ExternalVendorCode/tahoe-lafs
1
0
Fork 0
mirror of https://github.com/tahoe-lafs/tahoe-lafs.git synced 2024-12-30 01:38:55 +00:00
Code Issues Actions Packages Projects Releases Wiki Activity

Add a byte-spans utility class, like perl's Set::IntSpan for .newsrc files.

Browse Source 
Also a data-spans class, which records a byte (instead of a bit) for each
index.
This commit is contained in:
Brian Warner 2010-08-04 00:26:00 -07:00
parent cd360c847c
commit cbcb728e7e
2 changed files with 996 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

565
src/allmydata/test/test_util.py
View File

@ -7,12 +7,14 @@ from twisted.trial import unittest
from twisted.internet import defer, reactor
from twisted.python.failure import Failure
from twisted.python import log
from hashlib import md5
from allmydata.util import base32, idlib, humanreadable, mathutil, hashutil
from allmydata.util import assertutil, fileutil, deferredutil, abbreviate
from allmydata.util import limiter, time_format, pollmixin, cachedir
from allmydata.util import statistics, dictutil, pipeline
from allmydata.util import log as tahoe_log
from allmydata.util.spans import Spans, overlap, DataSpans
class Base32(unittest.TestCase):
def test_b2a_matches_Pythons(self):
@ -1568,3 +1570,566 @@ class Log(unittest.TestCase):
tahoe_log.err(format="intentional sample error",
failure=f, level=tahoe_log.OPERATIONAL, umid="wO9UoQ")
self.flushLoggedErrors(SampleError)
class SimpleSpans:
# this is a simple+inefficient form of util.spans.Spans . We compare the
# behavior of this reference model against the real (efficient) form.
def __init__(self, _span_or_start=None, length=None):
self._have = set()
if length is not None:
for i in range(_span_or_start, _span_or_start+length):
self._have.add(i)
elif _span_or_start:
for (start,length) in _span_or_start:
self.add(start, length)
def add(self, start, length):
for i in range(start, start+length):
self._have.add(i)
return self
def remove(self, start, length):
for i in range(start, start+length):
self._have.discard(i)
return self
def each(self):
return sorted(self._have)
def __iter__(self):
items = sorted(self._have)
prevstart = None
prevend = None
for i in items:
if prevstart is None:
prevstart = prevend = i
continue
if i == prevend+1:
prevend = i
continue
yield (prevstart, prevend-prevstart+1)
prevstart = prevend = i
if prevstart is not None:
yield (prevstart, prevend-prevstart+1)
def __len__(self):
# this also gets us bool(s)
return len(self._have)
def __add__(self, other):
s = self.__class__(self)
for (start, length) in other:
s.add(start, length)
return s
def __sub__(self, other):
s = self.__class__(self)
for (start, length) in other:
s.remove(start, length)
return s
def __iadd__(self, other):
for (start, length) in other:
self.add(start, length)
return self
def __isub__(self, other):
for (start, length) in other:
self.remove(start, length)
return self
def __and__(self, other):
s = self.__class__()
for i in other.each():
if i in self._have:
s.add(i, 1)
return s
def __contains__(self, (start,length)):
for i in range(start, start+length):
if i not in self._have:
return False
return True
class ByteSpans(unittest.TestCase):
def test_basic(self):
s = Spans()
self.failUnlessEqual(list(s), [])
self.failIf(s)
self.failIf((0,1) in s)
