Mercurial > hg
view mercurial/pure/parsers.py @ 26375:3686fa2b8eee
windows: insert file positioning call between reads and writes
fopen() and fdopen() have a unique-to-Windows requirement that
transitions between read and write operations in files opened
in modes r+, w+, and a+ perform a file positioning call
(fsetpos, fseek, or rewind) in between. While the MSDN docs don't
say what will happen if this is not done, observations reveal
that Python raises an IOError with errno 0. Furthermore, I
/think/ this behavior isn't deterministic. But I can reproduce
it reliably with subsequent patches applied that open revlogs
in a+ mode and perform both reads and writes.
This patch introduces a proxy class for file handles opened
in r+, w+, and a+ mode on Windows. The class intercepts calls
and audits whether a file positioning function has been called
between read and write operations. If not, a dummy, no-op seek
to the current file position is performed. This appears to be
sufficient to "trick" Windows into allowing transitions between
read and writes without raising errors.
author | Gregory Szorc <gregory.szorc@gmail.com> |
---|---|
date | Sun, 27 Sep 2015 18:46:53 -0700 |
parents | 4ece2847cf4c |
children | 6ab8c6511a6a |
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# parsers.py - Python implementation of parsers.c # # 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 mercurial.node import nullid import struct, zlib, cStringIO _pack = struct.pack _unpack = struct.unpack _compress = zlib.compress _decompress = zlib.decompress # Some code below makes tuples directly because it's more convenient. However, # code outside this module should always use dirstatetuple. def dirstatetuple(*x): # x is a tuple return x def parse_index2(data, inline): def gettype(q): return int(q & 0xFFFF) def offset_type(offset, type): return long(long(offset) << 16 | type) indexformatng = ">Qiiiiii20s12x" s = struct.calcsize(indexformatng) index = [] cache = None off = 0 l = len(data) - s append = index.append if inline: cache = (0, data) while off <= l: e = _unpack(indexformatng, data[off:off + s]) append(e) if e[1] < 0: break off += e[1] + s else: while off <= l: e = _unpack(indexformatng, data[off:off + s]) append(e) off += s if off != len(data): raise ValueError('corrupt index file') if index: e = list(index[0]) type = gettype(e[0]) e[0] = offset_type(0, type) index[0] = tuple(e) # add the magic null revision at -1 index.append((0, 0, 0, -1, -1, -1, -1, nullid)) return index, cache def parse_dirstate(dmap, copymap, st): parents = [st[:20], st[20: 40]] # dereference fields so they will be local in loop format = ">cllll" e_size = struct.calcsize(format) pos1 = 40 l = len(st) # the inner loop while pos1 < l: pos2 = pos1 + e_size e = _unpack(">cllll", st[pos1:pos2]) # a literal here is faster pos1 = pos2 + e[4] f = st[pos2:pos1] if '\0' in f: f, c = f.split('\0') copymap[f] = c dmap[f] = e[:4] return parents def pack_dirstate(dmap, copymap, pl, now): now = int(now) cs = cStringIO.StringIO() write = cs.write write("".join(pl)) for f, e in dmap.iteritems(): if e[0] == 'n' and e[3] == now: # The file was last modified "simultaneously" with the current # write to dirstate (i.e. within the same second for file- # systems with a granularity of 1 sec). This commonly happens # for at least a couple of files on 'update'. # The user could change the file without changing its size # within the same second. Invalidate the file's mtime in # dirstate, forcing future 'status' calls to compare the # contents of the file if the size is the same. This prevents # mistakenly treating such files as clean. e = dirstatetuple(e[0], e[1], e[2], -1) dmap[f] = e if f in copymap: f = "%s\0%s" % (f, copymap[f]) e = _pack(">cllll", e[0], e[1], e[2], e[3], len(f)) write(e) write(f) return cs.getvalue()