mercurial/dagutil.py

discovery: add new set-based discovery

Adds a new discovery method based on repeatedly sampling the still
undecided subset of the local node graph to determine the set of nodes
common to both the client and the server.

For small differences between client and server, it uses about the same
or slightly fewer roundtrips than the old tree-based discovery. For
larger differences, it typically reduces the number of roundtrips
drastically (from 150 to 4, for instance).

The old discovery code now lives in treediscovery.py, the new code is
in setdiscovery.py.

Still missing is a hook for extensions to contribute nodes to the
initial sample. For instance, Augie's remotebranches could contribute
the last known state of the server's heads.

Credits for the actual sampler and computing common heads instead of
bases go to Benoit Boissinot.

# dagutil.py - dag utilities for mercurial
#
# Copyright 2010 Benoit Boissinot <[e-mail]>
# and Peter Arrenbrecht <[e-mail]>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.

from node import nullrev


class basedag(object):
    '''generic interface for DAGs

    terms:
    "ix" (short for index) identifies a nodes internally,
    "id" identifies one externally.

    All params are ixs unless explicitly suffixed otherwise.
    Pluralized params are lists or sets.
    '''

    def __init__(self):
        self._inverse = None

    def nodeset(self):
        '''set of all node idxs'''
        raise NotImplementedError()

    def heads(self):
        '''list of head ixs'''
        raise NotImplementedError()

    def parents(self, ix):
        '''list of parents ixs of ix'''
        raise NotImplementedError()

    def inverse(self):
        '''inverse DAG, where parents becomes children, etc.'''
        raise NotImplementedError()

    def ancestorset(self, starts, stops=None):
        '''set of all ancestors of starts (incl), but stop walk at stops (excl)'''
        raise NotImplementedError()

    def descendantset(self, starts, stops=None):
        '''set of all descendants of starts (incl), but stop walk at stops (excl)'''
        return self.inverse().ancestorset(starts, stops)

    def headsetofconnecteds(self, ixs):
        '''subset of connected list of ixs so that no node has a descendant in it

        By "connected list" we mean that if an ancestor and a descendant are in
        the list, then so is at least one path connecting them.'''
        raise NotImplementedError()

    def externalize(self, ix):
        '''return a list of (or set if given a set) of node ids'''
        return self._externalize(ix)

    def externalizeall(self, ixs):
        '''return a list of (or set if given a set) of node ids'''
        ids = self._externalizeall(ixs)
        if isinstance(ixs, set):
            return set(ids)
        return list(ids)

    def internalize(self, id):
        '''return a list of (or set if given a set) of node ixs'''
        return self._internalize(id)

    def internalizeall(self, ids, filterunknown=False):
        '''return a list of (or set if given a set) of node ids'''
        ixs = self._internalizeall(ids, filterunknown)
        if isinstance(ids, set):
            return set(ixs)
        return list(ixs)


class genericdag(basedag):
    '''generic implementations for DAGs'''

    def ancestorset(self, starts, stops=None):
        stops = stops and set(stops) or set()
        seen = set()
        pending = list(starts)
        while pending:
            n = pending.pop()
            if n not in seen and n not in stops:
                seen.add(n)
                pending.extend(self.parents(n))
        return seen

    def headsetofconnecteds(self, ixs):
        hds = set(ixs)
        if not hds:
            return hds
        for n in ixs:
            for p in self.parents(n):
                hds.discard(p)
        assert hds
        return hds


class revlogbaseddag(basedag):
    '''generic dag interface to a revlog'''

    def __init__(self, revlog, nodeset):
        basedag.__init__(self)
        self._revlog = revlog
        self._heads = None
        self._nodeset = nodeset

    def nodeset(self):
        return self._nodeset

    def heads(self):
        if self._heads is None:
            self._heads = self._getheads()
        return self._heads

    def _externalize(self, ix):
        return self._revlog.index[ix][7]
    def _externalizeall(self, ixs):
        idx = self._revlog.index
        return [idx[i][7] for i in ixs]

    def _internalize(self, id):
        ix = self._revlog.rev(id)
        if ix == nullrev:
            raise LookupError(id, self._revlog.indexfile, _('nullid'))
        return ix
    def _internalizeall(self, ids, filterunknown):
        rl = self._revlog
        if filterunknown:
            return [r for r in map(rl.nodemap.get, ids)
                    if r is not None and r != nullrev]
        return map(self._internalize, ids)


class revlogdag(revlogbaseddag):
    '''dag interface to a revlog'''

    def __init__(self, revlog):
        revlogbaseddag.__init__(self, revlog, set(xrange(len(revlog))))

    def _getheads(self):
        return [r for r in self._revlog.headrevs() if r != nullrev]

    def parents(self, ix):
        rlog = self._revlog
        idx = rlog.index
        revdata = idx[ix]
        prev = revdata[5]
        if prev != nullrev:
            prev2 = revdata[6]
            if prev2 == nullrev:
                return [prev]
            return [prev, prev2]
        prev2 = revdata[6]
        if prev2 != nullrev:
            return [prev2]
        return []

    def inverse(self):
        if self._inverse is None:
            self._inverse = inverserevlogdag(self)
        return self._inverse

    def ancestorset(self, starts, stops=None):
        rlog = self._revlog
        idx = rlog.index
        stops = stops and set(stops) or set()
        seen = set()
        pending = list(starts)
        while pending:
            rev = pending.pop()
            if rev not in seen and rev not in stops:
                seen.add(rev)
                revdata = idx[rev]
                for i in [5, 6]:
                    prev = revdata[i]
                    if prev != nullrev:
                        pending.append(prev)
        return seen

    def headsetofconnecteds(self, ixs):
        if not ixs:
            return set()
        rlog = self._revlog
        idx = rlog.index
        headrevs = set(ixs)
        for rev in ixs:
            revdata = idx[rev]
            for i in [5, 6]:
                prev = revdata[i]
                if prev != nullrev:
                    headrevs.discard(prev)
        assert headrevs
        return headrevs


class inverserevlogdag(revlogbaseddag, genericdag):
    '''inverse of an existing revlog dag; see revlogdag.inverse()'''

    def __init__(self, orig):
        revlogbaseddag.__init__(self, orig._revlog, orig._nodeset)
        self._orig = orig
        self._children = {}
        self._roots = []
        self._walkfrom = len(self._revlog) - 1

    def _walkto(self, walkto):
        rev = self._walkfrom
        cs = self._children
        roots = self._roots
        idx = self._revlog.index
        while rev >= walkto:
            data = idx[rev]
            isroot = True
            for prev in [data[5], data[6]]: # parent revs
                if prev != nullrev:
                    cs.setdefault(prev, []).append(rev)
                    isroot = False
            if isroot:
                roots.append(rev)
            rev -= 1
        self._walkfrom = rev - 1

    def _getheads(self):
        self._walkto(nullrev)
        return self._roots

    def parents(self, ix):
        if ix is None:
            return []
        if ix <= self._walkfrom:
            self._walkto(ix)
        return self._children.get(ix, [])

    def inverse(self):
        return self._orig