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.

     1

#!/usr/bin/env python3

     2

#

     3

# mercurial - scalable distributed SCM

     4

#

     5

# Copyright 2005-2007 Olivia Mackall <olivia@selenic.com>

     6

#

     7

# This software may be used and distributed according to the terms of the

     8

# GNU General Public License version 2 or any later version.

     9

from __future__ import absolute_import

    10

    11

import os

    12

import sys

    13

    14

libdir = '@LIBDIR@'

    15

    16

if libdir != '@' 'LIBDIR' '@':

    17

    if not os.path.isabs(libdir):

    18

        libdir = os.path.join(

    19

            os.path.dirname(os.path.realpath(__file__)), libdir

    20

        )

    21

        libdir = os.path.abspath(libdir)

    22

    sys.path.insert(0, libdir)

    23

    24

# Make `pip install --user ...` packages available to the official Windows

    25

# build.  Most py2 packaging installs directly into the system python

    26

# environment, so no changes are necessary for other platforms.  The Windows

    27

# py2 package uses py2exe, which lacks a `site` module.  Hardcode it according

    28

# to the documentation.

    29

if getattr(sys, 'frozen', None) == 'console_exe':

    30

    vi = sys.version_info

    31

    sys.path.append(

    32

        os.path.join(

    33

            os.environ['APPDATA'],

    34

            'Python',

    35

            'Python%d%d' % (vi[0], vi[1]),

    36

            'site-packages',

    37

        )

    38

    )

    39

    40

from hgdemandimport import tracing

    41

    42

with tracing.log('hg script'):

    43

    # enable importing on demand to reduce startup time

    44

    try:

    45

        if sys.version_info[0] < 3 or sys.version_info >= (3, 6):

    46

            import hgdemandimport

    47

    48

            hgdemandimport.enable()

    49

    except ImportError:

    50

        sys.stderr.write(

    51

            "abort: couldn't find mercurial libraries in [%s]\n"

    52

            % ' '.join(sys.path)

    53

        )

    54

        sys.stderr.write("(check your install and PYTHONPATH)\n")

    55

        sys.exit(-1)

    56

    57

    from mercurial import dispatch

    58

    59

    dispatch.run()