mercurial/repoview.py

revlog: use existing file handle when reading during _addrevision

_addrevision() may need to read from revlogs as part of computing
deltas. Previously, we would flush existing file handles and open
a new, short-lived file handle to perform the reading.

If we have an existing file handle, it seems logical to reuse it
for reading instead of opening a new file handle. This patch
makes that the new behavior.

After this patch, revlog files are only reopened when adding
revisions if the revlog is switched from inline to non-inline.

On Linux when unbundling a bundle of the mozilla-central repo, this
patch has the following impact on system call counts:

Call     Before     After       Delta
write    827,639    673,390   -154,249
open     700,103    684,089    -16,014
read      74,489     74,489          0
fstat    493,924    461,896    -32,028
close    249,131    233,117    -16,014
stat     242,001    242,001          0
lstat     18,676     18,676          0
lseek     20,268     20,268          0
ioctl     14,652     13,173     -1,479
TOTAL  3,180,758  2,930,679   -250,079

It's worth noting that many of the open() calls fail due to missing
files. That's why there are many more open() calls than close().

Despite the significant system call reduction, this change does not
seem to have a significant performance impact on Linux.

On Windows 10 (not a VM, on a SSD), this patch appears to reduce
unbundle time for mozilla-central from ~960s to ~920s. This isn't
as significant as I was hoping. But a decrease it is nonetheless.
Still, Windows unbundle performance is still >2x slower than Linux.

Despite the lack of significant gains, fewer system calls is fewer
system calls. If nothing else, this will narrow the focus of potential
areas to optimize in the future.

# 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 heapq
import struct

from .node import nullrev
from . import (
    error,
    obsolete,
    phases,
    tags as tagsmod,
    util,
)

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 _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 = util.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)
    except (IOError, OSError):
        repo.ui.debug('error writing hidden changesets cache')
    except error.LockHeld:
        repo.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
        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
        revs = filterrevs(unfi, self.filtername)
        cl = self._clcache
        newkey = (len(unfichangelog), unfichangelog.tip(), hash(revs),
                  unfichangelog._delayed)
        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.filteredrevs = ()  # disable filtering for tip
                curkey = (len(cl), cl.tip(), hash(oldfilter), cl._delayed)
            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