revlog: automatically read from opened file handles
The revlog reading code commonly opens a new file handle for
reading on demand. There is support for passing a file handle
to revlog.revision(). But it is marked as an internal argument.
When revlogs are written, we write() data as it is available. But
we don't flush() data until all revisions are written.
Putting these two traits together, it is possible for an in-process
revlog reader during active writes to trigger the opening of a new
file handle on a file with unflushed writes. The reader won't have
access to all "available" revlog data (as it hasn't been flushed).
And with the introduction of the previous patch, this can lead to
the revlog raising an error due to a partial read.
I witnessed this behavior when applying changegroup data (via
`hg pull`) before issue6006 was fixed via different means. Having
this and the previous patch in play would have helped cause errors
earlier rather than manifesting as hash verification failures.
While this has been a long-standing issue, I believe the relatively
new delta computation code has tickled it into being more common.
This is because the new delta computation code will compute deltas
in more scenarios. This can lead to revlog reading. While the delta
computation code is probably supposed to reuse file handles, it
appears it isn't doing so in all circumstances.
But the issue runs deeper than that. Theoretically, any code can
access revision data during revlog writes. It appears we were just
getting lucky that it wasn't. (The "add revision callback" passed to
addgroup() provides an avenue to do this.)
If I changed the revlog's behavior to not cache the full revision
text or to clear caches after revision insertion during addgroup(),
I was able to produce crashes 100% of the time when writing changelog
revisions. This is because changelog's add revision callback attempts
to resolve the revision data to access the changed files list. And
without the revision's fulltext being cached, we performed a revlog
read, which required opening a new file handle. This attempted to read
unflushed data, leading to a partial read and a crash.
This commit teaches the revlog to store the file handles used for
writing multiple revisions during addgroup(). It also teaches the
code for resolving a file handle when reading to use these handles,
if available. This ensures that *any* reads (regardless of their
source) use the active writing file handles, if available. These
file handles have access to the unflushed data because they wrote it.
This allows reads to complete without issue.
Differential Revision: https://phab.mercurial-scm.org/D5267
# config.py - configuration parsing for Mercurial
#
# Copyright 2009 Matt Mackall <mpm@selenic.com> and others
#
# 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 absolute_import
import errno
import os
from .i18n import _
from . import (
error,
pycompat,
util,
)
class config(object):
def __init__(self, data=None, includepaths=None):
self._data = {}
self._unset = []
self._includepaths = includepaths or []
if data:
for k in data._data:
self._data[k] = data[k].copy()
self._source = data._source.copy()
else:
self._source = util.cowdict()
def copy(self):
return config(self)
def __contains__(self, section):
return section in self._data
def hasitem(self, section, item):
return item in self._data.get(section, {})
def __getitem__(self, section):
return self._data.get(section, {})
def __iter__(self):
for d in self.sections():
yield d
def update(self, src):
self._source = self._source.preparewrite()
for s, n in src._unset:
ds = self._data.get(s, None)
if ds is not None and n in ds:
self._data[s] = ds.preparewrite()
del self._data[s][n]
del self._source[(s, n)]
for s in src:
ds = self._data.get(s, None)
if ds:
self._data[s] = ds.preparewrite()
else:
self._data[s] = util.cowsortdict()
self._data[s].update(src._data[s])
self._source.update(src._source)
def get(self, section, item, default=None):
return self._data.get(section, {}).get(item, default)
def backup(self, section, item):
"""return a tuple allowing restore to reinstall a previous value
The main reason we need it is because it handles the "no data" case.
