view mercurial/repocache.py @ 52292:085cc409847d

sslutil: bump the default minimum TLS version of the client to 1.2 (BC)

TLS v1.0 and v1.1 are deprecated by RFC8996[1]:

   These versions lack support for current and recommended cryptographic
   algorithms and mechanisms, and various government and industry profiles of
   applications using TLS now mandate avoiding these old TLS versions.
   TLS version 1.2 became the recommended version for IETF protocols in
   2008 (subsequently being obsoleted by TLS version 1.3 in 2018)...

Various browsers have disabled or removed it[2][3][4], as have various internet
services, and Windows 11 has it disabled by default[5].  We should move on too.
(We should also bump it on the server side, as this config only affects clients
not allowing a server to negotiate down.  But the only server-side config is a
`devel` option to pick exactly one protocol version and is commented as a
footgun, so I'm hesitant to touch that.  See 7dec5e441bf7 for details, which
states that using `hg serve` directly isn't expected for a web service.)

I'm not knowledgeable enough in this area to know if we should follow up with
disabling certain ciphers too.  But this should provide better security on its
own.

[1] https://datatracker.ietf.org/doc/rfc8996/
[2] https://learn.microsoft.com/en-us/DeployEdge/microsoft-edge-policies#sslversionmin
[3] https://hacks.mozilla.org/2020/02/its-the-boot-for-tls-1-0-and-tls-1-1/
[4] https://security.googleblog.com/2018/10/modernizing-transport-security.html
[5] https://techcommunity.microsoft.com/blog/windows-itpro-blog/tls-1-0-and-tls-1-1-soon-to-be-disabled-in-windows/3887947

# repocache.py - in-memory repository cache for long-running services
#
# Copyright 2018 Yuya Nishihara <[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 annotations

import collections
import gc
import threading

from . import (
    error,
    hg,
    obsolete,
    scmutil,
    util,
)


class repoloader:
    """Load repositories in background thread

    This is designed for a forking server. A cached repo cannot be obtained
    until the server fork()s a worker and the loader thread stops.
    """

    def __init__(self, ui, maxlen):
        self._ui = ui.copy()
        self._cache = util.lrucachedict(max=maxlen)
        # use deque and Event instead of Queue since deque can discard
        # old items to keep at most maxlen items.
        self._inqueue = collections.deque(maxlen=maxlen)
        self._accepting = False
        self._newentry = threading.Event()
        self._thread = None

    def start(self):
        assert not self._thread
        if self._inqueue.maxlen == 0:
            # no need to spawn loader thread as the cache is disabled
            return
        self._accepting = True
        self._thread = threading.Thread(target=self._mainloop)
        self._thread.start()

    def stop(self):
        if not self._thread:
            return
        self._accepting = False
        self._newentry.set()
        self._thread.join()
        self._thread = None
        self._cache.clear()
        self._inqueue.clear()

    def load(self, path):
        """Request to load the specified repository in background"""
        self._inqueue.append(path)
        self._newentry.set()

    def get(self, path):
        """Return a cached repo if available

        This function must be called after fork(), where the loader thread
        is stopped. Otherwise, the returned repo might be updated by the
        loader thread.
        """
        if self._thread and self._thread.is_alive():
            raise error.ProgrammingError(
                b'cannot obtain cached repo while loader is active'
            )
        return self._cache.peek(path, None)

    def _mainloop(self):
        while self._accepting:
            # Avoid heavy GC after fork(), which would cancel the benefit of
            # COW. We assume that GIL is acquired while GC is underway in the
            # loader thread. If that isn't true, we might have to move
            # gc.collect() to the main thread so that fork() would never stop
            # the thread where GC is in progress.
            gc.collect()

            self._newentry.wait()
            while self._accepting:
                self._newentry.clear()
                try:
                    path = self._inqueue.popleft()
                except IndexError:
                    break
                scmutil.callcatch(self._ui, lambda: self._load(path))

    def _load(self, path):
        start = util.timer()
        # TODO: repo should be recreated if storage configuration changed
        try:
            # pop before loading so inconsistent state wouldn't be exposed
            repo = self._cache.pop(path)
        except KeyError:
            repo = hg.repository(self._ui, path).unfiltered()
        _warmupcache(repo)
        repo.ui.log(
            b'repocache',
            b'loaded repo into cache: %s (in %.3fs)\n',
            path,
            util.timer() - start,
        )
        self._cache.insert(path, repo)


# TODO: think about proper API of preloading cache
def _warmupcache(repo):
    repo.invalidateall()
    repo.changelog
    repo.obsstore._all
    repo.obsstore.successors
    repo.obsstore.predecessors
    repo.obsstore.children
    for name in obsolete.cachefuncs:
        obsolete.getrevs(repo, name)
    # ensure the phase cache is fully initialized
    repo._phasecache.phase(repo, repo.changelog.tiprev())


# TODO: think about proper API of attaching preloaded attributes
def copycache(srcrepo, destrepo):
    """Copy cached attributes from srcrepo to destrepo"""
    destfilecache = destrepo._filecache
    srcfilecache = srcrepo._filecache
    if b'changelog' in srcfilecache:
        destfilecache[b'changelog'] = ce = srcfilecache[b'changelog']
        ce.obj.opener = ce.obj._inner.opener = destrepo.svfs
    if b'obsstore' in srcfilecache:
        destfilecache[b'obsstore'] = ce = srcfilecache[b'obsstore']
        ce.obj.svfs = destrepo.svfs
    if b'_phasecache' in srcfilecache:
        destfilecache[b'_phasecache'] = ce = srcfilecache[b'_phasecache']
        ce.obj.opener = destrepo.svfs