comparison mercurial/tags.py @ 9151:f528d1a93491

tags: implement persistent tag caching (issue548).

- rename findglobaltags() to findglobaltags1() (so the "no cache"
  implementation is still there if we need it)
- add findglobaltags2() and make findglobaltags() an alias for it
  (disabling tag caching is a one-line patch)
- factor out tagcache class with methods readcache() and writecache();
  the expensive part of tag finding (iterate over heads and find
  .hgtags filenode) is now in tagcache.readcache()

9150:09a1ee498756

# Copyright 2009 Greg Ward <[e-mail]>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2, incorporated herein by reference.

# Currently this module only deals with reading tags.  Soon it will grow
# support for caching tag info.  Eventually, it could take care of
# updating (adding/removing/moving) tags too.

from node import bin, hex
from i18n import _
import encoding
import error

def findglobaltags(ui, repo, alltags, tagtypes):
    '''Find global tags in repo by reading .hgtags from every head that
    has a distinct version of it.  Updates the dicts alltags, tagtypes
    in place: alltags maps tag name to (node, hist) pair (see _readtags()
    below), and tagtypes maps tag name to tag type ('global' in this
    case).'''

    # read the tags file from each head, ending with the tip
    for fctx in reversed(ctxs):
        filetags = _readtags(
            ui, repo, fctx.data().splitlines(), fctx)
        _updatetags(filetags, "global", alltags, tagtypes)

def readlocaltags(ui, repo, alltags, tagtypes):
    '''Read local tags in repo.  Update alltags and tagtypes.'''
    try:
        data = encoding.fromlocal(repo.opener("localtags").read())

            anode = bnode
        ahist.extend([n for n in bhist if n not in ahist])
        alltags[name] = anode, ahist
        tagtypes[name] = tagtype

9151:f528d1a93491

# Copyright 2009 Greg Ward <[e-mail]>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2, incorporated herein by reference.

# Currently this module only deals with reading and caching tags.
# Eventually, it could take care of updating (adding/removing/moving)
# tags too.

import os
from node import nullid, bin, hex, short
from i18n import _
import encoding
import error

def _debugalways(ui, *msg):
    ui.write(*msg)

def _debugconditional(ui, *msg):
    ui.debug(*msg)

def _debugnever(ui, *msg):
    pass

_debug = _debugalways
_debug = _debugnever

def findglobaltags1(ui, repo, alltags, tagtypes):
    '''Find global tags in repo by reading .hgtags from every head that
    has a distinct version of it.  Updates the dicts alltags, tagtypes
    in place: alltags maps tag name to (node, hist) pair (see _readtags()
    below), and tagtypes maps tag name to tag type ('global' in this
    case).'''

    # read the tags file from each head, ending with the tip
    for fctx in reversed(ctxs):
        filetags = _readtags(
            ui, repo, fctx.data().splitlines(), fctx)
        _updatetags(filetags, "global", alltags, tagtypes)

def findglobaltags2(ui, repo, alltags, tagtypes):
    '''Same as findglobaltags1(), but with caching.'''
    (heads, tagfnode, shouldwrite) = _readtagcache(ui, repo)

    _debug(ui, "reading tags from %d head(s): %s\n"
           % (len(heads), map(short, reversed(heads))))
    seen = set()                    # set of fnode
    fctx = None
    for head in reversed(heads):        # oldest to newest
        assert head in repo.changelog.nodemap, \
               "tag cache returned bogus head %s" % short(head)

        fnode = tagfnode.get(head)
        if fnode and fnode not in seen:
            seen.add(fnode)
            if not fctx:
                fctx = repo.filectx('.hgtags', fileid=fnode)
            else:
                fctx = fctx.filectx(fnode)

            filetags = _readtags(ui, repo, fctx.data().splitlines(), fctx)
            _updatetags(filetags, 'global', alltags, tagtypes)

    # and update the cache (if necessary)
    if shouldwrite:
        _writetagcache(ui, repo, heads, tagfnode)

# Set this to findglobaltags1 to disable tag caching.
findglobaltags = findglobaltags2

def readlocaltags(ui, repo, alltags, tagtypes):
    '''Read local tags in repo.  Update alltags and tagtypes.'''
    try:
        data = encoding.fromlocal(repo.opener("localtags").read())

            anode = bnode
        ahist.extend([n for n in bhist if n not in ahist])
        alltags[name] = anode, ahist
        tagtypes[name] = tagtype


# The tag cache only stores info about heads, not the tag contents
# from each head.  I.e. it doesn't try to squeeze out the maximum
# performance, but is simpler has a better chance of actually
# working correctly.  And this gives the biggest performance win: it
# avoids looking up .hgtags in the manifest for every head, and it
# can avoid calling heads() at all if there have been no changes to
# the repo.

def _readtagcache(ui, repo):
    '''Read the tag cache and return a tuple (heads, fnodes,
    shouldwrite).  heads is the list of all heads currently in the
    repository (ordered from tip to oldest) and fnodes is a mapping from
    head to .hgtags filenode.  Caller is responsible for reading tag
    info from each head.'''

