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Revision a4dd011259fa6f3079bd0efd95b3a136c0e3c190 authored by Guido van Rossum on 15 April 2001, 22:16:26 UTC, committed by Guido van Rossum on 15 April 2001, 22:16:26 UTC
and reported to python-dev: because we were calling dict_resize() in PyDict_Next(), and because GC's dict_traverse() uses PyDict_Next(), and because PyTuple_New() can cause GC, and because dict_items() calls PyTuple_New(), it was possible for dict_items() to have the dict resized right under its nose. The solution is convoluted, and touches several places: keys(), values(), items(), popitem(), PyDict_Next(), and PyDict_SetItem(). There are two parts to it. First, we no longer call dict_resize() in PyDict_Next(), which seems to solve the immediate problem. But then PyDict_SetItem() must have a different policy about when *it* calls dict_resize(), because we want to guarantee (e.g. for an algorithm that Jeremy uses in the compiler) that you can loop over a dict using PyDict_Next() and make changes to the dict as long as those changes are only value replacements for existing keys using PyDict_SetItem(). This is done by resizing *after* the insertion instead of before, and by remembering the size before we insert the item, and if the size is still the same, we don't bother to even check if we might need to resize. An additional detail is that if the dict starts out empty, we must still resize it before the insertion. That was the first part. :-) The second part is to make keys(), values(), items(), and popitem() safe against side effects on the dict caused by allocations, under the assumption that if the GC can cause arbitrary Python code to run, it can cause other threads to run, and it's not inconceivable that our dict could be resized -- it would be insane to write code that relies on this, but not all code is sane. Now, I have this nagging feeling that the loops in lookdict probably are blissfully assuming that doing a simple key comparison does not change the dict's size. This is not necessarily true (the keys could be class instances after all). But that's a battle for another day.
1 parent 0aa30b0
Tip revision: a4dd011259fa6f3079bd0efd95b3a136c0e3c190 authored by Guido van Rossum on 15 April 2001, 22:16:26 UTC
Tentative fix for a problem that Tim discovered at the last moment,
Tentative fix for a problem that Tim discovered at the last moment,
Tip revision: a4dd011
gzip.py
"""Functions that read and write gzipped files.
The user of the file doesn't have to worry about the compression,
but random access is not allowed."""
# based on Andrew Kuchling's minigzip.py distributed with the zlib module
import struct, sys, time
import zlib
import __builtin__
__all__ = ["GzipFile","open"]
FTEXT, FHCRC, FEXTRA, FNAME, FCOMMENT = 1, 2, 4, 8, 16
READ, WRITE = 1, 2
def write32(output, value):
output.write(struct.pack("<l", value))
def write32u(output, value):
if value < 0:
value = value + 0x100000000L
output.write(struct.pack("<L", value))
def read32(input):
return struct.unpack("<l", input.read(4))[0]
def open(filename, mode="rb", compresslevel=9):
return GzipFile(filename, mode, compresslevel)
class GzipFile:
myfileobj = None
def __init__(self, filename=None, mode=None,
compresslevel=9, fileobj=None):
if fileobj is None:
fileobj = self.myfileobj = __builtin__.open(filename, mode or 'rb')
if filename is None:
if hasattr(fileobj, 'name'): filename = fileobj.name
else: filename = ''
if mode is None:
if hasattr(fileobj, 'mode'): mode = fileobj.mode
else: mode = 'rb'
if mode[0:1] == 'r':
self.mode = READ
# Set flag indicating start of a new member
self._new_member = 1
self.extrabuf = ""
self.extrasize = 0
self.filename = filename
elif mode[0:1] == 'w' or mode[0:1] == 'a':
self.mode = WRITE
self._init_write(filename)
self.compress = zlib.compressobj(compresslevel,
zlib.DEFLATED,
-zlib.MAX_WBITS,
zlib.DEF_MEM_LEVEL,
0)
else:
raise ValueError, "Mode " + mode + " not supported"
self.fileobj = fileobj
if self.mode == WRITE:
self._write_gzip_header()
def __repr__(self):
s = repr(self.fileobj)
return '<gzip ' + s[1:-1] + ' ' + hex(id(self)) + '>'
def _init_write(self, filename):
if filename[-3:] != '.gz':
filename = filename + '.gz'
self.filename = filename
self.crc = zlib.crc32("")
self.size = 0
self.writebuf = []
self.bufsize = 0
def _write_gzip_header(self):
self.fileobj.write('\037\213') # magic header
self.fileobj.write('\010') # compression method
fname = self.filename[:-3]
flags = 0
if fname:
flags = FNAME
self.fileobj.write(chr(flags))
write32u(self.fileobj, long(time.time()))
self.fileobj.write('\002')
self.fileobj.write('\377')
if fname:
self.fileobj.write(fname + '\000')
def _init_read(self):
self.crc = zlib.crc32("")
self.size = 0
def _read_gzip_header(self):
magic = self.fileobj.read(2)
if magic != '\037\213':
raise IOError, 'Not a gzipped file'
method = ord( self.fileobj.read(1) )
if method != 8:
raise IOError, 'Unknown compression method'
flag = ord( self.fileobj.read(1) )
# modtime = self.fileobj.read(4)
# extraflag = self.fileobj.read(1)
# os = self.fileobj.read(1)
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 (1):
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 (1):
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 write(self,data):
if self.fileobj is None:
raise ValueError, "write() on closed GzipFile object"
if len(data) > 0:
self.size = self.size + len(data)
self.crc = zlib.crc32(data, self.crc)
self.fileobj.write( self.compress.compress(data) )
def writelines(self,lines):
self.write(" ".join(lines))
def read(self, size=-1):
if self.extrasize <= 0 and self.fileobj is None:
return ''
readsize = 1024
if size < 0: # get the whole thing
try:
while 1:
self._read(readsize)
readsize = readsize * 2
except EOFError:
size = self.extrasize
else: # just get some more of it
try:
while size > self.extrasize:
self._read(readsize)
readsize = readsize * 2
except EOFError:
if size > self.extrasize:
size = self.extrasize
chunk = self.extrabuf[:size]
self.extrabuf = self.extrabuf[size:]
self.extrasize = self.extrasize - size
return chunk
def _unread(self, buf):
self.extrabuf = buf + self.extrabuf
self.extrasize = len(buf) + self.extrasize
def _read(self, size=1024):
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.
