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Merged revisions 88528 via svnmerge from

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........
  r88528 | lars.gustaebel | 2011-02-23 12:42:22 +0100 (Wed, 23 Feb 2011) | 16 lines

  Issue #11224: Improved sparse file read support (r85916) introduced a
  regression in _FileInFile which is used in file-like objects returned
  by TarFile.extractfile(). The inefficient design of the
  _FileInFile.read() method causes various dramatic side-effects and
  errors:

    - The data segment of a file member is read completely into memory
      every(!) time a small block is accessed. This is not only slow
      but may cause unexpected MemoryErrors with very large files.
    - Reading members from compressed tar archives is even slower
      because of the excessive backwards seeking which is done when the
      same data segment is read over and over again.
    - As a backwards seek on a TarFile opened in stream mode is not
      possible, using extractfile() fails with a StreamError.
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This commit is contained in:
Lars Gustäbel 2011-02-23 11:52:31 +00:00
parent dcb29c93d2
commit 9f6cbe09cc
3 changed files with 22 additions and 3 deletions
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5
Lib/tarfile.py
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@ -760,9 +760,8 @@ class _FileInFile(object):
self.map_index = 0
length = min(size, stop - self.position)
if data:
self.fileobj.seek(offset)
block = self.fileobj.read(stop - start)
buf += block[self.position - start:self.position + length]
self.fileobj.seek(offset + (self.position - start))
buf += self.fileobj.read(length)
else:
buf += NUL * length
size -= length