view tests/drawdag.py @ 47010:76ae43d5b1db stable

repoview: fix memory leak of filtered repo classes

The leak occurs in long-running server processes with
extensions, and is measured at 110kB per request.

Before this change, the contents of the `_filteredrepotypes`
cache are not properly garbage collected, despite it begin
a `WeakKeyDictionary`.

Extensions have a tendency to generate a new repository class
for each `localrepo` instantiation. Server processes based
on `hgwebdir_mod` will instantiate a new `localrepo` for each
HTTP request that involves a repository.

As a result, with a testing process that repeatedly opens a
repository with several extensions activated
(`topic` notably among them), we see a steady increase in
resident memory of 110kB per repository instantiation before this
change. This is also true, if we call `gc.collect()` at each
instantiation, like `hgwebdir_mod` does, or not.

The cause of the leak is that the *values* aren't weak references.
This change uses `weakref.ref` for the values, and this makes
in our measurements the resident size increase drop to 5kB per
repository instantiation, with no explicit call of `gc.collect()`
at all.
There is currently no reason to believe that this remaining leak
of 5kB is related to or even due to Mercurial core.

We've also seen evidence that `ui.ui` instances weren't properly
garbage collected before the change (with the change, they are).
This could explain why the figures are relatively high.

In theory, the collection of weak references could lead to
much more misses in the cache, so we measured the impact on
the original case that was motivation for introducing that cache
in 7e89bd0cfb86 (see also issue5043): `hg convert` of the
mozilla-central repository. The bad news here is that there is a
major memory leak there, both with and without the present changeset.
There were no more cache misses, and we could see no
more memory leak with this change: the resident size after importing
roughly 100000 changesets was at 12.4GB before, and 12.5GB after.
The small increase is mentioned for completeness only, and we
believe that it should be ignored, at least as long as the main
leak isn't fixed. At less than 1% of the main leak, even finding out
whether it is merely noise would be wasteful.

Original context where this was spotted and first mitigated:
  https://foss.heptapod.net/heptapod/heptapod/-/issues/466

The leak reduction was also obtained in Heptapod inner HTTP server,
which amounts to the same as `hgwebdir_mod` for these questions.

The measurements done with Python 3.9, similar figures seen with 3.8.
More work on our side would be needed to give measurements with 2.7,
because of testing server process does not support it.

# drawdag.py - convert ASCII revision DAG to actual changesets
#
# Copyright 2016 Facebook, Inc.
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.
"""
create changesets from an ASCII graph for testing purpose.

For example, given the following input::

    c d
    |/
    b
    |
    a

4 changesets and 4 local tags will be created.
`hg log -G -T "{rev} {desc} (tag: {tags})"` will output::

    o  3 d (tag: d tip)
    |
    | o  2 c (tag: c)
    |/
    o  1 b (tag: b)
    |
    o  0 a (tag: a)

For root nodes (nodes without parents) in the graph, they can be revsets
pointing to existing nodes.  The ASCII graph could also have disconnected
components with same names referring to the same changeset.

Therefore, given the repo having the 4 changesets (and tags) above, with the
following ASCII graph as input::

    foo    bar       bar  foo
     |     /          |    |
    ancestor(c,d)     a   baz

The result (`hg log -G -T "{desc}"`) will look like::

    o    foo
    |\
    +---o  bar
    | | |
    | o |  baz
    |  /
    +---o  d
    | |
    +---o  c
    | |
    o |  b
    |/
    o  a

Note that if you take the above `hg log` output directly as input. It will work
as expected - the result would be an isomorphic graph::

    o    foo
    |\
    | | o  d
    | |/
    | | o  c
    | |/
    | | o  bar
    | |/|
    | o |  b
    | |/
    o /  baz
     /
    o  a

This is because 'o' is specially handled in the input: instead of using 'o' as
the node name, the word to the right will be used.

Some special comments could have side effects:

    - Create obsmarkers
      # replace: A -> B -> C -> D  # chained 1 to 1 replacements
      # split: A -> B, C           # 1 to many
      # prune: A, B, C             # many to nothing
"""
from __future__ import absolute_import, print_function

import collections
import itertools
import re

from mercurial.node import nullid
from mercurial.i18n import _
from mercurial import (
    context,
    error,
    obsolete,
    pycompat,
    registrar,
    scmutil,
    tags as tagsmod,
)

cmdtable = {}
command = registrar.command(cmdtable)

_pipechars = b'\\/+-|'
_nonpipechars = b''.join(
    pycompat.bytechr(i)
    for i in range(33, 127)
    if pycompat.bytechr(i) not in _pipechars
)


def _isname(ch):
    """char -> bool. return True if ch looks like part of a name, False
    otherwise"""
    return ch in _nonpipechars


def _parseasciigraph(text):
    r"""str -> {str : [str]}. convert the ASCII graph to edges

