1
# Copyright (C) 2005, 2006 Canonical Ltd
2
# Written by Robert Collins <robert.collins@canonical.com>
4
# This program is free software; you can redistribute it and/or modify
5
# it under the terms of the GNU General Public License as published by
6
# the Free Software Foundation; either version 2 of the License, or
7
# (at your option) any later version.
9
# This program is distributed in the hope that it will be useful,
10
# but WITHOUT ANY WARRANTY; without even the implied warranty of
11
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12
# GNU General Public License for more details.
14
# You should have received a copy of the GNU General Public License
15
# along with this program; if not, write to the Free Software
16
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
18
"""Bzrlib specific gzip tunings. We plan to feed these to the upstream gzip."""
20
from cStringIO import StringIO
22
# make GzipFile faster:
24
from gzip import FEXTRA, FCOMMENT, FNAME, FHCRC
29
# we want a \n preserved, break on \n only splitlines.
32
__all__ = ["GzipFile", "bytes_to_gzip"]
36
"""Return i as an unsigned integer, assuming it fits in 32 bits.
38
If it's >= 2GB when viewed as a 32-bit unsigned int, return a long.
46
"""Return the low-order 32 bits of an int, as a non-negative int."""
47
return i & 0xFFFFFFFFL
50
def bytes_to_gzip(bytes, factory=zlib.compressobj,
51
level=zlib.Z_DEFAULT_COMPRESSION, method=zlib.DEFLATED,
52
width=-zlib.MAX_WBITS, mem=zlib.DEF_MEM_LEVEL,
54
"""Create a gzip file containing bytes and return its content."""
56
'\037\213' # self.fileobj.write('\037\213') # magic header
57
'\010' # self.fileobj.write('\010') # compression method
58
# fname = self.filename[:-3]
62
'\x00' # self.fileobj.write(chr(flags))
63
'\0\0\0\0' # write32u(self.fileobj, long(time.time()))
64
'\002' # self.fileobj.write('\002')
65
'\377' # self.fileobj.write('\377')
67
'' # self.fileobj.write(fname + '\000')
69
# using a compressobj avoids a small header and trailer that the compress()
70
# utility function adds.
71
compress = factory(level, method, width, mem, 0)
72
result.append(compress.compress(bytes))
73
result.append(compress.flush())
74
result.append(struct.pack("<L", LOWU32(crc32(bytes))))
75
# size may exceed 2GB, or even 4GB
76
result.append(struct.pack("<L", LOWU32(len(bytes))))
77
return ''.join(result)
80
class GzipFile(gzip.GzipFile):
81
"""Knit tuned version of GzipFile.
83
This is based on the following lsprof stats:
84
python 2.4 stock GzipFile write:
85
58971 0 5644.3090 2721.4730 gzip:193(write)
86
+58971 0 1159.5530 1159.5530 +<built-in method compress>
87
+176913 0 987.0320 987.0320 +<len>
88
+58971 0 423.1450 423.1450 +<zlib.crc32>
89
+58971 0 353.1060 353.1060 +<method 'write' of 'cStringIO.
92
58971 0 4477.2590 2103.1120 bzrlib.knit:1250(write)
93
+58971 0 1297.7620 1297.7620 +<built-in method compress>
94
+58971 0 406.2160 406.2160 +<zlib.crc32>
95
+58971 0 341.9020 341.9020 +<method 'write' of 'cStringIO.
97
+58971 0 328.2670 328.2670 +<len>
100
Yes, its only 1.6 seconds, but they add up.
103
def _add_read_data(self, data):
105
# temp var for len(data) and switch to +='s.
108
self.crc = zlib.crc32(data, self.crc)
109
self.extrabuf += data
110
self.extrasize += len_data
111
self.size += len_data
113
def _write_gzip_header(self):
114
"""A tuned version of gzip._write_gzip_header
116
We have some extra constrains that plain Gzip does not.
117
1) We want to write the whole blob at once. rather than multiple
118
calls to fileobj.write().
