0:
# we haven't read enough to check the checksum.
assert -8 < seek_length, "too great a seek."
buf = self.fileobj.read(-seek_length)
self._gzip_tail = self.decompress.unused_data + buf
else:
self._gzip_tail = self.decompress.unused_data
# Check the CRC and file size, and set the flag so we read
# a new member on the next call
self._read_eof()
self._new_member = True
def _read_eof(self):
"""tuned to reduce function calls and eliminate file seeking:
pass 1:
reduces lsprof count from 800 to 288
4168 in 296
avoid U32 call by using struct format L
4168 in 200
"""
# We've read to the end of the file, so we should have 8 bytes of
# unused data in the decompressor. If we don't, there is a corrupt file.
# We use these 8 bytes to calculate the CRC and the recorded file size.
# We then check the that the computed CRC and size of the
# uncompressed data matches the stored values. Note that the size
# stored is the true file size mod 2**32.
assert len(self._gzip_tail) == 8, "gzip trailer is incorrect length."
crc32, isize = struct.unpack("<LL", self._gzip_tail)
# note that isize is unsigned - it can exceed 2GB
if crc32 != U32(self.crc):
raise IOError, "CRC check failed %d %d" % (crc32, U32(self.crc))
elif isize != LOWU32(self.size):
raise IOError, "Incorrect length of data produced"
def _read_gzip_header(self, bytes=None):
"""Supply bytes if the minimum header size is already read.
:param bytes: 10 bytes of header data.
"""
"""starting cost: 300 in 3998
15998 reads from 3998 calls
final cost 168
"""
if bytes is None:
bytes = self.fileobj.read(10)
magic = bytes[0:2]
if magic != '\037\213':
raise IOError, 'Not a gzipped file'
method = ord(bytes[2:3])
if method != 8:
raise IOError, 'Unknown compression method'
flag = ord(bytes[3:4])
# modtime = self.fileobj.read(4) (bytes [4:8])
# extraflag = self.fileobj.read(1) (bytes[8:9])
# os = self.fileobj.read(1) (bytes[9:10])
# self.fileobj.read(6)
if flag & FEXTRA:
# Read & discard the extra field, if present
xlen = ord(self.fileobj.read(1))
xlen = xlen + 256*ord(self.fileobj.read(1))
self.fileobj.read(xlen)
if flag & FNAME:
# Read and discard a null-terminated string containing the filename
while True:
s = self.fileobj.read(1)
if not s or s=='\000':
break
if flag & FCOMMENT:
# Read and discard a null-terminated string containing a comment
while True:
s = self.fileobj.read(1)
if not s or s=='\000':
break
if flag & FHCRC:
self.fileobj.read(2) # Read & discard the 16-bit header CRC
def readline(self, size=-1):
"""Tuned to remove buffer length calls in _unread and...
also removes multiple len(c) calls, inlines _unread,
total savings - lsprof 5800 to 5300
phase 2:
4168 calls in 2233
8176 calls to read() in 1684
changing the min chunk size to 200 halved all the cache misses
leading to a drop to:
4168 calls in 1977
4168 call to read() in 1646
- i.e. just reduced the function call overhead. May be worth
keeping.
"""
if size < 0: size = sys.maxint
bufs = []
readsize = min(200, size) # Read from the file in small chunks
while True:
if size == 0:
return "".join(bufs) # Return resulting line
# c is the chunk
c = self.read(readsize)
# number of bytes read
len_c = len(c)
i = c.find('\n')
if size is not None:
# We set i=size to break out of the loop under two
# conditions: 1) there's no newline, and the chunk is
# larger than size, or 2) there is a newline, but the
# resulting line would be longer than 'size'.
if i==-1 and len_c > size: i=size-1
elif size <= i: i = size -1
if i >= 0 or c == '':
# if i>= 0 we have a newline or have triggered the above
# if size is not None condition.
# if c == '' its EOF.
bufs.append(c[:i+1]) # Add portion of last chunk
# -- inlined self._unread --
## self._unread(c[i+1:], len_c - i) # Push back rest of chunk
self.extrabuf = c[i+1:] + self.extrabuf
self.extrasize = len_c - i + self.extrasize
self.offset -= len_c - i
# -- end inlined self._unread --
return ''.join(bufs) # Return resulting line
# Append chunk to list, decrease 'size',
bufs.append(c)
size = size - len_c
readsize = min(size, readsize * 2)
def readlines(self, sizehint=0):
# optimise to avoid all the buffer manipulation
# lsprof changed from:
# 4168 calls in 5472 with 32000 calls to readline()
# to :
# 4168 calls in 417.
# Negative numbers result in reading all the lines
if sizehint <= 0:
sizehint = -1
content = self.read(sizehint)
return bzrlib.osutils.split_lines(content)
def _unread(self, buf, len_buf=None):
"""tuned to remove unneeded len calls.
because this is such an inner routine in readline, and readline is
in many inner loops, this has been inlined into readline().
The len_buf parameter combined with the reduction in len calls dropped
the lsprof ms count for this routine on my test data from 800 to 200 -
a 75% saving.
"""
if len_buf is None:
len_buf = len(buf)
self.extrabuf = buf + self.extrabuf
self.extrasize = len_buf + self.extrasize
self.offset -= len_buf
def write(self, data):
if self.mode != gzip.WRITE:
import errno
raise IOError(errno.EBADF, "write() on read-only GzipFile object")
if self.fileobj is None:
raise ValueError, "write() on closed GzipFile object"
data_len = len(data)
if data_len > 0:
self.size = self.size + data_len
self.crc = zlib.crc32(data, self.crc)
self.fileobj.write( self.compress.compress(data) )
self.offset += data_len
def writelines(self, lines):
# profiling indicated a significant overhead
# calling write for each line.
# this batch call is a lot faster :).
# (4 seconds to 1 seconds for the sample upgrades I was testing).
self.write(''.join(lines))
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