    >>> import pprint
    >>> pprint.pprint({pycompat.sysstr(k): [pycompat.sysstr(vv) for vv in v]
    ...  for k, v in _parseasciigraph(br'''
    ...        G
    ...        |
    ...  I D C F   # split: B -> E, F, G
    ...   \ \| |   # replace: C -> D -> H
    ...    H B E   # prune: F, I
    ...     \|/
    ...      A
    ... ''').items()})
    {'A': [],
     'B': ['A'],
     'C': ['B'],
     'D': ['B'],
     'E': ['A'],
     'F': ['E'],
     'G': ['F'],
     'H': ['A'],
     'I': ['H']}
    >>> pprint.pprint({pycompat.sysstr(k): [pycompat.sysstr(vv) for vv in v]
    ...  for k, v in _parseasciigraph(br'''
    ...  o    foo
    ...  |\
    ...  +---o  bar
    ...  | | |
    ...  | o |  baz
    ...  |  /
    ...  +---o  d
    ...  | |
    ...  +---o  c
    ...  | |
    ...  o |  b
    ...  |/
    ...  o  a
    ... ''').items()})
    {'a': [],
     'b': ['a'],
     'bar': ['b', 'a'],
     'baz': [],
     'c': ['b'],
     'd': ['b'],
     'foo': ['baz', 'b']}
    """
    lines = text.splitlines()
    edges = collections.defaultdict(list)  # {node: []}

    def get(y, x):
        """(int, int) -> char. give a coordinate, return the char. return a
        space for anything out of range"""
        if x < 0 or y < 0:
            return b' '
        try:
            return lines[y][x : x + 1] or b' '
        except IndexError:
            return b' '

    def getname(y, x):
        """(int, int) -> str. like get(y, x) but concatenate left and right
        parts. if name is an 'o', try to replace it to the right"""
        result = b''
        for i in itertools.count(0):
            ch = get(y, x - i)
            if not _isname(ch):
                break
            result = ch + result
        for i in itertools.count(1):
            ch = get(y, x + i)
            if not _isname(ch):
                break
            result += ch
        if result == b'o':
            # special handling, find the name to the right
            result = b''
            for i in itertools.count(2):
                ch = get(y, x + i)
                if ch == b' ' or ch in _pipechars:
                    if result or x + i >= len(lines[y]):
                        break
                else:
                    result += ch
            return result or b'o'
        return result

    def parents(y, x):
        """(int, int) -> [str]. follow the ASCII edges at given position,
        return a list of parents"""
        visited = {(y, x)}
        visit = []
        result = []

        def follow(y, x, expected):
            """conditionally append (y, x) to visit array, if it's a char
            in excepted. 'o' in expected means an '_isname' test.
            if '-' (or '+') is not in excepted, and get(y, x) is '-' (or '+'),
            the next line (y + 1, x) will be checked instead."""
            ch = get(y, x)
            if any(ch == c and c not in expected for c in (b'-', b'+')):
                y += 1
                return follow(y + 1, x, expected)
            if ch in expected or (b'o' in expected and _isname(ch)):
                visit.append((y, x))

        #  -o-  # starting point:
        #  /|\ # follow '-' (horizontally), and '/|\' (to the bottom)
        follow(y + 1, x, b'|')
        follow(y + 1, x - 1, b'/')
        follow(y + 1, x + 1, b'\\')
        follow(y, x - 1, b'-')
        follow(y, x + 1, b'-')

        while visit:
            y, x = visit.pop()
            if (y, x) in visited:
                continue
            visited.add((y, x))
            ch = get(y, x)
            if _isname(ch):
                result.append(getname(y, x))
                continue
            elif ch == b'|':
                follow(y + 1, x, b'/|o')
                follow(y + 1, x - 1, b'/')
                follow(y + 1, x + 1, b'\\')
            elif ch == b'+':
                follow(y, x - 1, b'-')
                follow(y, x + 1, b'-')
                follow(y + 1, x - 1, b'/')
                follow(y + 1, x + 1, b'\\')
                follow(y + 1, x, b'|')
            elif ch == b'\\':
                follow(y + 1, x + 1, b'\\|o')
            elif ch == b'/':
                follow(y + 1, x - 1, b'/|o')
            elif ch == b'-':
                follow(y, x - 1, b'-+o')
                follow(y, x + 1, b'-+o')
        return result

    for y, line in enumerate(lines):
        for x, ch in enumerate(pycompat.bytestr(line)):
            if ch == b'#':  # comment
                break
            if _isname(ch):
                edges[getname(y, x)] += parents(y, x)

    return dict(edges)


class simplefilectx(object):
    def __init__(self, path, data):
        self._data = data
        self._path = path

    def data(self):
        return self._data

    def filenode(self):
        return None

    def path(self):
        return self._path

    def copysource(self):
        return None

    def flags(self):
        return b''


class simplecommitctx(context.committablectx):
    def __init__(self, repo, name, parentctxs, added):
        opts = {
            'changes': scmutil.status([], list(added), [], [], [], [], []),
            'date': b'0 0',
            'extra': {b'branch': b'default'},
        }
        super(simplecommitctx, self).__init__(repo, name, **opts)
        self._added = added
        self._parents = parentctxs
        while len(self._parents) < 2:
            self._parents.append(repo[nullid])