self.failUnlessEqual(len(s), 0)
s1 = Spans(3, 4) # 3,4,5,6
self._check1(s1)
s2 = Spans(s1)
self._check1(s2)
s2.add(10,2) # 10,11
self._check1(s1)
self.failUnless((10,1) in s2)
self.failIf((10,1) in s1)
self.failUnlessEqual(list(s2.each()), [3,4,5,6,10,11])
self.failUnlessEqual(len(s2), 6)
s2.add(15,2).add(20,2)
self.failUnlessEqual(list(s2.each()), [3,4,5,6,10,11,15,16,20,21])
self.failUnlessEqual(len(s2), 10)
s2.remove(4,3).remove(15,1)
self.failUnlessEqual(list(s2.each()), [3,10,11,16,20,21])
self.failUnlessEqual(len(s2), 6)
s1 = SimpleSpans(3, 4) # 3 4 5 6
s2 = SimpleSpans(5, 4) # 5 6 7 8
i = s1 & s2
self.failUnlessEqual(list(i.each()), [5, 6])
def _check1(self, s):
self.failUnlessEqual(list(s), [(3,4)])
self.failUnless(s)
self.failUnlessEqual(len(s), 4)
self.failIf((0,1) in s)
self.failUnless((3,4) in s)
self.failUnless((3,1) in s)
self.failUnless((5,2) in s)
self.failUnless((6,1) in s)
self.failIf((6,2) in s)
self.failIf((7,1) in s)
self.failUnlessEqual(list(s.each()), [3,4,5,6])
def test_math(self):
s1 = Spans(0, 10) # 0,1,2,3,4,5,6,7,8,9
s2 = Spans(5, 3) # 5,6,7
s3 = Spans(8, 4) # 8,9,10,11
s = s1 - s2
self.failUnlessEqual(list(s.each()), [0,1,2,3,4,8,9])
s = s1 - s3
self.failUnlessEqual(list(s.each()), [0,1,2,3,4,5,6,7])
s = s2 - s3
self.failUnlessEqual(list(s.each()), [5,6,7])
s = s1 & s2
self.failUnlessEqual(list(s.each()), [5,6,7])
s = s2 & s1
self.failUnlessEqual(list(s.each()), [5,6,7])
s = s1 & s3
self.failUnlessEqual(list(s.each()), [8,9])
s = s3 & s1
self.failUnlessEqual(list(s.each()), [8,9])
s = s2 & s3
self.failUnlessEqual(list(s.each()), [])
s = s3 & s2
self.failUnlessEqual(list(s.each()), [])
s = Spans() & s3
self.failUnlessEqual(list(s.each()), [])
s = s3 & Spans()
self.failUnlessEqual(list(s.each()), [])
s = s1 + s2
self.failUnlessEqual(list(s.each()), [0,1,2,3,4,5,6,7,8,9])
s = s1 + s3
self.failUnlessEqual(list(s.each()), [0,1,2,3,4,5,6,7,8,9,10,11])
s = s2 + s3
self.failUnlessEqual(list(s.each()), [5,6,7,8,9,10,11])
s = Spans(s1)
s -= s2
self.failUnlessEqual(list(s.each()), [0,1,2,3,4,8,9])
s = Spans(s1)
s -= s3
self.failUnlessEqual(list(s.each()), [0,1,2,3,4,5,6,7])
s = Spans(s2)
s -= s3
self.failUnlessEqual(list(s.each()), [5,6,7])
s = Spans(s1)
s += s2
self.failUnlessEqual(list(s.each()), [0,1,2,3,4,5,6,7,8,9])
s = Spans(s1)
s += s3
self.failUnlessEqual(list(s.each()), [0,1,2,3,4,5,6,7,8,9,10,11])
s = Spans(s2)
s += s3
self.failUnlessEqual(list(s.each()), [5,6,7,8,9,10,11])
def test_random(self):
# attempt to increase coverage of corner cases by comparing behavior
# of a simple-but-slow model implementation against the
# complex-but-fast actual implementation, in a large number of random
# operations
S1 = SimpleSpans
S2 = Spans
s1 = S1(); s2 = S2()
seed = ""
def _create(subseed):
ns1 = S1(); ns2 = S2()
for i in range(10):
what = md5(subseed+str(i)).hexdigest()
start = int(what[2:4], 16)
length = max(1,int(what[5:6], 16))
ns1.add(start, length); ns2.add(start, length)
return ns1, ns2
#print
for i in range(1000):
what = md5(seed+str(i)).hexdigest()
op = what[0]
subop = what[1]
start = int(what[2:4], 16)
length = max(1,int(what[5:6], 16))
#print what
if op in "0":
if subop in "01234":
s1 = S1(); s2 = S2()
elif subop in "5678":
s1 = S1(start, length); s2 = S2(start, length)
else:
