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# rev_cache.py - caching branch information per revision
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#
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# This software may be used and distributed according to the terms of the
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# GNU General Public License version 2 or any later version.
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from __future__ import annotations
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import os
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import struct
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from ..node import (
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nullrev,
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)
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from .. import (
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encoding,
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error,
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util,
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)
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from ..utils import (
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stringutil,
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)
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calcsize = struct.calcsize
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pack_into = struct.pack_into
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unpack_from = struct.unpack_from
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# Revision branch info cache
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# The "V2" version use the same format as the "V1" but garantee it won't be
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# truncated, preventing SIGBUS when it is mmap-ed
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_rbcversion = b'-v2'
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_rbcnames = b'rbc-names' + _rbcversion
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_rbcrevs = b'rbc-revs' + _rbcversion
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_rbc_legacy_version = b'-v1'
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_rbc_legacy_names = b'rbc-names' + _rbc_legacy_version
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_rbc_legacy_revs = b'rbc-revs' + _rbc_legacy_version
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# [4 byte hash prefix][4 byte branch name number with sign bit indicating open]
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_rbcrecfmt = b'>4sI'
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_rbcrecsize = calcsize(_rbcrecfmt)
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_rbcmininc = 64 * _rbcrecsize
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_rbcnodelen = 4
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_rbcbranchidxmask = 0x7FFFFFFF
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_rbccloseflag = 0x80000000
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# with atomic replacement.
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REWRITE_RATIO = 0.2
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class rbcrevs:
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"""a byte string consisting of an immutable prefix followed by a mutable suffix"""
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def __init__(self, revs):
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self._prefix = revs
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self._rest = bytearray()
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def __len__(self):
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return len(self._prefix) + len(self._rest)
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def unpack_record(self, rbcrevidx):
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if rbcrevidx < len(self._prefix):
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return unpack_from(_rbcrecfmt, util.buffer(self._prefix), rbcrevidx)
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else:
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return unpack_from(
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_rbcrecfmt,
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util.buffer(self._rest),
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rbcrevidx - len(self._prefix),
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)
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def make_mutable(self):
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if len(self._prefix) > 0:
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entirety = bytearray()
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entirety[:] = self._prefix
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entirety.extend(self._rest)
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self._rest = entirety
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self._prefix = bytearray()
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def truncate(self, pos):
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self.make_mutable()
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del self._rest[pos:]
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def pack_into(self, rbcrevidx, node, branchidx):
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if rbcrevidx < len(self._prefix):
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self.make_mutable()
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buf = self._rest
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start_offset = rbcrevidx - len(self._prefix)
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end_offset = start_offset + _rbcrecsize
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if len(self._rest) < end_offset:
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# bytearray doesn't allocate extra space at least in Python 3.7.
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# When multiple changesets are added in a row, precise resize would
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# result in quadratic complexity. Overallocate to compensate by
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# using the classic doubling technique for dynamic arrays instead.
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# If there was a gap in the map before, less space will be reserved.
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self._rest.extend(b'\0' * end_offset)
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return pack_into(
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_rbcrecfmt,
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buf,
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start_offset,
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node,
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branchidx,
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)
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def extend(self, extension):
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return self._rest.extend(extension)
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def slice(self, begin, end):
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if begin < len(self._prefix):
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acc = bytearray()
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acc[:] = self._prefix[begin:end]
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acc.extend(
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self._rest[begin - len(self._prefix) : end - len(self._prefix)]
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)
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return acc
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return self._rest[begin - len(self._prefix) : end - len(self._prefix)]
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class revbranchcache:
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"""Persistent cache, mapping from revision number to branch name and close.
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This is a low level cache, independent of filtering.
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Branch names are stored in rbc-names in internal encoding separated by 0.
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rbc-names is append-only, and each branch name is only stored once and will
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thus have a unique index.
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The branch info for each revision is stored in rbc-revs as constant size
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records. The whole file is read into memory, but it is only 'parsed' on
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demand. The file is usually append-only but will be truncated if repo
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modification is detected.
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The record for each revision contains the first 4 bytes of the
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corresponding node hash, and the record is only used if it still matches.
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Even a completely trashed rbc-revs fill thus still give the right result
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while converging towards full recovery ... assuming no incorrectly matching
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node hashes.
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The record also contains 4 bytes where 31 bits contains the index of the
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branch and the last bit indicate that it is a branch close commit.
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The usage pattern for rbc-revs is thus somewhat similar to 00changelog.i
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and will grow with it but be 1/8th of its size.