119
2) We never have a filename
120
3) We don't care about the time
123
'\037\213' # self.fileobj.write('\037\213') # magic header
124
'\010' # self.fileobj.write('\010') # compression method
125
# fname = self.filename[:-3]
129
'\x00' # self.fileobj.write(chr(flags))
130
'\0\0\0\0' # write32u(self.fileobj, long(time.time()))
131
'\002' # self.fileobj.write('\002')
132
'\377' # self.fileobj.write('\377')
134
'' # self.fileobj.write(fname + '\000')
137
def _read(self, size=1024):
138
# various optimisations:
139
# reduces lsprof count from 2500 to
140
# 8337 calls in 1272, 365 internal
141
if self.fileobj is None:
142
raise EOFError, "Reached EOF"
145
# If the _new_member flag is set, we have to
146
# jump to the next member, if there is one.
148
# First, check if we're at the end of the file;
149
# if so, it's time to stop; no more members to read.
150
next_header_bytes = self.fileobj.read(10)
151
if next_header_bytes == '':
152
raise EOFError, "Reached EOF"
155
self._read_gzip_header(next_header_bytes)
156
self.decompress = zlib.decompressobj(-zlib.MAX_WBITS)
157
self._new_member = False
159
# Read a chunk of data from the file
160
buf = self.fileobj.read(size)
162
# If the EOF has been reached, flush the decompression object
163
# and mark this object as finished.
166
self._add_read_data(self.decompress.flush())
167
if len(self.decompress.unused_data) < 8:
168
raise AssertionError("what does flush do?")
169
self._gzip_tail = self.decompress.unused_data[0:8]
171
# tell the driving read() call we have stuffed all the data
173
raise EOFError, 'Reached EOF'
175
self._add_read_data(self.decompress.decompress(buf))
177
if self.decompress.unused_data != "":
178
# Ending case: we've come to the end of a member in the file,
179
# so seek back to the start of the data for the next member which
180
# is the length of the decompress objects unused data - the first
181
# 8 bytes for the end crc and size records.
183
# so seek back to the start of the unused data, finish up
184
# this member, and read a new gzip header.
185
# (The number of bytes to seek back is the length of the unused
186
# data, minus 8 because those 8 bytes are part of this member.
187
seek_length = len (self.decompress.unused_data) - 8
189
# we read too much data
190
self.fileobj.seek(-seek_length, 1)
191
self._gzip_tail = self.decompress.unused_data[0:8]
192
elif seek_length < 0:
193
# we haven't read enough to check the checksum.
194
if not (-8 < seek_length):
195
raise AssertionError("too great a seek")
196
buf = self.fileobj.read(-seek_length)
197
self._gzip_tail = self.decompress.unused_data + buf
199
self._gzip_tail = self.decompress.unused_data
201
# Check the CRC and file size, and set the flag so we read
202
# a new member on the next call
204
self._new_member = True
207
"""tuned to reduce function calls and eliminate file seeking:
209
reduces lsprof count from 800 to 288
211
avoid U32 call by using struct format L
214
# We've read to the end of the file, so we should have 8 bytes of
215
# unused data in the decompressor. If we don't, there is a corrupt file.
216
# We use these 8 bytes to calculate the CRC and the recorded file size.
217
# We then check the that the computed CRC and size of the
218
# uncompressed data matches the stored values. Note that the size
219
# stored is the true file size mod 2**32.
220
if not (len(self._gzip_tail) == 8):
221
raise AssertionError("gzip trailer is incorrect length.")
222
crc32, isize = struct.unpack("<LL", self._gzip_tail)
223
# note that isize is unsigned - it can exceed 2GB
224
if crc32 != U32(self.crc):
225
raise IOError, "CRC check failed %d %d" % (crc32, U32(self.crc))
226
elif isize != LOWU32(self.size):
227
raise IOError, "Incorrect length of data produced"
229
def _read_gzip_header(self, bytes=None):
230
"""Supply bytes if the minimum header size is already read.
232
:param bytes: 10 bytes of header data.