s1 = S1(s1); s2 = S2(s2)
#print "s2 = %s" % s2.dump()
elif op in "123":
#print "s2.add(%d,%d)" % (start, length)
s1.add(start, length); s2.add(start, length)
elif op in "456":
#print "s2.remove(%d,%d)" % (start, length)
s1.remove(start, length); s2.remove(start, length)
elif op in "78":
ns1, ns2 = _create(what[7:11])
#print "s2 + %s" % ns2.dump()
s1 = s1 + ns1; s2 = s2 + ns2
elif op in "9a":
ns1, ns2 = _create(what[7:11])
#print "%s - %s" % (s2.dump(), ns2.dump())
s1 = s1 - ns1; s2 = s2 - ns2
elif op in "bc":
ns1, ns2 = _create(what[7:11])
#print "s2 += %s" % ns2.dump()
s1 += ns1; s2 += ns2
elif op in "de":
ns1, ns2 = _create(what[7:11])
#print "%s -= %s" % (s2.dump(), ns2.dump())
s1 -= ns1; s2 -= ns2
else:
ns1, ns2 = _create(what[7:11])
#print "%s &= %s" % (s2.dump(), ns2.dump())
s1 = s1 & ns1; s2 = s2 & ns2
#print "s2 now %s" % s2.dump()
self.failUnlessEqual(list(s1.each()), list(s2.each()))
self.failUnlessEqual(len(s1), len(s2))
self.failUnlessEqual(bool(s1), bool(s2))
self.failUnlessEqual(list(s1), list(s2))
for j in range(10):
what = md5(what[12:14]+str(j)).hexdigest()
start = int(what[2:4], 16)
length = max(1, int(what[5:6], 16))
span = (start, length)
self.failUnlessEqual(bool(span in s1), bool(span in s2))
# s()
# s(start,length)
# s(s0)
# s.add(start,length) : returns s
# s.remove(start,length)
# s.each() -> list of byte offsets, mostly for testing
# list(s) -> list of (start,length) tuples, one per span
# (start,length) in s -> True if (start..start+length-1) are all members
# NOT equivalent to x in list(s)
# len(s) -> number of bytes, for testing, bool(), and accounting/limiting
# bool(s) (__len__)
# s = s1+s2, s1-s2, +=s1, -=s1
def test_overlap(self):
for a in range(20):
for b in range(10):
for c in range(20):
for d in range(10):
self._test_overlap(a,b,c,d)
def _test_overlap(self, a, b, c, d):
s1 = set(range(a,a+b))
s2 = set(range(c,c+d))
#print "---"
#self._show_overlap(s1, "1")
#self._show_overlap(s2, "2")
o = overlap(a,b,c,d)
expected = s1.intersection(s2)
if not expected:
self.failUnlessEqual(o, None)
else:
start,length = o
so = set(range(start,start+length))
#self._show(so, "o")
self.failUnlessEqual(so, expected)
def _show_overlap(self, s, c):
import sys
out = sys.stdout
if s:
for i in range(max(s)):
if i in s:
out.write(c)
else:
out.write(" ")
out.write("\n")
def extend(s, start, length, fill):
if len(s) >= start+length:
return s
assert len(fill) == 1
return s + fill*(start+length-len(s))
def replace(s, start, data):
assert len(s) >= start+len(data)
return s[:start] + data + s[start+len(data):]
class SimpleDataSpans:
def __init__(self, other=None):
self.missing = "" # "1" where missing, "0" where found
self.data = ""
if other:
for (start, data) in other.get_chunks():
self.add(start, data)
def __len__(self):
return len(self.missing.translate(None, "1"))
def _dump(self):
return [i for (i,c) in enumerate(self.missing) if c == "0"]
def _have(self, start, length):
m = self.missing[start:start+length]
if not m or len(m)<length or int(m):
return False
return True
def get_chunks(self):
for i in self._dump():
yield (i, self.data[i])
def get_spans(self):
return SimpleSpans([(start,len(data))
for (start,data) in self.get_chunks()])
def get(self, start, length):
if self._have(start, length):
return self.data[start:start+length]