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"""
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def __init__(self, repo, readonly=True):
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assert repo.filtername is None
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self._repo = repo
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self._names = [] # branch names in local encoding with static index
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self._rbcrevs = rbcrevs(bytearray())
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self._rbcsnameslen = 0 # length of names read at _rbcsnameslen
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v1_fallback = False
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try:
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try:
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bndata = repo.cachevfs.read(_rbcnames)
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except (IOError, OSError):
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# If we don't have "v2" data, we might have "v1" data worth
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# using.
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#
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# consider stop doing this many version after hg-6.9 release
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bndata = repo.cachevfs.read(_rbc_legacy_names)
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v1_fallback = True
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self._rbcsnameslen = len(bndata) # for verification before writing
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if bndata:
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self._names = [
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encoding.tolocal(bn) for bn in bndata.split(b'\0')
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]
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except (IOError, OSError):
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if readonly:
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# don't try to use cache - fall back to the slow path
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self.branchinfo = self._branchinfo
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if self._names:
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try:
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usemmap = repo.ui.configbool(b'storage', b'revbranchcache.mmap')
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if not v1_fallback:
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with repo.cachevfs(_rbcrevs) as fp:
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if usemmap and repo.cachevfs.is_mmap_safe(_rbcrevs):
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data = util.buffer(util.mmapread(fp))
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else:
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data = fp.read()
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else:
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# If we don't have "v2" data, we might have "v1" data worth
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# using.
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#
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# Consider stop doing this many version after hg-6.9
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# release.
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with repo.cachevfs(_rbc_legacy_revs) as fp:
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data = fp.read()
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self._rbcrevs = rbcrevs(data)
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except (IOError, OSError) as inst:
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repo.ui.debug(
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b"couldn't read revision branch cache: %s\n"
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% stringutil.forcebytestr(inst)
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)
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# remember number of good records on disk
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self._rbcrevslen = min(
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len(self._rbcrevs) // _rbcrecsize, len(repo.changelog)
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)
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if self._rbcrevslen == 0:
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self._names = []
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self._rbcnamescount = len(self._names) # number of names read at
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# _rbcsnameslen
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self._force_overwrite = False
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def _clear(self):
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self._rbcsnameslen = 0
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del self._names[:]
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self._rbcnamescount = 0
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self._rbcrevslen = len(self._repo.changelog)
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self._rbcrevs = rbcrevs(bytearray(self._rbcrevslen * _rbcrecsize))
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util.clearcachedproperty(self, b'_namesreverse')
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self._force_overwrite = True
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def invalidate(self, rev=0):
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self._rbcrevslen = rev
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self._rbcrevs.truncate(rev)
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self._force_overwrite = True
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@util.propertycache
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def _namesreverse(self):
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return {b: r for r, b in enumerate(self._names)}
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def branchinfo(self, rev):
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"""Return branch name and close flag for rev, using and updating
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persistent cache."""
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changelog = self._repo.changelog
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rbcrevidx = rev * _rbcrecsize
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# avoid negative index, changelog.read(nullrev) is fast without cache
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if rev == nullrev:
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return changelog.branchinfo(rev)
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# if requested rev isn't allocated, grow and cache the rev info
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if len(self._rbcrevs) < rbcrevidx + _rbcrecsize:
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return self._branchinfo(rev)
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# fast path: extract data from cache, use it if node is matching
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reponode = changelog.node(rev)[:_rbcnodelen]
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cachenode, branchidx = self._rbcrevs.unpack_record(rbcrevidx)
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close = bool(branchidx & _rbccloseflag)
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if close:
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branchidx &= _rbcbranchidxmask
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if cachenode == b'\0\0\0\0':
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pass
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elif cachenode == reponode:
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try:
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return self._names[branchidx], close
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except IndexError:
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# recover from invalid reference to unknown branch
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self._repo.ui.debug(
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b"referenced branch names not found"
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b" - rebuilding revision branch cache from scratch\n"
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)
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self._clear()
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else:
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# rev/node map has changed, invalidate the cache from here up
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self._repo.ui.debug(
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b"history modification detected - truncating "
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b"revision branch cache to revision %d\n" % rev
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)
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truncate = rbcrevidx + _rbcrecsize
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self._rbcrevs.truncate(truncate)
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self._rbcrevslen = min(self._rbcrevslen, truncate)
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# fall back to slow path and make sure it will be written to disk
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return self._branchinfo(rev)
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def _branchinfo(self, rev):
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"""Retrieve branch info from changelog and update _rbcrevs"""
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changelog = self._repo.changelog
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b, close = changelog.branchinfo(rev)
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if b in self._namesreverse:
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branchidx = self._namesreverse[b]
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else:
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branchidx = len(self._names)
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self._names.append(b)
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self._namesreverse[b] = branchidx
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reponode = changelog.node(rev)
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if close:
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branchidx |= _rbccloseflag
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self._setcachedata(rev, reponode, branchidx)
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return b, close
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def setdata(self, rev, changelogrevision):
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"""add new data information to the cache"""
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branch, close = changelogrevision.branchinfo
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if branch in self._namesreverse:
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branchidx = self._namesreverse[branch]
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else:
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branchidx = len(self._names)
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self._names.append(branch)
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self._namesreverse[branch] = branchidx
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if close:
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branchidx |= _rbccloseflag
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self._setcachedata(rev, self._repo.changelog.node(rev), branchidx)
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# If no cache data were readable (non exists, bad permission, etc)
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# the cache was bypassing itself by setting:
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#
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# self.branchinfo = self._branchinfo
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#
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# Since we now have data in the cache, we need to drop this bypassing.
