Mercurial > hg
annotate mercurial/pvec.py @ 34879:7d51a7792f52
subrepo: implement 'unshare' for Mercurial subrepos
I think there's a slight hole here in that a subrepo could be shared, removed
from .hgsub, and then it's not part of context.substate (so not iterated over).
But the push command has the same hole IIRC, and I think removing a subrepo is
an edge case.
The import hack is a copy/paste of subrepo.subrepo().
author | Matt Harbison <matt_harbison@yahoo.com> |
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date | Tue, 17 Oct 2017 22:55:33 -0400 |
parents | 4462a981e8df |
children | e7aa113b14f7 |
rev | line source |
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16249 | 1 # pvec.py - probabilistic vector clocks for Mercurial |
2 # | |
3 # Copyright 2012 Matt Mackall <mpm@selenic.com> | |
4 # | |
5 # This software may be used and distributed according to the terms of the | |
6 # GNU General Public License version 2 or any later version. | |
7 | |
8 ''' | |
9 A "pvec" is a changeset property based on the theory of vector clocks | |
10 that can be compared to discover relatedness without consulting a | |
11 graph. This can be useful for tasks like determining how a | |
12 disconnected patch relates to a repository. | |
13 | |
14 Currently a pvec consist of 448 bits, of which 24 are 'depth' and the | |
15 remainder are a bit vector. It is represented as a 70-character base85 | |
16 string. | |
17 | |
18 Construction: | |
19 | |
20 - a root changeset has a depth of 0 and a bit vector based on its hash | |
21 - a normal commit has a changeset where depth is increased by one and | |
22 one bit vector bit is flipped based on its hash | |
23 - a merge changeset pvec is constructed by copying changes from one pvec into | |
24 the other to balance its depth | |
25 | |
26 Properties: | |
27 | |
28 - for linear changes, difference in depth is always <= hamming distance | |
29 - otherwise, changes are probably divergent | |
30 - when hamming distance is < 200, we can reliably detect when pvecs are near | |
31 | |
32 Issues: | |
33 | |
34 - hamming distance ceases to work over distances of ~ 200 | |
35 - detecting divergence is less accurate when the common ancestor is very close | |
36 to either revision or total distance is high | |
37 - this could probably be improved by modeling the relation between | |
38 delta and hdist | |
39 | |
40 Uses: | |
41 | |
42 - a patch pvec can be used to locate the nearest available common ancestor for | |
43 resolving conflicts | |
44 - ordering of patches can be established without a DAG | |
45 - two head pvecs can be compared to determine whether push/pull/merge is needed | |
46 and approximately how many changesets are involved | |
47 - can be used to find a heuristic divergence measure between changesets on | |
48 different branches | |
49 ''' | |
50 | |
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51 from __future__ import absolute_import |
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52 |
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53 from .node import nullrev |
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54 from . import ( |
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55 util, |
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56 ) |
16249 | 57 |
58 _size = 448 # 70 chars b85-encoded | |
59 _bytes = _size / 8 | |
60 _depthbits = 24 | |
61 _depthbytes = _depthbits / 8 | |
62 _vecbytes = _bytes - _depthbytes | |
63 _vecbits = _vecbytes * 8 | |
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64 _radius = (_vecbits - 30) / 2 # high probability vectors are related |
16249 | 65 |
66 def _bin(bs): | |
67 '''convert a bytestring to a long''' | |
68 v = 0 | |
69 for b in bs: | |
70 v = v * 256 + ord(b) | |
71 return v | |
72 | |
73 def _str(v, l): | |
74 bs = "" | |
75 for p in xrange(l): | |
76 bs = chr(v & 255) + bs | |
77 v >>= 8 | |
78 return bs | |
79 | |
80 def _split(b): | |
81 '''depth and bitvec''' | |
