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Merged
methane merged 3 commits into from
Jul 6, 2018
Merged

bpo-34043: Optimize tarfile uncompress performance #8089

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35c4e9c
bpo-34043: Optimize tarfile uncompress performance
methane Jul 4, 2018
ab33cea
split two assignments
methane Jul 5, 2018
cd48a2c
fix typo
methane Jul 5, 2018
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30 changes: 12 additions & 18 deletions Lib/tarfile.py
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Original file line number Diff line number Diff line change
Expand Up @@ -513,21 +513,10 @@ def seek(self, pos=0):
raise StreamError("seeking backwards is not allowed")
return self.pos

def read(self, size=None):
"""Return the next size number of bytes from the stream.
If size is not defined, return all bytes of the stream
up to EOF.
"""
if size is None:

@serhiy-storchaka serhiy-storchaka Jul 6, 2018

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I have only one question. Why this branch was removed?

@methane methane Jul 6, 2018

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This issue is follow up of bpo-34010, (GH-8020).
See also, https://bugs.python.org/issue34010#msg321040

@serhiy-storchaka serhiy-storchaka Jul 6, 2018

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Thank you. Instances of _Stream are never leaked to the end user? Then this change LGTM.

@methane methane Jul 6, 2018 •
edited
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It can be accessed via TarFile.fileobj.
But using it directly is not pragramatic, and TarFile.fileobj.read() caused TypeError because of "".join() bug.
So it must not used for previous versions.

@vstinner vstinner Jul 6, 2018

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I saw that the class is private, but I didn't notice that TarFile.fileobj is public. Maybe just replace the assertion with a regular if/raise, just in case? Maybe raise a NotImplementedError?

t = []
while True:
buf = self._read(self.bufsize)
if not buf:
break
t.append(buf)
buf = b"".join(t)
else:
buf = self._read(size)
def read(self, size):
"""Return the next size number of bytes from the stream."""
assert size is not None
buf = self._read(size)
self.pos += len(buf)
return buf

Expand All @@ -540,9 +529,14 @@ def _read(self, size):
c = len(self.dbuf)
t = [self.dbuf]
while c < size:
buf = self.__read(self.bufsize)
if not buf:
break
# Skip underlying buffer to avoid unaligned double buffering.
if self.buf:
buf = self.buf
self.buf = b""
else:
buf = self.fileobj.read(self.bufsize)
if not buf:
break
try:
buf = self.cmp.decompress(buf)
except self.exception:
Expand Down
1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Library/2018-07-04-21-14-35.bpo-34043.0YJNq9.rst
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@@ -0,0 +1 @@
Optimize tarfile uncompress performance about 15% when gzip is used.