rev-branch-cache: move the code in a dedicated module
The branchmap module is getting huge and the rev branch cache is fully
independent, lets move it elsewhere.
# rev_cache.py - caching branch information per revision
#
# 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 struct
from ..node import (
nullrev,
)
from .. import (
encoding,
error,
util,
)
from ..utils import (
stringutil,
)
calcsize = struct.calcsize
pack_into = struct.pack_into
unpack_from = struct.unpack_from
# Revision branch info cache
_rbcversion = b'-v1'
_rbcnames = b'rbc-names' + _rbcversion
_rbcrevs = b'rbc-revs' + _rbcversion
# [4 byte hash prefix][4 byte branch name number with sign bit indicating open]
_rbcrecfmt = b'>4sI'
_rbcrecsize = calcsize(_rbcrecfmt)
_rbcmininc = 64 * _rbcrecsize
_rbcnodelen = 4
_rbcbranchidxmask = 0x7FFFFFFF
_rbccloseflag = 0x80000000
class rbcrevs:
"""a byte string consisting of an immutable prefix followed by a mutable suffix"""
def __init__(self, revs):
self._prefix = revs
self._rest = bytearray()
def __len__(self):
return len(self._prefix) + len(self._rest)
def unpack_record(self, rbcrevidx):
if rbcrevidx < len(self._prefix):
return unpack_from(_rbcrecfmt, util.buffer(self._prefix), rbcrevidx)
else:
return unpack_from(
_rbcrecfmt,
util.buffer(self._rest),
rbcrevidx - len(self._prefix),
)
def make_mutable(self):
if len(self._prefix) > 0:
entirety = bytearray()
entirety[:] = self._prefix
entirety.extend(self._rest)
self._rest = entirety
self._prefix = bytearray()
def truncate(self, pos):
self.make_mutable()
del self._rest[pos:]
def pack_into(self, rbcrevidx, node, branchidx):
if rbcrevidx < len(self._prefix):
self.make_mutable()
buf = self._rest
start_offset = rbcrevidx - len(self._prefix)
end_offset = start_offset + _rbcrecsize
if len(self._rest) < end_offset:
# bytearray doesn't allocate extra space at least in Python 3.7.
# When multiple changesets are added in a row, precise resize would
# result in quadratic complexity. Overallocate to compensate by
# using the classic doubling technique for dynamic arrays instead.
# If there was a gap in the map before, less space will be reserved.
self._rest.extend(b'\0' * end_offset)
return pack_into(
_rbcrecfmt,
buf,
start_offset,
node,
branchidx,
)
def extend(self, extension):
return self._rest.extend(extension)
def slice(self, begin, end):
if begin < len(self._prefix):
acc = bytearray()
acc[:] = self._prefix[begin:end]
acc.extend(
self._rest[begin - len(self._prefix) : end - len(self._prefix)]
)
return acc
return self._rest[begin - len(self._prefix) : end - len(self._prefix)]
class revbranchcache:
"""Persistent cache, mapping from revision number to branch name and close.
This is a low level cache, independent of filtering.
Branch names are stored in rbc-names in internal encoding separated by 0.
rbc-names is append-only, and each branch name is only stored once and will
thus have a unique index.
The branch info for each revision is stored in rbc-revs as constant size
records. The whole file is read into memory, but it is only 'parsed' on
demand. The file is usually append-only but will be truncated if repo
modification is detected.
The record for each revision contains the first 4 bytes of the
corresponding node hash, and the record is only used if it still matches.
Even a completely trashed rbc-revs fill thus still give the right result
while converging towards full recovery ... assuming no incorrectly matching
node hashes.
The record also contains 4 bytes where 31 bits contains the index of the
branch and the last bit indicate that it is a branch close commit.
The usage pattern for rbc-revs is thus somewhat similar to 00changelog.i
and will grow with it but be 1/8th of its size.
"""
def __init__(self, repo, readonly=True):
assert repo.filtername is None
self._repo = repo
self._names = [] # branch names in local encoding with static index
self._rbcrevs = rbcrevs(bytearray())
self._rbcsnameslen = 0 # length of names read at _rbcsnameslen
try:
bndata = repo.cachevfs.read(_rbcnames)
self._rbcsnameslen = len(bndata) # for verification before writing
if bndata:
self._names = [
encoding.tolocal(bn) for bn in bndata.split(b'\0')
]
except (IOError, OSError):
if readonly:
# don't try to use cache - fall back to the slow path
self.branchinfo = self._branchinfo
if self._names:
try:
usemmap = repo.ui.configbool(b'storage', b'revbranchcache.mmap')
with repo.cachevfs(_rbcrevs) as fp:
if usemmap and repo.cachevfs.is_mmap_safe(_rbcrevs):
data = util.buffer(util.mmapread(fp))
else:
data = fp.read()
self._rbcrevs = rbcrevs(data)
except (IOError, OSError) as inst:
repo.ui.debug(
b"couldn't read revision branch cache: %s\n"
% stringutil.forcebytestr(inst)
)
# remember number of good records on disk
self._rbcrevslen = min(
len(self._rbcrevs) // _rbcrecsize, len(repo.changelog)
)
if self._rbcrevslen == 0:
self._names = []
self._rbcnamescount = len(self._names) # number of names read at
# _rbcsnameslen
def _clear(self):
self._rbcsnameslen = 0
del self._names[:]
self._rbcnamescount = 0
self._rbcrevslen = len(self._repo.changelog)
self._rbcrevs = rbcrevs(bytearray(self._rbcrevslen * _rbcrecsize))
util.clearcachedproperty(self, b'_namesreverse')
@util.propertycache
def _namesreverse(self):
return {b: r for r, b in enumerate(self._names)}
def branchinfo(self, rev):
"""Return branch name and close flag for rev, using and updating
persistent cache."""