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if 'branchinfo' in vars(self):
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del self.branchinfo
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def _setcachedata(self, rev, node, branchidx):
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"""Writes the node's branch data to the in-memory cache data."""
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if rev == nullrev:
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return
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rbcrevidx = rev * _rbcrecsize
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self._rbcrevs.pack_into(rbcrevidx, node, branchidx)
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self._rbcrevslen = min(self._rbcrevslen, rev)
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tr = self._repo.currenttransaction()
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if tr:
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tr.addfinalize(b'write-revbranchcache', self.write)
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def write(self, tr=None):
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"""Save branch cache if it is dirty."""
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repo = self._repo
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wlock = None
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step = b''
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try:
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# write the new names
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if self._rbcnamescount < len(self._names):
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wlock = repo.wlock(wait=False)
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step = b' names'
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self._writenames(repo)
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# write the new revs
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start = self._rbcrevslen * _rbcrecsize
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if self._force_overwrite or start != len(self._rbcrevs):
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step = b''
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if wlock is None:
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wlock = repo.wlock(wait=False)
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self._writerevs(repo, start)
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except (IOError, OSError, error.Abort, error.LockError) as inst:
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repo.ui.debug(
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b"couldn't write revision branch cache%s: %s\n"
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% (step, stringutil.forcebytestr(inst))
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)
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finally:
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if wlock is not None:
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wlock.release()
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def _writenames(self, repo):
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"""write the new branch names to revbranchcache"""
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f = None
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try:
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if self._rbcnamescount != 0:
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f = repo.cachevfs.open(_rbcnames, b'ab')
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if f.tell() == self._rbcsnameslen:
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f.write(b'\0')
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else:
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f.close()
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f = None
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repo.ui.debug(b"%s changed - rewriting it\n" % _rbcnames)
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self._rbcnamescount = 0
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self._rbcrevslen = 0
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if self._rbcnamescount == 0:
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# before rewriting names, make sure references are removed
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repo.cachevfs.unlinkpath(_rbcrevs, ignoremissing=True)
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f = repo.cachevfs.open(_rbcnames, b'wb')
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names = self._names[self._rbcnamescount :]
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from_local = encoding.fromlocal
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data = b'\0'.join(from_local(b) for b in names)
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f.write(data)
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self._rbcsnameslen = f.tell()
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finally:
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if f is not None:
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f.close()
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self._rbcnamescount = len(self._names)
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def _writerevs(self, repo, start):
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"""write the new revs to revbranchcache"""
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revs = min(len(repo.changelog), len(self._rbcrevs) // _rbcrecsize)
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end = revs * _rbcrecsize
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if self._force_overwrite:
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start = 0
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with repo.cachevfs.open(_rbcrevs, b'a+b') as f:
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pass # this make sure the file exist…
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with repo.cachevfs.open(_rbcrevs, b'r+b') as f:
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f.seek(0, os.SEEK_END)
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current_size = f.tell()
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if current_size < start:
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start = 0
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if current_size != start:
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threshold = current_size * REWRITE_RATIO
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if (max(end, current_size) - start) < threshold:
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# end affected, let overwrite the bad value
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dbg = b"overwriting %d bytes from %d in cache/%s"
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dbg %= (current_size - start, start, _rbcrevs)
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if end < current_size:
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extra = b" leaving (%d trailing bytes)"
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extra %= current_size - end
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dbg += extra
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dbg += b'\n'
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repo.ui.debug(dbg)
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else:
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start = 0
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dbg = b"resetting content of cache/%s\n" % _rbcrevs
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repo.ui.debug(dbg)
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if start > 0:
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f.seek(start)
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f.write(self._rbcrevs.slice(start, end))
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else:
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f.close()
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with repo.cachevfs.open(
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_rbcrevs,
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b'wb',
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atomictemp=True,
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) as rev_file:
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rev_file.write(self._rbcrevs.slice(start, end))
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self._rbcrevslen = revs
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self._force_overwrite = False
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