234
"""starting cost: 300 in 3998
235
15998 reads from 3998 calls
239
bytes = self.fileobj.read(10)
241
if magic != '\037\213':
242
raise IOError, 'Not a gzipped file'
243
method = ord(bytes[2:3])
245
raise IOError, 'Unknown compression method'
246
flag = ord(bytes[3:4])
247
# modtime = self.fileobj.read(4) (bytes [4:8])
248
# extraflag = self.fileobj.read(1) (bytes[8:9])
249
# os = self.fileobj.read(1) (bytes[9:10])
250
# self.fileobj.read(6)
253
# Read & discard the extra field, if present
254
xlen = ord(self.fileobj.read(1))
255
xlen = xlen + 256*ord(self.fileobj.read(1))
256
self.fileobj.read(xlen)
258
# Read and discard a null-terminated string containing the filename
260
s = self.fileobj.read(1)
261
if not s or s=='\000':
264
# Read and discard a null-terminated string containing a comment
266
s = self.fileobj.read(1)
267
if not s or s=='\000':
270
self.fileobj.read(2) # Read & discard the 16-bit header CRC
272
def readline(self, size=-1):
273
"""Tuned to remove buffer length calls in _unread and...
275
also removes multiple len(c) calls, inlines _unread,
276
total savings - lsprof 5800 to 5300
279
8176 calls to read() in 1684
280
changing the min chunk size to 200 halved all the cache misses
281
leading to a drop to:
283
4168 call to read() in 1646
284
- i.e. just reduced the function call overhead. May be worth
287
if size < 0: size = sys.maxint
289
readsize = min(200, size) # Read from the file in small chunks
292
return "".join(bufs) # Return resulting line
295
c = self.read(readsize)
296
# number of bytes read
300
# We set i=size to break out of the loop under two
301
# conditions: 1) there's no newline, and the chunk is
302
# larger than size, or 2) there is a newline, but the
303
# resulting line would be longer than 'size'.
304
if i==-1 and len_c > size: i=size-1
305
elif size <= i: i = size -1
307
if i >= 0 or c == '':
308
# if i>= 0 we have a newline or have triggered the above
309
# if size is not None condition.
310
# if c == '' its EOF.
311
bufs.append(c[:i+1]) # Add portion of last chunk
312
# -- inlined self._unread --
313
## self._unread(c[i+1:], len_c - i) # Push back rest of chunk
314
self.extrabuf = c[i+1:] + self.extrabuf
315
self.extrasize = len_c - i + self.extrasize
316
self.offset -= len_c - i
317
# -- end inlined self._unread --
318
return ''.join(bufs) # Return resulting line
320
# Append chunk to list, decrease 'size',
323
readsize = min(size, readsize * 2)
325
def readlines(self, sizehint=0):
326
# optimise to avoid all the buffer manipulation
327
# lsprof changed from:
328
# 4168 calls in 5472 with 32000 calls to readline()
331
# Negative numbers result in reading all the lines
333
# python's gzip routine uses sizehint. This is a more efficient way
334
# than python uses to honor it. But it is even more efficient to
335
# just read the entire thing and use cStringIO to split into lines.
338
# content = self.read(sizehint)
339
# return bzrlib.osutils.split_lines(content)
340
content = StringIO(self.read(-1))
341
return content.readlines()
343
def _unread(self, buf, len_buf=None):
344
"""tuned to remove unneeded len calls.
346
because this is such an inner routine in readline, and readline is
347
in many inner loops, this has been inlined into readline().
349
The len_buf parameter combined with the reduction in len calls dropped
350
the lsprof ms count for this routine on my test data from 800 to 200 -
355
self.extrabuf = buf + self.extrabuf
356
self.extrasize = len_buf + self.extrasize
357
self.offset -= len_buf
359
def write(self, data):
360
if self.mode != gzip.WRITE:
362
raise IOError(errno.EBADF, "write() on read-only GzipFile object")
364
if self.fileobj is None:
365
raise ValueError, "write() on closed GzipFile object"
368
self.size = self.size + data_len
369
self.crc = zlib.crc32(data, self.crc)
370
self.fileobj.write( self.compress.compress(data) )
371
self.offset += data_len
373
def writelines(self, lines):
374
# profiling indicated a significant overhead
375
# calling write for each line.
376
# this batch call is a lot faster :).
377
# (4 seconds to 1 seconds for the sample upgrades I was testing).
378
self.write(''.join(lines))
added
removed
bzrlib/tuned_gzip.py