82 return _bin(b[:_depthbytes]), _bin(b[_depthbytes:]) | |
83 | |
84 def _join(depth, bitvec): | |
85 return _str(depth, _depthbytes) + _str(bitvec, _vecbytes) | |
86 | |
87 def _hweight(x): | |
88 c = 0 | |
89 while x: | |
90 if x & 1: | |
91 c += 1 | |
92 x >>= 1 | |
93 return c | |
94 _htab = [_hweight(x) for x in xrange(256)] | |
95 | |
96 def _hamming(a, b): | |
97 '''find the hamming distance between two longs''' | |
98 d = a ^ b | |
99 c = 0 | |
100 while d: | |
101 c += _htab[d & 0xff] | |
102 d >>= 8 | |
103 return c | |
104 | |
105 def _mergevec(x, y, c): | |
106 # Ideally, this function would be x ^ y ^ ancestor, but finding | |
107 # ancestors is a nuisance. So instead we find the minimal number | |
108 # of changes to balance the depth and hamming distance | |
109 | |
110 d1, v1 = x | |
111 d2, v2 = y | |
112 if d1 < d2: | |
113 d1, d2, v1, v2 = d2, d1, v2, v1 | |
114 | |
115 hdist = _hamming(v1, v2) | |
116 ddist = d1 - d2 | |
117 v = v1 | |
118 m = v1 ^ v2 # mask of different bits | |
119 i = 1 | |
120 | |
121 if hdist > ddist: | |
122 # if delta = 10 and hdist = 100, then we need to go up 55 steps | |
123 # to the ancestor and down 45 | |
124 changes = (hdist - ddist + 1) / 2 | |
125 else: | |
126 # must make at least one change | |
127 changes = 1 | |
128 depth = d1 + changes | |
129 | |
130 # copy changes from v2 | |
131 if m: | |
132 while changes: | |
133 if m & i: | |
134 v ^= i | |
135 changes -= 1 | |
136 i <<= 1 | |
137 else: | |
138 v = _flipbit(v, c) | |
139 | |
140 return depth, v | |
141 | |
142 def _flipbit(v, node): | |
143 # converting bit strings to longs is slow | |
144 bit = (hash(node) & 0xffffffff) % _vecbits | |
145 return v ^ (1<<bit) | |
146 | |
147 def ctxpvec(ctx): | |
148 '''construct a pvec for ctx while filling in the cache''' | |
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149 r = ctx.repo() |
16249 | 150 if not util.safehasattr(r, "_pveccache"): |
151 r._pveccache = {} | |
152 pvc = r._pveccache | |
153 if ctx.rev() not in pvc: | |
154 cl = r.changelog | |
155 for n in xrange(ctx.rev() + 1): | |
156 if n not in pvc: | |
157 node = cl.node(n) | |
158 p1, p2 = cl.parentrevs(n) | |
159 if p1 == nullrev: | |
160 # start with a 'random' vector at root | |
161 pvc[n] = (0, _bin((node * 3)[:_vecbytes])) | |
162 elif p2 == nullrev: | |
163 d, v = pvc[p1] | |
164 pvc[n] = (d + 1, _flipbit(v, node)) | |
165 else: | |
166 pvc[n] = _mergevec(pvc[p1], pvc[p2], node) | |
167 bs = _join(*pvc[ctx.rev()]) | |
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168 return pvec(util.b85encode(bs)) |
16249 | 169 |
170 class pvec(object): | |
171 def __init__(self, hashorctx): | |
172 if isinstance(hashorctx, str): | |
173 self._bs = hashorctx | |
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174 self._depth, self._vec = _split(util.b85decode(hashorctx)) |
16249 | 175 else: |
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176 self._vec = ctxpvec(hashorctx) |
16249 | 177 |
178 def __str__(self): | |
179 return self._bs | |
180 | |
181 def __eq__(self, b): | |
182 return self._vec == b._vec and self._depth == b._depth | |
183 | |
184 def __lt__(self, b): | |
185 delta = b._depth - self._depth | |
186 if delta < 0: | |
187 return False # always correct | |
188 if _hamming(self._vec, b._vec) > delta: | |
189 return False | |
190 return True | |
191 | |
192 def __gt__(self, b): | |
193 return b < self | |
194 | |
195 def __or__(self, b): | |
196 delta = abs(b._depth - self._depth) | |
197 if _hamming(self._vec, b._vec) <= delta: | |
198 return False | |
199 return True | |
200 | |
201 def __sub__(self, b): | |
202 if self | b: | |
203 raise ValueError("concurrent pvecs") | |
204 return self._depth - b._depth | |
205 | |
206 def distance(self, b): | |
207 d = abs(b._depth - self._depth) | |
208 h = _hamming(self._vec, b._vec) | |
209 return max(d, h) | |
210 | |
211 def near(self, b): | |
212 dist = abs(b.depth - self._depth) | |
213 if dist > _radius or _hamming(self._vec, b._vec) > _radius: | |
214 return False |