pos = self.fileobj.tell() # Save current position
self.fileobj.seek(0, 2) # Seek to end of file
if pos == self.fileobj.tell():
self.fileobj = None
raise EOFError, "Reached EOF"
else:
self.fileobj.seek( pos ) # Return to original position
self._init_read()
self._read_gzip_header()
self.decompress = zlib.decompressobj(-zlib.MAX_WBITS)
self._new_member = 0
# 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 == "":
uncompress = self.decompress.flush()
self._read_eof()
self.fileobj = None
self._add_read_data( uncompress )
raise EOFError, 'Reached EOF'
uncompress = self.decompress.decompress(buf)
self._add_read_data( uncompress )
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 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 _read_eof() will rewind a further 8 bytes)
self.fileobj.seek( -len(self.decompress.unused_data)+8, 1)
# 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 = 1
def _add_read_data(self, data):
self.crc = zlib.crc32(data, self.crc)
self.extrabuf = self.extrabuf + data
self.extrasize = self.extrasize + len(data)
self.size = self.size + len(data)
def _read_eof(self):
# We've read to the end of the file, so we have to rewind in order
# to reread the 8 bytes containing the CRC and the file size.
# We check the that the computed CRC and size of the
# uncompressed data matches the stored values.
self.fileobj.seek(-8, 1)
crc32 = read32(self.fileobj)
isize = read32(self.fileobj)
if crc32%0x100000000L != self.crc%0x100000000L:
raise ValueError, "CRC check failed"
elif isize != self.size:
raise ValueError, "Incorrect length of data produced"
def close(self):
if self.mode == WRITE:
self.fileobj.write(self.compress.flush())
write32(self.fileobj, self.crc)
write32(self.fileobj, self.size)
self.fileobj = None
elif self.mode == READ:
self.fileobj = None
if self.myfileobj:
self.myfileobj.close()
self.myfileobj = None
def __del__(self):
try:
if (self.myfileobj is None and
self.fileobj is None):
return
except AttributeError:
return
self.close()
def flush(self):
self.fileobj.flush()
def isatty(self):
return 0
def readline(self, size=-1):
if size < 0: size = sys.maxint
bufs = []
orig_size = size
readsize = min(100, size) # Read from the file in small chunks
while 1:
if size == 0:
return "".join(bufs) # Return resulting line
c = self.read(readsize)
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 == '':
bufs.append(c[:i+1]) # Add portion of last chunk
self._unread(c[i+1:]) # Push back rest of chunk
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):
# Negative numbers result in reading all the lines
if sizehint <= 0: sizehint = sys.maxint
L = []
while sizehint > 0:
line = self.readline()
if line == "": break
L.append( line )
sizehint = sizehint - len(line)
return L
def writelines(self, L):
for line in L:
self.write(line)
def _test():
# Act like gzip; with -d, act like gunzip.
# The input file is not deleted, however, nor are any other gzip
# options or features supported.
import sys
args = sys.argv[1:]
decompress = args and args[0] == "-d"
if decompress:
args = args[1:]
if not args:
args = ["-"]
for arg in args:
if decompress:
if arg == "-":
f = GzipFile(filename="", mode="rb", fileobj=sys.stdin)
g = sys.stdout
else:
if arg[-3:] != ".gz":
print "filename doesn't end in .gz:", `arg`
continue
f = open(arg, "rb")
g = __builtin__.open(arg[:-3], "wb")
else:
if arg == "-":
f = sys.stdin
g = GzipFile(filename="", mode="wb", fileobj=sys.stdout)
else:
f = __builtin__.open(arg, "rb")
g = open(arg + ".gz", "wb")
while 1:
chunk = f.read(1024)
if not chunk:
break
g.write(chunk)
if g is not sys.stdout:
g.close()
if f is not sys.stdin:
f.close()
if __name__ == '__main__':
_test()
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