repoview: separate cache hash computation from cache reading

This change will make it easier for extensions to use another cache hash.

mercurial/repoview.py

@@ -1,360 +1,363
 # repoview.py - Filtered view of a localrepo object
 #
 # Copyright 2012 Pierre-Yves David <[e-mail]>
 #                Logilab SA        <[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 __future__ import absolute_import
 
 import copy
 import hashlib
 import heapq
 import struct
 
 from .node import nullrev
 from . import (
     error,
     obsolete,
     phases,
     tags as tagsmod,
 )
 
 def hideablerevs(repo):
     """Revision candidates to be hidden
 
     This is a standalone function to allow extensions to wrap it.
 
     Because we use the set of immutable changesets as a fallback subset in
     branchmap (see mercurial.branchmap.subsettable), you cannot set "public"
     changesets as "hideable". Doing so would break multiple code assertions and
     lead to crashes."""
     return obsolete.getrevs(repo, 'obsolete')
 
 def _getstatichidden(repo):
     """Revision to be hidden (disregarding dynamic blocker)
 
     To keep a consistent graph, we cannot hide any revisions with
     non-hidden descendants. This function computes the set of
     revisions that could be hidden while keeping the graph consistent.
 
     A second pass will be done to apply "dynamic blocker" like bookmarks or
     working directory parents.
 
     """
     assert not repo.changelog.filteredrevs
     hidden = set(hideablerevs(repo))
     if hidden:
         getphase = repo._phasecache.phase
         getparentrevs = repo.changelog.parentrevs
         # Skip heads which are public (guaranteed to not be hidden)
         heap = [-r for r in repo.changelog.headrevs() if getphase(repo, r)]
         heapq.heapify(heap)
         heappop = heapq.heappop
         heappush = heapq.heappush
         seen = set() # no need to init it with heads, they have no children
         while heap:
             rev = -heappop(heap)
             # All children have been processed so at that point, if no children
             # removed 'rev' from the 'hidden' set, 'rev' is going to be hidden.
             blocker = rev not in hidden
             for parent in getparentrevs(rev):
                 if parent == nullrev:
                     continue
                 if blocker:
                     # If visible, ensure parent will be visible too
                     hidden.discard(parent)
                 # - Avoid adding the same revision twice
                 # - Skip nodes which are public (guaranteed to not be hidden)
                 pre = len(seen)
                 seen.add(parent)
                 if pre < len(seen) and getphase(repo, rev):
                     heappush(heap, -parent)
     return hidden
 
 def _getdynamicblockers(repo):
     """Non-cacheable revisions blocking hidden changesets from being filtered.
 
     Get revisions that will block hidden changesets and are likely to change,
     but unlikely to create hidden blockers. They won't be cached, so be careful
     with adding additional computation."""
 
     cl = repo.changelog
     blockers = set()
     blockers.update([par.rev() for par in repo[None].parents()])
     blockers.update([cl.rev(bm) for bm in repo._bookmarks.values()])
 
     tags = {}
     tagsmod.readlocaltags(repo.ui, repo, tags, {})
     if tags:
         rev, nodemap = cl.rev, cl.nodemap
         blockers.update(rev(t[0]) for t in tags.values() if t[0] in nodemap)
     return blockers
 
 cacheversion = 1
 cachefile = 'cache/hidden'
 
 def cachehash(repo, hideable):
     """return sha1 hash of repository data to identify a valid cache.
 
     We calculate a sha1 of repo heads and the content of the obsstore and write
     it to the cache. Upon reading we can easily validate by checking the hash
     against the stored one and discard the cache in case the hashes don't match.
     """
     h = hashlib.sha1()
     h.update(''.join(repo.heads()))
     h.update(str(hash(frozenset(hideable))))
     return h.digest()
 
 def _writehiddencache(cachefile, cachehash, hidden):
     """write hidden data to a cache file"""
     data = struct.pack('>%ii' % len(hidden), *sorted(hidden))
     cachefile.write(struct.pack(">H", cacheversion))
     cachefile.write(cachehash)
     cachefile.write(data)
 
 def trywritehiddencache(repo, hideable, hidden):
     """write cache of hidden changesets to disk
 