    def filectx(self, key):
        return simplefilectx(key, self._added[key])

    def commit(self):
        return self._repo.commitctx(self)

    def p1copies(self):
        return {}

    def p2copies(self):
        return {}


def _walkgraph(edges):
    """yield node, parents in topologically order"""
    visible = set(edges.keys())
    remaining = {}  # {str: [str]}
    for k, vs in edges.items():
        for v in vs:
            if v not in remaining:
                remaining[v] = []
        remaining[k] = vs[:]
    while remaining:
        leafs = [k for k, v in remaining.items() if not v]
        if not leafs:
            raise error.Abort(_('the graph has cycles'))
        for leaf in sorted(leafs):
            if leaf in visible:
                yield leaf, edges[leaf]
            del remaining[leaf]
            for k, v in remaining.items():
                if leaf in v:
                    v.remove(leaf)


def _getcomments(text):
    r"""
    >>> [pycompat.sysstr(s) for s in _getcomments(br'''
    ...        G
    ...        |
    ...  I D C F   # split: B -> E, F, G
    ...   \ \| |   # replace: C -> D -> H
    ...    H B E   # prune: F, I
    ...     \|/
    ...      A
    ... ''')]
    ['split: B -> E, F, G', 'replace: C -> D -> H', 'prune: F, I']
    """
    for line in text.splitlines():
        if b' # ' not in line:
            continue
        yield line.split(b' # ', 1)[1].split(b' # ')[0].strip()


@command(b'debugdrawdag', [])
def debugdrawdag(ui, repo, **opts):
    r"""read an ASCII graph from stdin and create changesets

    The ASCII graph is like what :hg:`log -G` outputs, with each `o` replaced
    to the name of the node. The command will create dummy changesets and local
    tags with those names to make the dummy changesets easier to be referred
    to.

    If the name of a node is a single character 'o', It will be replaced by the
    word to the right. This makes it easier to reuse
    :hg:`log -G -T '{desc}'` outputs.

    For root (no parents) nodes, revset can be used to query existing repo.
    Note that the revset cannot have confusing characters which can be seen as
    the part of the graph edges, like `|/+-\`.
    """
    text = ui.fin.read()

    # parse the graph and make sure len(parents) <= 2 for each node
    edges = _parseasciigraph(text)
    for k, v in edges.items():
        if len(v) > 2:
            raise error.Abort(_('%s: too many parents: %s') % (k, b' '.join(v)))

    # parse comments to get extra file content instructions
    files = collections.defaultdict(dict)  # {(name, path): content}
    comments = list(_getcomments(text))
    filere = re.compile(br'^(\w+)/([\w/]+)\s*=\s*(.*)$', re.M)
    for name, path, content in filere.findall(b'\n'.join(comments)):
        content = content.replace(br'\n', b'\n').replace(br'\1', b'\1')
        files[name][path] = content

    committed = {None: nullid}  # {name: node}

    # for leaf nodes, try to find existing nodes in repo
    for name, parents in edges.items():
        if len(parents) == 0:
            try:
                committed[name] = scmutil.revsingle(repo, name)
            except error.RepoLookupError:
                pass

    # commit in topological order
    for name, parents in _walkgraph(edges):
        if name in committed:
            continue
        pctxs = [repo[committed[n]] for n in parents]
        pctxs.sort(key=lambda c: c.node())
        added = {}
        if len(parents) > 1:
            # If it's a merge, take the files and contents from the parents
            for f in pctxs[1].manifest():
                if f not in pctxs[0].manifest():
                    added[f] = pctxs[1][f].data()
        else:
            # If it's not a merge, add a single file
            added[name] = name
        # add extra file contents in comments
        for path, content in files.get(name, {}).items():
            added[path] = content
        ctx = simplecommitctx(repo, name, pctxs, added)
        n = ctx.commit()
        committed[name] = n
        tagsmod.tag(
            repo, [name], n, message=None, user=None, date=None, local=True
        )

    # handle special comments
    with repo.wlock(), repo.lock(), repo.transaction(b'drawdag'):
        getctx = lambda x: repo.unfiltered()[committed[x.strip()]]
        for comment in comments:
            rels = []  # obsolete relationships
            args = comment.split(b':', 1)
            if len(args) <= 1:
                continue

            cmd = args[0].strip()
            arg = args[1].strip()

            if cmd in (b'replace', b'rebase', b'amend'):
                nodes = [getctx(m) for m in arg.split(b'->')]
                for i in range(len(nodes) - 1):
                    rels.append(((nodes[i],), (nodes[i + 1],)))
            elif cmd in (b'split',):
                pre, succs = arg.split(b'->')
                succs = succs.split(b',')
                rels.append(((getctx(pre),), (getctx(s) for s in succs)))
            elif cmd in (b'prune',):
                for n in arg.split(b','):
                    rels.append(((getctx(n),), ()))
            if rels:
                obsolete.createmarkers(repo, rels, date=(0, 0), operation=cmd)