return None
def pop(self, start, length):
data = self.get(start, length)
if data:
self.remove(start, length)
return data
def remove(self, start, length):
self.missing = replace(extend(self.missing, start, length, "1"),
start, "1"*length)
def add(self, start, data):
self.missing = replace(extend(self.missing, start, len(data), "1"),
start, "0"*len(data))
self.data = replace(extend(self.data, start, len(data), " "),
start, data)
class StringSpans(unittest.TestCase):
def do_basic(self, klass):
ds = klass()
self.failUnlessEqual(len(ds), 0)
self.failUnlessEqual(list(ds._dump()), [])
self.failUnlessEqual(sum([len(d) for (s,d) in ds.get_chunks()]), 0)
s = ds.get_spans()
self.failUnlessEqual(ds.get(0, 4), None)
self.failUnlessEqual(ds.pop(0, 4), None)
ds.remove(0, 4)
ds.add(2, "four")
self.failUnlessEqual(len(ds), 4)
self.failUnlessEqual(list(ds._dump()), [2,3,4,5])
self.failUnlessEqual(sum([len(d) for (s,d) in ds.get_chunks()]), 4)
s = ds.get_spans()
self.failUnless((2,2) in s)
self.failUnlessEqual(ds.get(0, 4), None)
self.failUnlessEqual(ds.pop(0, 4), None)
self.failUnlessEqual(ds.get(4, 4), None)
ds2 = klass(ds)
self.failUnlessEqual(len(ds2), 4)
self.failUnlessEqual(list(ds2._dump()), [2,3,4,5])
self.failUnlessEqual(sum([len(d) for (s,d) in ds2.get_chunks()]), 4)
self.failUnlessEqual(ds2.get(0, 4), None)
self.failUnlessEqual(ds2.pop(0, 4), None)
self.failUnlessEqual(ds2.pop(2, 3), "fou")
self.failUnlessEqual(sum([len(d) for (s,d) in ds2.get_chunks()]), 1)
self.failUnlessEqual(ds2.get(2, 3), None)
self.failUnlessEqual(ds2.get(5, 1), "r")
self.failUnlessEqual(ds.get(2, 3), "fou")
self.failUnlessEqual(sum([len(d) for (s,d) in ds.get_chunks()]), 4)
ds.add(0, "23")
self.failUnlessEqual(len(ds), 6)
self.failUnlessEqual(list(ds._dump()), [0,1,2,3,4,5])
self.failUnlessEqual(sum([len(d) for (s,d) in ds.get_chunks()]), 6)
self.failUnlessEqual(ds.get(0, 4), "23fo")
self.failUnlessEqual(ds.pop(0, 4), "23fo")
self.failUnlessEqual(sum([len(d) for (s,d) in ds.get_chunks()]), 2)
self.failUnlessEqual(ds.get(0, 4), None)
self.failUnlessEqual(ds.pop(0, 4), None)
ds = klass()
ds.add(2, "four")
ds.add(3, "ea")
self.failUnlessEqual(ds.get(2, 4), "fear")
def do_scan(self, klass):
# do a test with gaps and spans of size 1 and 2
# left=(1,11) * right=(1,11) * gapsize=(1,2)
# 111, 112, 121, 122, 211, 212, 221, 222
# 211
# 121
# 112
# 212
# 222
# 221
# 111
# 122
# 11 1 1 11 11 11 1 1 111
# 0123456789012345678901234567
# abcdefghijklmnopqrstuvwxyz-=
pieces = [(1, "bc"),
(4, "e"),
(7, "h"),
(9, "jk"),
(12, "mn"),
(16, "qr"),
(20, "u"),
(22, "w"),
(25, "z-="),
]
p_elements = set([1,2,4,7,9,10,12,13,16,17,20,22,25,26,27])
S = "abcdefghijklmnopqrstuvwxyz-="
# TODO: when adding data, add capital letters, to make sure we aren't
# just leaving the old data in place
l = len(S)
def base():
ds = klass()
for start, data in pieces:
ds.add(start, data)
return ds
def dump(s):
p = set(s._dump())
# wow, this is the first time I've ever wanted ?: in python
# note: this requires python2.5
d = "".join([(S[i] if i in p else " ") for i in range(l)])
assert len(d) == l
return d
DEBUG = False
for start in range(0, l):
for end in range(start+1, l):
# add [start-end) to the baseline
which = "%d-%d" % (start, end-1)
p_added = set(range(start, end))
