nodemap: use an explicit "Block" object in the reference implementation

This will help us to introduce some test around the data currently written on
disk.

Differential Revision: https://phab.mercurial-scm.org/D7842

mercurial/revlogutils/nodemap.py

@@ -1,303 +1,309
 # nodemap.py - nodemap related code and utilities
 #
 # Copyright 2019 Pierre-Yves David <[e-mail]>
 # Copyright 2019 George Racinet <[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.
 
 from __future__ import absolute_import
 
 import os
 import re
 import struct
 
 from .. import (
     error,
     node as nodemod,
     util,
 )
 
 
 class NodeMap(dict):
     def __missing__(self, x):
         raise error.RevlogError(b'unknown node: %s' % x)
 
 
 def persisted_data(revlog):
     """read the nodemap for a revlog from disk"""
     if revlog.nodemap_file is None:
         return None
     pdata = revlog.opener.tryread(revlog.nodemap_file)
     if not pdata:
         return None
     offset = 0
     (version,) = S_VERSION.unpack(pdata[offset : offset + S_VERSION.size])
     if version != ONDISK_VERSION:
         return None
     offset += S_VERSION.size
     (uuid_size,) = S_HEADER.unpack(pdata[offset : offset + S_HEADER.size])
     offset += S_HEADER.size
     uid = pdata[offset : offset + uuid_size]
 
     filename = _rawdata_filepath(revlog, uid)
     return revlog.opener.tryread(filename)
 
 
 def setup_persistent_nodemap(tr, revlog):
     """Install whatever is needed transaction side to persist a nodemap on disk
 
     (only actually persist the nodemap if this is relevant for this revlog)
     """
     if revlog._inline:
         return  # inlined revlog are too small for this to be relevant
     if revlog.nodemap_file is None:
         return  # we do not use persistent_nodemap on this revlog
     callback_id = b"revlog-persistent-nodemap-%s" % revlog.nodemap_file
     if tr.hasfinalize(callback_id):
         return  # no need to register again
     tr.addfinalize(callback_id, lambda tr: _persist_nodemap(tr, revlog))
 
 
 def _persist_nodemap(tr, revlog):
     """Write nodemap data on disk for a given revlog
     """
     if getattr(revlog, 'filteredrevs', ()):
         raise error.ProgrammingError(
             "cannot persist nodemap of a filtered changelog"
         )
     if revlog.nodemap_file is None:
         msg = "calling persist nodemap on a revlog without the feature enableb"
         raise error.ProgrammingError(msg)
     if util.safehasattr(revlog.index, "nodemap_data_all"):
         data = revlog.index.nodemap_data_all()
     else:
         data = persistent_data(revlog.index)
     uid = _make_uid()
     datafile = _rawdata_filepath(revlog, uid)
     olds = _other_rawdata_filepath(revlog, uid)
     if olds:
         realvfs = getattr(revlog, '_realopener', revlog.opener)
 
         def cleanup(tr):
             for oldfile in olds:
                 realvfs.tryunlink(oldfile)
 
         callback_id = b"revlog-cleanup-nodemap-%s" % revlog.nodemap_file
         tr.addpostclose(callback_id, cleanup)
     # EXP-TODO: if this is a cache, this should use a cache vfs, not a
     # store vfs
     with revlog.opener(datafile, b'w') as fd:
         fd.write(data)
     # EXP-TODO: if this is a cache, this should use a cache vfs, not a
     # store vfs
     with revlog.opener(revlog.nodemap_file, b'w', atomictemp=True) as fp:
         fp.write(_serialize_docket(uid))
     # EXP-TODO: if the transaction abort, we should remove the new data and
     # reinstall the old one.
 
 
 ### Nodemap docket file
 #
 # The nodemap data are stored on disk using 2 files:
 #
 # * a raw data files containing a persistent nodemap
 #   (see `Nodemap Trie` section)
 #
 # * a small "docket" file containing medatadata
 #
 # While the nodemap data can be multiple tens of megabytes, the "docket" is
 # small, it is easy to update it automatically or to duplicated its content
 # during a transaction.
 #
 # Multiple raw data can exist at the same time (The currently valid one and a
 # new one beind used by an in progress transaction). To accomodate this, the
 # filename hosting the raw data has a variable parts. The exact filename is
 # specified inside the "docket" file.
 #
 # The docket file contains information to find, qualify and validate the raw
 # data. Its content is currently very light, but it will expand as the on disk
 # nodemap gains the necessary features to be used in production.
 
 # version 0 is experimental, no BC garantee, do no use outside of tests.
 ONDISK_VERSION = 0
 
 S_VERSION = struct.Struct(">B")
 S_HEADER = struct.Struct(">B")
 
 ID_SIZE = 8
 
 
 def _make_uid():
     """return a new unique identifier.
 
