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.

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[This file is here for historical purposes, all recent contributors

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should appear in the changelog directly]

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Andrea Arcangeli <andrea at suse.de>

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Thomas Arendsen Hein <thomas at intevation.de>

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Goffredo Baroncelli <kreijack at libero.it>

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Muli Ben-Yehuda <mulix at mulix.org>

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Mikael Berthe <mikael at lilotux.net>

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Benoit Boissinot <bboissin at gmail.com>

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Brendan Cully <brendan at kublai.com>

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Vincent Danjean <vdanjean.ml at free.fr>

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Jake Edge <jake at edge2.net>

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Michael Fetterman <michael.fetterman at intel.com>

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Edouard Gomez <ed.gomez at free.fr>

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Eric Hopper <hopper at omnifarious.org>

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Alecs King <alecsk at gmail.com>

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Volker Kleinfeld <Volker.Kleinfeld at gmx.de>

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Vadim Lebedev <vadim at mbdsys.com>

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Christopher Li <hg at chrisli.org>

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Chris Mason <mason at suse.com>

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Colin McMillen <mcmillen at cs.cmu.edu>

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Wojciech Milkowski <wmilkowski at interia.pl>

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Chad Netzer <chad.netzer at gmail.com>

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Bryan O'Sullivan <bos at serpentine.com>

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Vicent Seguí Pascual <vseguip at gmail.com>

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Sean Perry <shaleh at speakeasy.net>

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Nguyen Anh Quynh <aquynh at gmail.com>

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Ollivier Robert <roberto at keltia.freenix.fr>

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Alexander Schremmer <alex at alexanderweb.de>

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Arun Sharma <arun at sharma-home.net>

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Josef "Jeff" Sipek <jeffpc at optonline.net>

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Kevin Smith <yarcs at qualitycode.com>

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TK Soh <teekaysoh at yahoo.com>

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Radoslaw Szkodzinski <astralstorm at gorzow.mm.pl>

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Samuel Tardieu <sam at rfc1149.net>

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K Thananchayan <thananck at yahoo.com>

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Andrew Thompson <andrewkt at aktzero.com>

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Michael S. Tsirkin <mst at mellanox.co.il>

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Rafael Villar Burke <pachi at mmn-arquitectos.com>

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Tristan Wibberley <tristan at wibberley.org>

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Mark Williamson <mark.williamson at cl.cam.ac.uk>