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# Copyright (C) 2005, 2006 Canonical Ltd
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 2 of the License, or
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# (at your option) any later version.
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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# You should have received a copy of the GNU General Public License
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# along with this program; if not, write to the Free Software
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# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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return (scheme, username, password, host, port, path)
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class _CoalescedOffset(object):
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"""A data container for keeping track of coalesced offsets."""
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__slots__ = ['start', 'length', 'ranges']
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def __init__(self, start, length, ranges):
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def __cmp__(self, other):
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return cmp((self.start, self.length, self.ranges),
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(other.start, other.length, other.ranges))
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class Transport(object):
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"""This class encapsulates methods for retrieving or putting a file
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from/to a storage location.
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:offsets: A list of (offset, size) tuples.
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:return: A list or generator of (offset, data) tuples
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def do_combined_read(combined_offsets):
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for offset, size in combined_offsets:
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mutter('readv coalesced %d reads.', len(combined_offsets))
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offset = combined_offsets[0][0]
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data = fp.read(total_size)
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for offset, size in combined_offsets:
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yield offset, data[pos:pos + size]
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fp = self.get(relpath)
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pending_offsets = deque(offsets)
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combined_offsets = []
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while len(pending_offsets):
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offset, size = pending_offsets.popleft()
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if not combined_offsets:
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combined_offsets = [[offset, size]]
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return self._seek_and_read(fp, offsets)
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def _seek_and_read(self, fp, offsets):
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"""An implementation of readv that uses fp.seek and fp.read.
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This uses _coalesce_offsets to issue larger reads and fewer seeks.
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:param fp: A file-like object that supports seek() and read(size)
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:param offsets: A list of offsets to be read from the given file.
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:return: yield (pos, data) tuples for each request
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# We are going to iterate multiple times, we need a list
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offsets = list(offsets)
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sorted_offsets = sorted(offsets)
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# turn the list of offsets into a stack
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offset_stack = iter(offsets)
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cur_offset_and_size = offset_stack.next()
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coalesced = self._coalesce_offsets(sorted_offsets,
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limit=self._max_readv_combine,
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fudge_factor=self._bytes_to_read_before_seek)
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# Cache the results, but only until they have been fulfilled
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for c_offset in coalesced:
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# TODO: jam 20060724 it might be faster to not issue seek if
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# we are already at the right location. This should be
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fp.seek(c_offset.start)
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data = fp.read(c_offset.length)
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for suboffset, subsize in c_offset.ranges:
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key = (c_offset.start+suboffset, subsize)
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data_map[key] = data[suboffset:suboffset+subsize]
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# Now that we've read some data, see if we can yield anything back
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while cur_offset_and_size in data_map:
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this_data = data_map.pop(cur_offset_and_size)
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yield cur_offset_and_size[0], this_data
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cur_offset_and_size = offset_stack.next()
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def _coalesce_offsets(offsets, limit, fudge_factor):
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"""Yield coalesced offsets.
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With a long list of neighboring requests, combine them
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into a single large request, while retaining the original
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Turns [(15, 10), (25, 10)] => [(15, 20, [(0, 10), (10, 10)])]
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:param offsets: A list of (start, length) pairs
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:param limit: Only combine a maximum of this many pairs
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Some transports penalize multiple reads more than
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others, and sometimes it is better to return early.
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:param fudge_factor: All transports have some level of 'it is
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better to read some more data and throw it away rather
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than seek', so collapse if we are 'close enough'
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:return: yield _CoalescedOffset objects, which have members for wher
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to start, how much to read, and how to split those
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cur = _CoalescedOffset(None, None, [])
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for start, size in offsets:
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if (last_end is not None
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and start <= last_end + fudge_factor
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and start >= cur.start
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and (limit <= 0 or len(cur.ranges) < limit)):
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cur.length = end - cur.start
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cur.ranges.append((start-cur.start, size))
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if (len(combined_offsets) < 50 and
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combined_offsets[-1][0] + combined_offsets[-1][1] == offset):
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combined_offsets.append([offset, size])
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# incompatible, or over the threshold issue a read and yield
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pending_offsets.appendleft((offset, size))
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for result in do_combined_read(combined_offsets):
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combined_offsets = []
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# whatever is left is a single coalesced request
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if len(combined_offsets):
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for result in do_combined_read(combined_offsets):
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if cur.start is not None:
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cur = _CoalescedOffset(start, size, [(0, size)])
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if cur.start is not None:
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def get_multi(self, relpaths, pb=None):
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"""Get a list of file-like objects, one for each entry in relpaths.
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bzrlib/transport/__init__.py