     Will not write the cache if a wlock cannot be obtained lazily.
     The cache consists of a head of 22byte:
        2 byte    version number of the cache
       20 byte    sha1 to validate the cache
      n*4 byte    hidden revs
     """
     wlock = fh = None
     try:
         wlock = repo.wlock(wait=False)
         # write cache to file
         newhash = cachehash(repo, hideable)
         fh = repo.vfs.open(cachefile, 'w+b', atomictemp=True)
         _writehiddencache(fh, newhash, hidden)
         fh.close()
     except (IOError, OSError):
         repo.ui.debug('error writing hidden changesets cache\n')
     except error.LockHeld:
         repo.ui.debug('cannot obtain lock to write hidden changesets cache\n')
     finally:
         if wlock:
             wlock.release()
 
-def tryreadcache(repo, hideable):
-    """read a cache if the cache exists and is valid, otherwise returns None."""
+def _readhiddencache(repo, cachefilename, newhash):
     hidden = fh = None
     try:
         if repo.vfs.exists(cachefile):
             fh = repo.vfs.open(cachefile, 'rb')
             version, = struct.unpack(">H", fh.read(2))
             oldhash = fh.read(20)
-            newhash = cachehash(repo, hideable)
             if (cacheversion, oldhash) == (version, newhash):
                 # cache is valid, so we can start reading the hidden revs
                 data = fh.read()
                 count = len(data) / 4
                 hidden = frozenset(struct.unpack('>%ii' % count, data))
         return hidden
     except struct.error:
         repo.ui.debug('corrupted hidden cache\n')
         # No need to fix the content as it will get rewritten
         return None
     except (IOError, OSError):
         repo.ui.debug('cannot read hidden cache\n')
         return None
     finally:
         if fh:
             fh.close()
 
+def tryreadcache(repo, hideable):
+    """read a cache if the cache exists and is valid, otherwise returns None."""
+    newhash = cachehash(repo, hideable)
+    return _readhiddencache(repo, cachefile, newhash)
+
 def computehidden(repo):
     """compute the set of hidden revision to filter
 
     During most operation hidden should be filtered."""
     assert not repo.changelog.filteredrevs
 
     hidden = frozenset()
     hideable = hideablerevs(repo)
     if hideable:
         cl = repo.changelog
         hidden = tryreadcache(repo, hideable)
         if hidden is None:
             hidden = frozenset(_getstatichidden(repo))
             trywritehiddencache(repo, hideable, hidden)
 
         # check if we have wd parents, bookmarks or tags pointing to hidden
         # changesets and remove those.
         dynamic = hidden & _getdynamicblockers(repo)
         if dynamic:
             blocked = cl.ancestors(dynamic, inclusive=True)
             hidden = frozenset(r for r in hidden if r not in blocked)
     return hidden
 
 def computeunserved(repo):
     """compute the set of revision that should be filtered when used a server
 
     Secret and hidden changeset should not pretend to be here."""
     assert not repo.changelog.filteredrevs
     # fast path in simple case to avoid impact of non optimised code
     hiddens = filterrevs(repo, 'visible')
     if phases.hassecret(repo):
         cl = repo.changelog
         secret = phases.secret
         getphase = repo._phasecache.phase
         first = min(cl.rev(n) for n in repo._phasecache.phaseroots[secret])
         revs = cl.revs(start=first)
         secrets = set(r for r in revs if getphase(repo, r) >= secret)
         return frozenset(hiddens | secrets)
     else:
         return hiddens
 
 def computemutable(repo):
     """compute the set of revision that should be filtered when used a server
 
     Secret and hidden changeset should not pretend to be here."""
     assert not repo.changelog.filteredrevs
     # fast check to avoid revset call on huge repo
     if any(repo._phasecache.phaseroots[1:]):
         getphase = repo._phasecache.phase
         maymutable = filterrevs(repo, 'base')
         return frozenset(r for r in maymutable if getphase(repo, r))
     return frozenset()
 
 def computeimpactable(repo):
     """Everything impactable by mutable revision
 
     The immutable filter still have some chance to get invalidated. This will
     happen when:
 
     - you garbage collect hidden changeset,
     - public phase is moved backward,
     - something is changed in the filtering (this could be fixed)
 
     This filter out any mutable changeset and any public changeset that may be
     impacted by something happening to a mutable revision.
 
