# repocache.py - in-memory repository cache for long-running services

#

# Copyright 2018 Yuya Nishihara <yuya@tcha.org>

#

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

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

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)

    repo._phasecache.loadphaserevs(repo)

# 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._realopener = 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