b = base()
if DEBUG:
print
print dump(b), which
add = klass(); add.add(start, S[start:end])
print dump(add)
b.add(start, S[start:end])
if DEBUG:
print dump(b)
# check that the new span is there
d = b.get(start, end-start)
self.failUnlessEqual(d, S[start:end], which)
# check that all the original pieces are still there
for t_start, t_data in pieces:
t_len = len(t_data)
self.failUnlessEqual(b.get(t_start, t_len),
S[t_start:t_start+t_len],
"%s %d+%d" % (which, t_start, t_len))
# check that a lot of subspans are mostly correct
for t_start in range(l):
for t_len in range(1,4):
d = b.get(t_start, t_len)
if d is not None:
which2 = "%s+(%d-%d)" % (which, t_start,
t_start+t_len-1)
self.failUnlessEqual(d, S[t_start:t_start+t_len],
which2)
# check that removing a subspan gives the right value
b2 = klass(b)
b2.remove(t_start, t_len)
removed = set(range(t_start, t_start+t_len))
for i in range(l):
exp = (((i in p_elements) or (i in p_added))
and (i not in removed))
which2 = "%s-(%d-%d)" % (which, t_start,
t_start+t_len-1)
self.failUnlessEqual(bool(b2.get(i, 1)), exp,
which2+" %d" % i)
def test_test(self):
self.do_basic(SimpleDataSpans)
self.do_scan(SimpleDataSpans)
def test_basic(self):
self.do_basic(DataSpans)
self.do_scan(DataSpans)
def test_random(self):
# attempt to increase coverage of corner cases by comparing behavior
# of a simple-but-slow model implementation against the
# complex-but-fast actual implementation, in a large number of random
# operations
S1 = SimpleDataSpans
S2 = DataSpans
s1 = S1(); s2 = S2()
seed = ""
def _randstr(length, seed):
created = 0
pieces = []
while created < length:
piece = md5(seed + str(created)).hexdigest()
pieces.append(piece)
created += len(piece)
return "".join(pieces)[:length]
def _create(subseed):
ns1 = S1(); ns2 = S2()
for i in range(10):
what = md5(subseed+str(i)).hexdigest()
start = int(what[2:4], 16)
length = max(1,int(what[5:6], 16))
ns1.add(start, _randstr(length, what[7:9]));
ns2.add(start, _randstr(length, what[7:9]))
return ns1, ns2
#print
for i in range(1000):
what = md5(seed+str(i)).hexdigest()
op = what[0]
subop = what[1]
start = int(what[2:4], 16)
length = max(1,int(what[5:6], 16))
#print what
if op in "0":
if subop in "0123456":
s1 = S1(); s2 = S2()
else:
s1, s2 = _create(what[7:11])
#print "s2 = %s" % list(s2._dump())
elif op in "123456":
#print "s2.add(%d,%d)" % (start, length)
s1.add(start, _randstr(length, what[7:9]));
s2.add(start, _randstr(length, what[7:9]))
elif op in "789abc":
#print "s2.remove(%d,%d)" % (start, length)
s1.remove(start, length); s2.remove(start, length)
else:
#print "s2.pop(%d,%d)" % (start, length)
d1 = s1.pop(start, length); d2 = s2.pop(start, length)
self.failUnlessEqual(d1, d2)
#print "s1 now %s" % list(s1._dump())
#print "s2 now %s" % list(s2._dump())
self.failUnlessEqual(len(s1), len(s2))
self.failUnlessEqual(list(s1._dump()), list(s2._dump()))
for j in range(100):
what = md5(what[12:14]+str(j)).hexdigest()
start = int(what[2:4], 16)
length = max(1, int(what[5:6], 16))
d1 = s1.get(start, length); d2 = s2.get(start, length)
self.failUnlessEqual(d1, d2, "%d+%d" % (start, length))

431
src/allmydata/util/spans.py Executable file
View File

@ -0,0 +1,431 @@
class Spans:
"""I represent a compressed list of booleans, one per index (an integer).