     This is achieved by filtered everything with a revision number egal or
     higher than the first mutable changeset is filtered."""
     assert not repo.changelog.filteredrevs
     cl = repo.changelog
     firstmutable = len(cl)
     for roots in repo._phasecache.phaseroots[1:]:
         if roots:
             firstmutable = min(firstmutable, min(cl.rev(r) for r in roots))
     # protect from nullrev root
     firstmutable = max(0, firstmutable)
     return frozenset(xrange(firstmutable, len(cl)))
 
 # function to compute filtered set
 #
 # When adding a new filter you MUST update the table at:
 #     mercurial.branchmap.subsettable
 # Otherwise your filter will have to recompute all its branches cache
 # from scratch (very slow).
 filtertable = {'visible': computehidden,
                'served': computeunserved,
                'immutable':  computemutable,
                'base':  computeimpactable}
 
 def filterrevs(repo, filtername):
     """returns set of filtered revision for this filter name"""
     if filtername not in repo.filteredrevcache:
         func = filtertable[filtername]
         repo.filteredrevcache[filtername] = func(repo.unfiltered())
     return repo.filteredrevcache[filtername]
 
 class repoview(object):
     """Provide a read/write view of a repo through a filtered changelog
 
     This object is used to access a filtered version of a repository without
     altering the original repository object itself. We can not alter the
     original object for two main reasons:
     - It prevents the use of a repo with multiple filters at the same time. In
       particular when multiple threads are involved.
     - It makes scope of the filtering harder to control.
 
     This object behaves very closely to the original repository. All attribute
     operations are done on the original repository:
     - An access to `repoview.someattr` actually returns `repo.someattr`,
     - A write to `repoview.someattr` actually sets value of `repo.someattr`,
     - A deletion of `repoview.someattr` actually drops `someattr`
       from `repo.__dict__`.
 
     The only exception is the `changelog` property. It is overridden to return
     a (surface) copy of `repo.changelog` with some revisions filtered. The
     `filtername` attribute of the view control the revisions that need to be
     filtered.  (the fact the changelog is copied is an implementation detail).
 
     Unlike attributes, this object intercepts all method calls. This means that
     all methods are run on the `repoview` object with the filtered `changelog`
     property. For this purpose the simple `repoview` class must be mixed with
     the actual class of the repository. This ensures that the resulting
     `repoview` object have the very same methods than the repo object. This
     leads to the property below.
 
         repoview.method() --> repo.__class__.method(repoview)
 
     The inheritance has to be done dynamically because `repo` can be of any
     subclasses of `localrepo`. Eg: `bundlerepo` or `statichttprepo`.
     """
 
     def __init__(self, repo, filtername):
         object.__setattr__(self, '_unfilteredrepo', repo)
         object.__setattr__(self, 'filtername', filtername)
         object.__setattr__(self, '_clcachekey', None)
         object.__setattr__(self, '_clcache', None)
 
     # not a propertycache on purpose we shall implement a proper cache later
     @property
     def changelog(self):
         """return a filtered version of the changeset
 
         this changelog must not be used for writing"""
         # some cache may be implemented later
         unfi = self._unfilteredrepo
         unfichangelog = unfi.changelog
         # bypass call to changelog.method
         unfiindex = unfichangelog.index
         unfilen = len(unfiindex) - 1
         unfinode = unfiindex[unfilen - 1][7]
 
         revs = filterrevs(unfi, self.filtername)
         cl = self._clcache
         newkey = (unfilen, unfinode, hash(revs), unfichangelog._delayed)
         # if cl.index is not unfiindex, unfi.changelog would be
         # recreated, and our clcache refers to garbage object
         if (cl is not None and
             (cl.index is not unfiindex or newkey != self._clcachekey)):
             cl = None
         # could have been made None by the previous if
         if cl is None:
             cl = copy.copy(unfichangelog)
             cl.filteredrevs = revs
             object.__setattr__(self, '_clcache', cl)
             object.__setattr__(self, '_clcachekey', newkey)
         return cl
 
     def unfiltered(self):
         """Return an unfiltered version of a repo"""
         return self._unfilteredrepo
 
     def filtered(self, name):
         """Return a filtered version of a repository"""
         if name == self.filtername:
             return self
         return self.unfiltered().filtered(name)
 
     # everything access are forwarded to the proxied repo
     def __getattr__(self, attr):
         return getattr(self._unfilteredrepo, attr)
 
     def __setattr__(self, attr, value):
         return setattr(self._unfilteredrepo, attr, value)
 
     def __delattr__(self, attr):
         return delattr(self._unfilteredrepo, attr)
 
     # The `requirements` attribute is initialized during __init__. But
     # __getattr__ won't be called as it also exists on the class. We need
     # explicit forwarding to main repo here
     @property
     def requirements(self):
         return self._unfilteredrepo.requirements