     The identifier is random and composed of ascii characters."""
     return nodemod.hex(os.urandom(ID_SIZE))
 
 
 def _serialize_docket(uid):
     """return serialized bytes for a docket using the passed uid"""
     data = []
     data.append(S_VERSION.pack(ONDISK_VERSION))
     data.append(S_HEADER.pack(len(uid)))
     data.append(uid)
     return b''.join(data)
 
 
 def _rawdata_filepath(revlog, uid):
     """The (vfs relative) nodemap's rawdata file for a given uid"""
     prefix = revlog.nodemap_file[:-2]
     return b"%s-%s.nd" % (prefix, uid)
 
 
 def _other_rawdata_filepath(revlog, uid):
     prefix = revlog.nodemap_file[:-2]
     pattern = re.compile(b"(^|/)%s-[0-9a-f]+\.nd$" % prefix)
     new_file_path = _rawdata_filepath(revlog, uid)
     new_file_name = revlog.opener.basename(new_file_path)
     dirpath = revlog.opener.dirname(new_file_path)
     others = []
     for f in revlog.opener.listdir(dirpath):
         if pattern.match(f) and f != new_file_name:
             others.append(f)
     return others
 
 
 ### Nodemap Trie
 #
 # This is a simple reference implementation to compute and persist a nodemap
 # trie. This reference implementation is write only. The python version of this
 # is not expected to be actually used, since it wont provide performance
 # improvement over existing non-persistent C implementation.
 #
 # The nodemap is persisted as Trie using 4bits-address/16-entries block. each
 # revision can be adressed using its node shortest prefix.
 #
 # The trie is stored as a sequence of block. Each block contains 16 entries
 # (signed 64bit integer, big endian). Each entry can be one of the following:
 #
 #  * value >=  0 -> index of sub-block
 #  * value == -1 -> no value
 #  * value <  -1 -> a revision value: rev = -(value+10)
 #
 # The implementation focus on simplicity, not on performance. A Rust
 # implementation should provide a efficient version of the same binary
 # persistence. This reference python implementation is never meant to be
 # extensively use in production.
 
 
 def persistent_data(index):
     """return the persistent binary form for a nodemap for a given index
     """
     trie = _build_trie(index)
     return _persist_trie(trie)
 
 
 S_BLOCK = struct.Struct(">" + ("l" * 16))
 
 NO_ENTRY = -1
 # rev 0 need to be -2 because 0 is used by block, -1 is a special value.
 REV_OFFSET = 2
 
 
 def _transform_rev(rev):
     """Return the number used to represent the rev in the tree.
 
     (or retrieve a rev number from such representation)
 
     Note that this is an involution, a function equal to its inverse (i.e.
     which gives the identity when applied to itself).
     """
     return -(rev + REV_OFFSET)
 
 
 def _to_int(hex_digit):
     """turn an hexadecimal digit into a proper integer"""
     return int(hex_digit, 16)
 
 
+class Block(dict):
+    """represent a block of the Trie
+
+    contains up to 16 entry indexed from 0 to 15"""
+
+
 def _build_trie(index):
     """build a nodemap trie
 
     The nodemap stores revision number for each unique prefix.
 
     Each block is a dictionary with keys in `[0, 15]`. Values are either
     another block or a revision number.
     """
-    root = {}
+    root = Block()
     for rev in range(len(index)):
         hex = nodemod.hex(index[rev][7])
         _insert_into_block(index, 0, root, rev, hex)
     return root
 
 
 def _insert_into_block(index, level, block, current_rev, current_hex):
     """insert a new revision in a block
 
     index: the index we are adding revision for
     level: the depth of the current block in the trie
     block: the block currently being considered
     current_rev: the revision number we are adding
     current_hex: the hexadecimal representation of the of that revision
     """
     hex_digit = _to_int(current_hex[level : level + 1])
     entry = block.get(hex_digit)
     if entry is None:
         # no entry, simply store the revision number
         block[hex_digit] = current_rev
     elif isinstance(entry, dict):
         # need to recurse to an underlying block
         _insert_into_block(index, level + 1, entry, current_rev, current_hex)
     else:
         # collision with a previously unique prefix, inserting new
         # vertices to fit both entry.
         other_hex = nodemod.hex(index[entry][7])
         other_rev = entry
-        new = {}
+        new = Block()
         block[hex_digit] = new
         _insert_into_block(index, level + 1, new, other_rev, other_hex)
         _insert_into_block(index, level + 1, new, current_rev, current_hex)
 
 
 def _persist_trie(root):
     """turn a nodemap trie into persistent binary data
 
     See `_build_trie` for nodemap trie structure"""
     block_map = {}
     chunks = []
     for tn in _walk_trie(root):
         block_map[id(tn)] = len(chunks)
         chunks.append(_persist_block(tn, block_map))
     return b''.join(chunks)
 
 
 def _walk_trie(block):
     """yield all the block in a trie
 
     Children blocks are always yield before their parent block.
     """
     for (_, item) in sorted(block.items()):
         if isinstance(item, dict):
             for sub_block in _walk_trie(item):
                 yield sub_block
     yield block
 
 
 def _persist_block(block_node, block_map):
     """produce persistent binary data for a single block
 
     Children block are assumed to be already persisted and present in
     block_map.
     """
     data = tuple(_to_value(block_node.get(i), block_map) for i in range(16))
     return S_BLOCK.pack(*data)
 
 
 def _to_value(item, block_map):
     """persist any value as an integer"""
     if item is None:
         return NO_ENTRY
     elif isinstance(item, dict):
         return block_map[id(item)]
     else:
         return _transform_rev(item)