Typically, each index represents an offset into a large string, pointing
to a specific byte of a share. In this context, True means that byte has
been received, or has been requested.
Another way to look at this is maintaining a set of integers, optimized
for operations on spans like 'add range to set' and 'is range in set?'.
This is a python equivalent of perl's Set::IntSpan module, frequently
used to represent .newsrc contents.
Rather than storing an actual (large) list or dictionary, I represent my
internal state as a sorted list of spans, each with a start and a length.
My API is presented in terms of start+length pairs. I provide set
arithmetic operators, to efficiently answer questions like 'I want bytes
XYZ, I already requested bytes ABC, and I've already received bytes DEF:
what bytes should I request now?'.
The new downloader will use it to keep track of which bytes we've requested
or received already.
"""
def __init__(self, _span_or_start=None, length=None):
self._spans = list()
if length is not None:
self._spans.append( (_span_or_start, length) )
elif _span_or_start:
for (start,length) in _span_or_start:
self.add(start, length)
self._check()
def _check(self):
assert sorted(self._spans) == self._spans
prev_end = None
try:
for (start,length) in self._spans:
if prev_end is not None:
assert start > prev_end
prev_end = start+length
except AssertionError:
print "BAD:", self.dump()
raise
def add(self, start, length):
assert start >= 0
assert length > 0
#print " ADD [%d+%d -%d) to %s" % (start, length, start+length, self.dump())
first_overlap = last_overlap = None
for i,(s_start,s_length) in enumerate(self._spans):
#print " (%d+%d)-> overlap=%s adjacent=%s" % (s_start,s_length, overlap(s_start, s_length, start, length), adjacent(s_start, s_length, start, length))
if (overlap(s_start, s_length, start, length)
or adjacent(s_start, s_length, start, length)):
last_overlap = i
if first_overlap is None:
first_overlap = i
continue
# no overlap
if first_overlap is not None:
break
#print " first_overlap", first_overlap, last_overlap
if first_overlap is None:
# no overlap, so just insert the span and sort by starting
# position.
self._spans.insert(0, (start,length))
self._spans.sort()
else:
# everything from [first_overlap] to [last_overlap] overlapped
first_start,first_length = self._spans[first_overlap]
last_start,last_length = self._spans[last_overlap]
newspan_start = min(start, first_start)
newspan_end = max(start+length, last_start+last_length)
newspan_length = newspan_end - newspan_start
newspan = (newspan_start, newspan_length)
self._spans[first_overlap:last_overlap+1] = [newspan]
#print " ADD done: %s" % self.dump()
self._check()
return self
def remove(self, start, length):
assert start >= 0
assert length > 0
#print " REMOVE [%d+%d -%d) from %s" % (start, length, start+length, self.dump())
first_complete_overlap = last_complete_overlap = None
for i,(s_start,s_length) in enumerate(self._spans):
s_end = s_start + s_length
o = overlap(s_start, s_length, start, length)
if o:
o_start, o_length = o
o_end = o_start+o_length
if o_start == s_start and o_end == s_end:
# delete this span altogether
if first_complete_overlap is None:
first_complete_overlap = i
last_complete_overlap = i
elif o_start == s_start:
# we only overlap the left side, so trim the start
# 1111
# rrrr
# oo
# -> 11
new_start = o_end
new_end = s_end
assert new_start > s_start
new_length = new_end - new_start
self._spans[i] = (new_start, new_length)
elif o_end == s_end:
# we only overlap the right side
# 1111
# rrrr
# oo
# -> 11
new_start = s_start
new_end = o_start
assert new_end < s_end
new_length = new_end - new_start
self._spans[i] = (new_start, new_length)
else:
# we overlap the middle, so create a new span. No need to
# examine any other spans.
# 111111
# rr
# LL RR
left_start = s_start
left_end = o_start
left_length = left_end - left_start
right_start = o_end
right_end = s_end
right_length = right_end - right_start
self._spans[i] = (left_start, left_length)
self._spans.append( (right_start, right_length) )
self._spans.sort()
break
if first_complete_overlap is not None:
del self._spans[first_complete_overlap:last_complete_overlap+1]
#print " REMOVE done: %s" % self.dump()
self._check()
return self
def dump(self):
return "len=%d: %s" % (len(self),
",".join(["[%d-%d]" % (start,start+l-1)
for (start,l) in self._spans]) )
def each(self):
for start, length in self._spans:
for i in range(start, start+length):
yield i
def __iter__(self):
for s in self._spans:
yield s
def __len__(self):
# this also gets us bool(s)
return sum([length for start,length in self._spans])
def __add__(self, other):
s = self.__class__(self)
for (start, length) in other:
s.add(start, length)
return s
def __sub__(self, other):
s = self.__class__(self)
for (start, length) in other:
s.remove(start, length)
return s
def __iadd__(self, other):
for (start, length) in other:
self.add(start, length)
return self
def __isub__(self, other):
for (start, length) in other:
self.remove(start, length)
return self
def __and__(self, other):
if not self._spans:
return self.__class__()
bounds = self.__class__(self._spans[0][0],
self._spans[-1][0]+self._spans[-1][1])
not_other = bounds - other
return self - not_other
def __contains__(self, (start,length)):
for span_start,span_length in self._spans:
o = overlap(start, length, span_start, span_length)
if o:
o_start,o_length = o
if o_start == start and o_length == length:
return True
return False
def overlap(start0, length0, start1, length1):
# return start2,length2 of the overlapping region, or None
# 00 00 000 0000 00 00 000 00 00 00 00
# 11 11 11 11 111 11 11 1111 111 11 11
left = max(start0, start1)
right = min(start0+length0, start1+length1)
# if there is overlap, 'left' will be its start, and right-1 will
# be the end'
if left < right:
return (left, right-left)
return None
def adjacent(start0, length0, start1, length1):
if (start0 < start1) and start0+length0 == start1:
return True
elif (start1 < start0) and start1+length1 == start0:
return True
return False
class DataSpans:
"""I represent portions of a large string. Equivalently, I can be said to
maintain a large array of characters (with gaps of empty elements). I can
be used to manage access to a remote share, where some pieces have been
retrieved, some have been requested, and others have not been read.
"""
def __init__(self, other=None):
self.spans = [] # (start, data) tuples, non-overlapping, merged
if other:
for (start, data) in other.get_chunks():
self.add(start, data)
def __len__(self):
# return number of bytes we're holding
return sum([len(data) for (start,data) in self.spans])
def _dump(self):
# return iterator of sorted list of offsets, one per byte
for (start,data) in self.spans:
for i in range(start, start+len(data)):
yield i
def dump(self):
return "len=%d: %s" % (len(self),
",".join(["[%d-%d]" % (start,start+len(data)-1)
for (start,data) in self.spans]) )
def get_chunks(self):
return list(self.spans)
def get_spans(self):
"""Return a Spans object with a bit set for each byte I hold"""
return Spans([(start, len(data)) for (start,data) in self.spans])
def assert_invariants(self):
if not self.spans:
return
prev_start = self.spans[0][0]
prev_end = prev_start + len(self.spans[0][1])
for start, data in self.spans[1:]:
if not start > prev_end:
# adjacent or overlapping: bad
print "ASSERTION FAILED", self.spans
raise AssertionError
def get(self, start, length):
# returns a string of LENGTH, or None
#print "get", start, length, self.spans
end = start+length
for (s_start,s_data) in self.spans:
s_end = s_start+len(s_data)
#print " ",s_start,s_end
if s_start <= start < s_end:
# we want some data from this span. Because we maintain
# strictly merged and non-overlapping spans, everything we
# want must be in this span.
offset = start - s_start
if offset + length > len(s_data):
#print " None, span falls short"
return None # span falls short
#print " some", s_data[offset:offset+length]
return s_data[offset:offset+length]
if s_start >= end:
# we've gone too far: no further spans will overlap
#print " None, gone too far"
return None
#print " None, ran out of spans"
return None
def add(self, start, data):
# first: walk through existing spans, find overlap, modify-in-place
# create list of new spans
# add new spans
# sort
# merge adjacent spans
#print "add", start, data, self.spans
end = start + len(data)
i = 0
while len(data):
#print " loop", start, data, i, len(self.spans), self.spans
if i >= len(self.spans):
#print " append and done"
# append a last span
self.spans.append( (start, data) )
break
(s_start,s_data) = self.spans[i]
# five basic cases:
# a: OLD b:OLDD c1:OLD c2:OLD d1:OLDD d2:OLD e: OLLDD
# NEW NEW NEW NEWW NEW NEW NEW
#
# we handle A by inserting a new segment (with "N") and looping,
# turning it into B or C. We handle B by replacing a prefix and
# terminating. We handle C (both c1 and c2) by replacing the
# segment (and, for c2, looping, turning it into A). We handle D
# by replacing a suffix (and, for d2, looping, turning it into
# A). We handle E by replacing the middle and terminating.
if start < s_start:
# case A: insert a new span, then loop with the remainder
#print " insert new psan"
s_len = s_start-start
self.spans.insert(i, (start, data[:s_len]))
i += 1
start = s_start
data = data[s_len:]
continue
s_len = len(s_data)
s_end = s_start+s_len
if s_start <= start < s_end:
#print " modify this span", s_start, start, s_end
# we want to modify some data in this span: a prefix, a
# suffix, or the whole thing
if s_start == start:
if s_end <= end:
#print " replace whole segment"
# case C: replace this segment
self.spans[i] = (s_start, data[:s_len])
i += 1
start += s_len
data = data[s_len:]
# C2 is where len(data)>0
continue
# case B: modify the prefix, retain the suffix
#print " modify prefix"
self.spans[i] = (s_start, data + s_data[len(data):])
break
if start > s_start and end < s_end:
# case E: modify the middle
#print " modify middle"
prefix_len = start - s_start # we retain this much
suffix_len = s_end - end # and retain this much
newdata = s_data[:prefix_len] + data + s_data[-suffix_len:]
self.spans[i] = (s_start, newdata)
break
# case D: retain the prefix, modify the suffix
#print " modify suffix"
prefix_len = start - s_start # we retain this much
suffix_len = s_len - prefix_len # we replace this much
#print " ", s_data, prefix_len, suffix_len, s_len, data
self.spans[i] = (s_start,
s_data[:prefix_len] + data[:suffix_len])
i += 1
start += suffix_len
data = data[suffix_len:]
#print " now", start, data
# D2 is where len(data)>0
continue
# else we're not there yet
#print " still looking"
i += 1
continue
# now merge adjacent spans
#print " merging", self.spans
newspans = []
for (s_start,s_data) in self.spans:
if newspans and adjacent(newspans[-1][0], len(newspans[-1][1]),
s_start, len(s_data)):
newspans[-1] = (newspans[-1][0], newspans[-1][1] + s_data)
else:
newspans.append( (s_start, s_data) )
self.spans = newspans
self.assert_invariants()
#print " done", self.spans
def remove(self, start, length):
i = 0
end = start + length
#print "remove", start, length, self.spans
while i < len(self.spans):
(s_start,s_data) = self.spans[i]
if s_start >= end:
# this segment is entirely right of the removed region, and
# all further segments are even further right. We're done.
break
s_len = len(s_data)
s_end = s_start + s_len
o = overlap(start, length, s_start, s_len)
if not o:
i += 1
continue
o_start, o_len = o
o_end = o_start + o_len
if o_len == s_len:
# remove the whole segment
del self.spans[i]
continue
if o_start == s_start:
# remove a prefix, leaving the suffix from o_end to s_end
prefix_len = o_end - o_start
self.spans[i] = (o_end, s_data[prefix_len:])
i += 1
continue
elif o_end == s_end:
# remove a suffix, leaving the prefix from s_start to o_start
prefix_len = o_start - s_start
self.spans[i] = (s_start, s_data[:prefix_len])
i += 1
continue
# remove the middle, creating a new segment
# left is s_start:o_start, right is o_end:s_end
left_len = o_start - s_start
left = s_data[:left_len]
right_len = s_end - o_end
right = s_data[-right_len:]
self.spans[i] = (s_start, left)
self.spans.insert(i+1, (o_end, right))
break
#print " done", self.spans
def pop(self, start, length):
data = self.get(start, length)
if data:
self.remove(start, length)
return data