Mercurial > hg
view mercurial/peer.py @ 29322:66dbdd3cc2b9 stable
bdiff: extend matches across popular lines
For very large diffs that have large numbers of identical lines (JSON
dumps) that also have large blocks of identical text, bdiff could become
confused about which block matches which because it can only match
very limited regions. The result is very large diffs for small sets of edits.
The earlier recursion rebalancing fix made this behavior more frequent because
it's now more prone to match block 1 to block 2. One frequent user of
large JSON files reported being unable to pass the resulting diffs
through their code review system.
Prior to this change, bdiff would calculate the length of a match at
(i, j) as 1 + length found at (i-1, j-1). With large number of popular
(ignored) lines, this often meant matches couldn't be extended
backwards at all and thus all matching regions were very small.
Disabling the popularity threshold is not an option because it brings
back quadratic behavior.
Instead, we extend a match backwards until we either found a previously
discovered match or we find a mismatching line. This thus successfully
bridges over any popular lines inside and before a matching region.
The larger regions then significant reduce the probability of confusion.
author | Matt Mackall <mpm@selenic.com> |
---|---|
date | Thu, 02 Jun 2016 17:09:06 -0500 |
parents | 8d38eab2777a |
children | ead25aa27a43 |
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# peer.py - repository base classes for mercurial # # Copyright 2005, 2006 Matt Mackall <mpm@selenic.com> # Copyright 2006 Vadim Gelfer <vadim.gelfer@gmail.com> # # This software may be used and distributed according to the terms of the # GNU General Public License version 2 or any later version. from __future__ import absolute_import from .i18n import _ from . import ( error, util, ) # abstract batching support class future(object): '''placeholder for a value to be set later''' def set(self, value): if util.safehasattr(self, 'value'): raise error.RepoError("future is already set") self.value = value class batcher(object): '''base class for batches of commands submittable in a single request All methods invoked on instances of this class are simply queued and return a a future for the result. Once you call submit(), all the queued calls are performed and the results set in their respective futures. ''' def __init__(self): self.calls = [] def __getattr__(self, name): def call(*args, **opts): resref = future() self.calls.append((name, args, opts, resref,)) return resref return call def submit(self): raise NotImplementedError() class iterbatcher(batcher): def submit(self): raise NotImplementedError() def results(self): raise NotImplementedError() class localbatch(batcher): '''performs the queued calls directly''' def __init__(self, local): batcher.__init__(self) self.local = local def submit(self): for name, args, opts, resref in self.calls: resref.set(getattr(self.local, name)(*args, **opts)) class localiterbatcher(iterbatcher): def __init__(self, local): super(iterbatcher, self).__init__() self.local = local def submit(self): # submit for a local iter batcher is a noop pass def results(self): for name, args, opts, resref in self.calls: yield getattr(self.local, name)(*args, **opts) def batchable(f): '''annotation for batchable methods Such methods must implement a coroutine as follows: @batchable def sample(self, one, two=None): # Handle locally computable results first: if not one: yield "a local result", None # Build list of encoded arguments suitable for your wire protocol: encargs = [('one', encode(one),), ('two', encode(two),)] # Create future for injection of encoded result: encresref = future() # Return encoded arguments and future: yield encargs, encresref # Assuming the future to be filled with the result from the batched # request now. Decode it: yield decode(encresref.value) The decorator returns a function which wraps this coroutine as a plain method, but adds the original method as an attribute called "batchable", which is used by remotebatch to split the call into separate encoding and decoding phases. ''' def plain(*args, **opts): batchable = f(*args, **opts) encargsorres, encresref = batchable.next() if not encresref: return encargsorres # a local result in this case self = args[0] encresref.set(self._submitone(f.func_name, encargsorres)) return batchable.next() setattr(plain, 'batchable', f) return plain class peerrepository(object): def batch(self): return localbatch(self) def iterbatch(self): """Batch requests but allow iterating over the results. This is to allow interleaving responses with things like progress updates for clients. """ return localiterbatcher(self) def capable(self, name): '''tell whether repo supports named capability. return False if not supported. if boolean capability, return True. if string capability, return string.''' caps = self._capabilities() if name in caps: return True name_eq = name + '=' for cap in caps: if cap.startswith(name_eq): return cap[len(name_eq):] return False def requirecap(self, name, purpose): '''raise an exception if the given capability is not present''' if not self.capable(name): raise error.CapabilityError( _('cannot %s; remote repository does not ' 'support the %r capability') % (purpose, name)) def local(self): '''return peer as a localrepo, or None''' return None def peer(self): return self def canpush(self): return True def close(self): pass