changelog = self._repo.changelog
rbcrevidx = rev * _rbcrecsize
# avoid negative index, changelog.read(nullrev) is fast without cache
if rev == nullrev:
return changelog.branchinfo(rev)
# if requested rev isn't allocated, grow and cache the rev info
if len(self._rbcrevs) < rbcrevidx + _rbcrecsize:
return self._branchinfo(rev)
# fast path: extract data from cache, use it if node is matching
reponode = changelog.node(rev)[:_rbcnodelen]
cachenode, branchidx = self._rbcrevs.unpack_record(rbcrevidx)
close = bool(branchidx & _rbccloseflag)
if close:
branchidx &= _rbcbranchidxmask
if cachenode == b'\0\0\0\0':
pass
elif cachenode == reponode:
try:
return self._names[branchidx], close
except IndexError:
# recover from invalid reference to unknown branch
self._repo.ui.debug(
b"referenced branch names not found"
b" - rebuilding revision branch cache from scratch\n"
)
self._clear()
else:
# rev/node map has changed, invalidate the cache from here up
self._repo.ui.debug(
b"history modification detected - truncating "
b"revision branch cache to revision %d\n" % rev
)
truncate = rbcrevidx + _rbcrecsize
self._rbcrevs.truncate(truncate)
self._rbcrevslen = min(self._rbcrevslen, truncate)
# fall back to slow path and make sure it will be written to disk
return self._branchinfo(rev)
def _branchinfo(self, rev):
"""Retrieve branch info from changelog and update _rbcrevs"""
changelog = self._repo.changelog
b, close = changelog.branchinfo(rev)
if b in self._namesreverse:
branchidx = self._namesreverse[b]
else:
branchidx = len(self._names)
self._names.append(b)
self._namesreverse[b] = branchidx
reponode = changelog.node(rev)
if close:
branchidx |= _rbccloseflag
self._setcachedata(rev, reponode, branchidx)
return b, close
def setdata(self, rev, changelogrevision):
"""add new data information to the cache"""
branch, close = changelogrevision.branchinfo
if branch in self._namesreverse:
branchidx = self._namesreverse[branch]
else:
branchidx = len(self._names)
self._names.append(branch)
self._namesreverse[branch] = branchidx
if close:
branchidx |= _rbccloseflag
self._setcachedata(rev, self._repo.changelog.node(rev), branchidx)
# If no cache data were readable (non exists, bad permission, etc)
# the cache was bypassing itself by setting:
#
# self.branchinfo = self._branchinfo
#
# Since we now have data in the cache, we need to drop this bypassing.
if 'branchinfo' in vars(self):
del self.branchinfo
def _setcachedata(self, rev, node, branchidx):
"""Writes the node's branch data to the in-memory cache data."""
if rev == nullrev:
return
rbcrevidx = rev * _rbcrecsize
self._rbcrevs.pack_into(rbcrevidx, node, branchidx)
self._rbcrevslen = min(self._rbcrevslen, rev)
tr = self._repo.currenttransaction()
if tr:
tr.addfinalize(b'write-revbranchcache', self.write)
def write(self, tr=None):
"""Save branch cache if it is dirty."""
repo = self._repo
wlock = None
step = b''
try:
# write the new names
if self._rbcnamescount < len(self._names):
wlock = repo.wlock(wait=False)
step = b' names'
self._writenames(repo)
# write the new revs
start = self._rbcrevslen * _rbcrecsize
if start != len(self._rbcrevs):
step = b''
if wlock is None:
wlock = repo.wlock(wait=False)
self._writerevs(repo, start)
except (IOError, OSError, error.Abort, error.LockError) as inst:
repo.ui.debug(
b"couldn't write revision branch cache%s: %s\n"
% (step, stringutil.forcebytestr(inst))
)
finally:
if wlock is not None:
wlock.release()
def _writenames(self, repo):
"""write the new branch names to revbranchcache"""
if self._rbcnamescount != 0:
f = repo.cachevfs.open(_rbcnames, b'ab')
if f.tell() == self._rbcsnameslen:
f.write(b'\0')
else:
f.close()
repo.ui.debug(b"%s changed - rewriting it\n" % _rbcnames)
self._rbcnamescount = 0
self._rbcrevslen = 0
if self._rbcnamescount == 0:
# before rewriting names, make sure references are removed
repo.cachevfs.unlinkpath(_rbcrevs, ignoremissing=True)
f = repo.cachevfs.open(_rbcnames, b'wb')
f.write(
b'\0'.join(
encoding.fromlocal(b)
for b in self._names[self._rbcnamescount :]
)
)
self._rbcsnameslen = f.tell()
f.close()
self._rbcnamescount = len(self._names)
def _writerevs(self, repo, start):
"""write the new revs to revbranchcache"""
revs = min(len(repo.changelog), len(self._rbcrevs) // _rbcrecsize)
with repo.cachevfs.open(_rbcrevs, b'ab') as f:
if f.tell() != start:
repo.ui.debug(
b"truncating cache/%s to %d\n" % (_rbcrevs, start)
)
f.seek(start)
if f.tell() != start:
start = 0
f.seek(start)
f.truncate()
end = revs * _rbcrecsize
f.write(self._rbcrevs.slice(start, end))
self._rbcrevslen = revs