view mercurial/node.py @ 50316:87f0155d68aa stable

revlog: improve the robustness of the splitting process

The previous "in-place" splitting, preserving the splitting on transaction
failure had a couple of issue in case of transaction rollback:
- a race windows that could still lead to a crash and data loss
- it corrupted the `fncache`.

So instead, we use a new approach that we summarized as "we do a backup of the
inline revlog pre-split, and we restore this in case of failure".
To make readers live easier, we don't overwrite the inline index file until
transaction finalization. (once the transaction get into its finalization phase,
it is not expected to rollback, unless some crash happens).

To do so, we write the index of the split index in a temporary file that we use
until transaction finalization. We also keep a backup of the initial inline file
to be able to rollback the split if needed.

As a result, transaction rollback cancel the split and no longer corrupt
fncache. We also no longer have a small inconsistency windows where the
transaction could be unrecoverable.

# node.py - basic nodeid manipulation for mercurial
#
# Copyright 2005, 2006 Olivia Mackall <[e-mail]>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.


import binascii

# This ugly style has a noticeable effect in manifest parsing
hex = binascii.hexlify
bin = binascii.unhexlify


def short(node):
    return hex(node[:6])


nullrev = -1

# pseudo identifier for working directory
# (experimental, so don't add too many dependencies on it)
wdirrev = 0x7FFFFFFF


class sha1nodeconstants:
    nodelen = 20

    # In hex, this is '0000000000000000000000000000000000000000'
    nullid = b"\0" * nodelen
    nullhex = hex(nullid)

    # Phony node value to stand-in for new files in some uses of
    # manifests.
    # In hex, this is '2121212121212121212121212121212121212121'
    newnodeid = b'!!!!!!!!!!!!!!!!!!!!'
    # In hex, this is '3030303030303030303030303030306164646564'
    addednodeid = b'000000000000000added'
    # In hex, this is '3030303030303030303030306d6f646966696564'
    modifiednodeid = b'000000000000modified'

    wdirfilenodeids = {newnodeid, addednodeid, modifiednodeid}

    # pseudo identifier for working directory
    # (experimental, so don't add too many dependencies on it)
    # In hex, this is 'ffffffffffffffffffffffffffffffffffffffff'
    wdirid = b"\xff" * nodelen
    wdirhex = hex(wdirid)


# legacy starting point for porting modules
nullid = sha1nodeconstants.nullid
nullhex = sha1nodeconstants.nullhex
newnodeid = sha1nodeconstants.newnodeid
addednodeid = sha1nodeconstants.addednodeid
modifiednodeid = sha1nodeconstants.modifiednodeid
wdirfilenodeids = sha1nodeconstants.wdirfilenodeids
wdirid = sha1nodeconstants.wdirid
wdirhex = sha1nodeconstants.wdirhex