    try:
        cachefile = repo.opener('tags.cache', 'r')
        _debug(ui, 'reading tag cache from %s\n' % cachefile.name)
    except IOError:
        cachefile = None

    # The cache file consists of lines like
    #   <headrev> <headnode> [<tagnode>]
    # where <headrev> and <headnode> redundantly identify a repository
    # head from the time the cache was written, and <tagnode> is the
    # filenode of .hgtags on that head.  Heads with no .hgtags file will
    # have no <tagnode>.  The cache is ordered from tip to oldest (which
    # is part of why <headrev> is there: a quick visual check is all
    # that's required to ensure correct order).
    # 
    # This information is enough to let us avoid the most expensive part
    # of finding global tags, which is looking up <tagnode> in the
    # manifest for each head.
    cacherevs = []                      # list of headrev
    cacheheads = []                     # list of headnode
    cachefnode = {}                     # map headnode to filenode
    if cachefile:
        for line in cachefile:
            line = line.rstrip().split()
            cacherevs.append(int(line[0]))
            headnode = bin(line[1])
            cacheheads.append(headnode)
            if len(line) == 3:
                fnode = bin(line[2])
                cachefnode[headnode] = fnode

        cachefile.close()

    tipnode = repo.changelog.tip()
    tiprev = len(repo.changelog) - 1

    # Case 1 (common): tip is the same, so nothing has changed.
    # (Unchanged tip trivially means no changesets have been added.
    # But, thanks to localrepository.destroyed(), it also means none
    # have been destroyed by strip or rollback.)
    if cacheheads and cacheheads[0] == tipnode and cacherevs[0] == tiprev:
        _debug(ui, "tag cache: tip unchanged\n")
        return (cacheheads, cachefnode, False)
        
    repoheads = repo.heads()

    # Case 2 (uncommon): empty repo; get out quickly and don't bother
    # writing an empty cache.
    if repoheads == [nullid]:
        return ([], {}, False)

    # Case 3 (uncommon): cache file missing or empty.
    if not cacheheads:
        _debug(ui, 'tag cache: cache file missing or empty\n')

    # Case 4 (uncommon): tip rev decreased.  This should only happen
    # when we're called from localrepository.destroyed().  Refresh the
    # cache so future invocations will not see disappeared heads in the
    # cache.
    elif cacheheads and tiprev < cacherevs[0]:
        _debug(ui,
               'tag cache: tip rev decremented (from %d to %d), '
               'so we must be destroying nodes\n'
               % (cacherevs[0], tiprev))

    # Case 5 (common): tip has changed, so we've added/replaced heads.
    else:
        _debug(ui,
               'tag cache: tip has changed (%d:%s); must find new heads\n'
               % (tiprev, short(tipnode)))

    # Luckily, the code to handle cases 3, 4, 5 is the same.  So the
    # above if/elif/else can disappear once we're confident this thing
    # actually works and we don't need the debug output.

    # N.B. in case 4 (nodes destroyed), "new head" really means "newly
    # exposed".
    newheads = [head
                for head in repoheads
                if head not in set(cacheheads)]
    _debug(ui, 'tag cache: found %d head(s) not in cache: %s\n'
           % (len(newheads), map(short, newheads)))

    # Now we have to lookup the .hgtags filenode for every new head.
    # This is the most expensive part of finding tags, so performance
    # depends primarily on the size of newheads.  Worst case: no cache
    # file, so newheads == repoheads.
    for head in newheads:
        cctx = repo[head]
        try:
            fnode = cctx.filenode('.hgtags')
            cachefnode[head] = fnode
        except error.LookupError:
            # no .hgtags file on this head
            pass

    # Caller has to iterate over all heads, but can use the filenodes in
    # cachefnode to get to each .hgtags revision quickly.
    return (repoheads, cachefnode, True)

def _writetagcache(ui, repo, heads, tagfnode):

    cachefile = repo.opener('tags.cache', 'w', atomictemp=True)
    _debug(ui, 'writing cache file %s\n' % cachefile.name)

    realheads = repo.heads()            # for sanity checks below
    for head in heads:
        # temporary sanity checks; these can probably be removed
        # once this code has been in crew for a few weeks
        assert head in repo.changelog.nodemap, \
               'trying to write non-existent node %s to tag cache' % short(head)
        assert head in realheads, \
               'trying to write non-head %s to tag cache' % short(head)
        assert head != nullid, \
               'trying to write nullid to tag cache'

        # This can't fail because of the first assert above.  When/if we
        # remove that assert, we might want to catch LookupError here
        # and downgrade it to a warning.
        rev = repo.changelog.rev(head)

        fnode = tagfnode.get(head)
        if fnode:
            cachefile.write('%d %s %s\n' % (rev, hex(head), hex(fnode)))
        else:
            cachefile.write('%d %s\n' % (rev, hex(head)))

    cachefile.rename()
    cachefile.close()