"""
try:
value = self._data[section][item]
source = self.source(section, item)
return (section, item, value, source)
except KeyError:
return (section, item)
def source(self, section, item):
return self._source.get((section, item), "")
def sections(self):
return sorted(self._data.keys())
def items(self, section):
return list(self._data.get(section, {}).iteritems())
def set(self, section, item, value, source=""):
if pycompat.ispy3:
assert not isinstance(value, str), (
'config values may not be unicode strings on Python 3')
if section not in self:
self._data[section] = util.cowsortdict()
else:
self._data[section] = self._data[section].preparewrite()
self._data[section][item] = value
if source:
self._source = self._source.preparewrite()
self._source[(section, item)] = source
def restore(self, data):
"""restore data returned by self.backup"""
self._source = self._source.preparewrite()
if len(data) == 4:
# restore old data
section, item, value, source = data
self._data[section] = self._data[section].preparewrite()
self._data[section][item] = value
self._source[(section, item)] = source
else:
# no data before, remove everything
section, item = data
if section in self._data:
self._data[section].pop(item, None)
self._source.pop((section, item), None)
def parse(self, src, data, sections=None, remap=None, include=None):
sectionre = util.re.compile(br'\[([^\[]+)\]')
itemre = util.re.compile(br'([^=\s][^=]*?)\s*=\s*(.*\S|)')
contre = util.re.compile(br'\s+(\S|\S.*\S)\s*$')
emptyre = util.re.compile(br'(;|#|\s*$)')
commentre = util.re.compile(br'(;|#)')
unsetre = util.re.compile(br'%unset\s+(\S+)')
includere = util.re.compile(br'%include\s+(\S|\S.*\S)\s*$')
section = ""
item = None
line = 0
cont = False
if remap:
section = remap.get(section, section)
for l in data.splitlines(True):
line += 1
if line == 1 and l.startswith('\xef\xbb\xbf'):
# Someone set us up the BOM
l = l[3:]
if cont:
if commentre.match(l):
continue
m = contre.match(l)
if m:
if sections and section not in sections:
continue
v = self.get(section, item) + "\n" + m.group(1)
self.set(section, item, v, "%s:%d" % (src, line))
continue
item = None
cont = False
m = includere.match(l)
if m and include:
expanded = util.expandpath(m.group(1))
includepaths = [os.path.dirname(src)] + self._includepaths
for base in includepaths:
inc = os.path.normpath(os.path.join(base, expanded))
try:
include(inc, remap=remap, sections=sections)
break
except IOError as inst:
if inst.errno != errno.ENOENT:
raise error.ParseError(_("cannot include %s (%s)")
% (inc, inst.strerror),
"%s:%d" % (src, line))
continue
if emptyre.match(l):
continue
m = sectionre.match(l)
if m:
section = m.group(1)
if remap:
section = remap.get(section, section)
if section not in self:
self._data[section] = util.cowsortdict()
continue
m = itemre.match(l)
if m:
item = m.group(1)
cont = True
if sections and section not in sections:
continue
self.set(section, item, m.group(2), "%s:%d" % (src, line))
continue
m = unsetre.match(l)
if m:
name = m.group(1)
if sections and section not in sections:
continue
if self.get(section, name) is not None:
self._data[section] = self._data[section].preparewrite()
del self._data[section][name]
self._unset.append((section, name))
continue
raise error.ParseError(l.rstrip(), ("%s:%d" % (src, line)))
def read(self, path, fp=None, sections=None, remap=None):
if not fp:
fp = util.posixfile(path, 'rb')
assert getattr(fp, 'mode', r'rb') == r'rb', (
'config files must be opened in binary mode, got fp=%r mode=%r' % (
fp, fp.mode))
self.parse(path, fp.read(),
sections=sections, remap=remap, include=self.read)
def parselist(value):
"""parse a configuration value as a list of comma/space separated strings
>>> parselist(b'this,is "a small" ,test')
['this', 'is', 'a small', 'test']
"""
def _parse_plain(parts, s, offset):
whitespace = False
while offset < len(s) and (s[offset:offset + 1].isspace()
or s[offset:offset + 1] == ','):
whitespace = True
offset += 1
if offset >= len(s):
return None, parts, offset
if whitespace:
parts.append('')
if s[offset:offset + 1] == '"' and not parts[-1]:
return _parse_quote, parts, offset + 1
elif s[offset:offset + 1] == '"' and parts[-1][-1:] == '\\':
parts[-1] = parts[-1][:-1] + s[offset:offset + 1]
return _parse_plain, parts, offset + 1
parts[-1] += s[offset:offset + 1]
return _parse_plain, parts, offset + 1
def _parse_quote(parts, s, offset):
if offset < len(s) and s[offset:offset + 1] == '"': # ""
parts.append('')
offset += 1
while offset < len(s) and (s[offset:offset + 1].isspace() or
s[offset:offset + 1] == ','):
offset += 1
return _parse_plain, parts, offset
while offset < len(s) and s[offset:offset + 1] != '"':
if (s[offset:offset + 1] == '\\' and offset + 1 < len(s)
and s[offset + 1:offset + 2] == '"'):
offset += 1
parts[-1] += '"'
else:
parts[-1] += s[offset:offset + 1]
offset += 1
if offset >= len(s):
real_parts = _configlist(parts[-1])
if not real_parts:
parts[-1] = '"'
else:
real_parts[0] = '"' + real_parts[0]
parts = parts[:-1]
parts.extend(real_parts)
return None, parts, offset
offset += 1
while offset < len(s) and s[offset:offset + 1] in [' ', ',']:
offset += 1
if offset < len(s):
if offset + 1 == len(s) and s[offset:offset + 1] == '"':
parts[-1] += '"'
offset += 1
else:
parts.append('')
else:
return None, parts, offset
return _parse_plain, parts, offset
def _configlist(s):
s = s.rstrip(' ,')
if not s:
return []
parser, parts, offset = _parse_plain, [''], 0
while parser:
parser, parts, offset = parser(parts, s, offset)
return parts
if value is not None and isinstance(value, bytes):
result = _configlist(value.lstrip(' ,\n'))
else:
result = value
return result or []