repoview: add caching bits

Add a caching infrastructure to cache hidden changesets. The cache tries to read
the cache lazily and falls back to recomputing if no wlock can be obtain.
To validate the cache we store a sha of the obstore content and repo heads in
the beginning of the cache which we check every request.

mercurial/repoview.py

@@ -1,250 +1,317 b''
 # 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.
 
 import copy
+import error
+import hashlib
 import phases
 import util
 import obsolete
+import struct
 import tags as tagsmod
-
+from mercurial.i18n import _
 
 def hideablerevs(repo):
     """Revisions candidates to be hidden
 
     This is a standalone function to help extensions to wrap it."""
     return obsolete.getrevs(repo, 'obsolete')
 
 def _getstaticblockers(repo):
     """Cacheable revisions blocking hidden changesets from being filtered.
 
     Additional non-cached hidden blockers are computed in _getdynamicblockers.
     This is a standalone function to help extensions to wrap it."""
     assert not repo.changelog.filteredrevs
     hideable = hideablerevs(repo)
     blockers = set()
     if hideable:
         # We use cl to avoid recursive lookup from repo[xxx]
         cl = repo.changelog
         firsthideable = min(hideable)
         revs = cl.revs(start=firsthideable)
         tofilter = repo.revs(
             '(%ld) and children(%ld)', list(revs), list(hideable))
         blockers.update([r for r in tofilter if r not in hideable])
     return blockers
 
 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 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)
+        sortedset = sorted(hidden)
+        data = struct.pack('>%iI' % len(sortedset), *sortedset)
+        fh = repo.vfs.open(cachefile, 'w+b', atomictemp=True)
+        fh.write(struct.pack(">H", cacheversion))
+        fh.write(newhash)
+        fh.write(data)
+    except (IOError, OSError):
+        ui.debug('error writing hidden changesets cache')
+    except error.LockHeld:
+        ui.debug('cannot obtain lock to write hidden changesets cache')
+    finally:
+        if fh:
+            fh.close()
+        if wlock:
+            wlock.release()
+
+def tryreadcache(repo, hideable):
+    """read a cache if the cache exists and is valid, otherwise returns None."""
+    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
+    finally:
+        if fh:
+            fh.close()
+
 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
         blocked = cl.ancestors(_getstaticblockers(repo), inclusive=True)
         hidden = frozenset(r for r in hideable if r not in blocked)
 
         # 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 util.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
         revs = filterrevs(unfi, self.filtername)
         cl = self._clcache
         newkey = (len(unfichangelog), unfichangelog.tip(), hash(revs))
         if cl is not None:
             # we need to check curkey too for some obscure reason.
             # MQ test show a corruption of the underlying repo (in _clcache)
             # without change in the cachekey.
             oldfilter = cl.filteredrevs
             try:
                 cl.filterrevs = ()  # disable filtering for tip
                 curkey = (len(cl), cl.tip(), hash(oldfilter))
             finally:
                 cl.filteredrevs = oldfilter
             if newkey != self._clcachekey or newkey != curkey:
                 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