view mercurial/dagparser.py @ 33171:6d678ab1b10d

revlog: C implementation of delta chain resolution

I've seen revlog._deltachain() appear in a number of performance
profiles. I suspect there are 2 reasons for this:

1. Delta chain resolution performs many index lookups, thus triggering
   population of index tuples. Creating possibly tens of thousands of
   PyObject will have overhead.
2. Delta chain resolution is a tight loop.

By moving delta chain resolution to C, we can defer instantiation
of full index entry tuples and make the loop faster courtesy of
not running in Python.

We can measure the impact to delta chain resolution via
`hg perflogrevision` using the mozilla-central repo with a recent
manifest having delta chain length of 33726:

$ hg perfrevlogrevision -m 364895
! full
! wall 0.367585 comb 0.370000 user 0.340000 sys 0.030000 (best of 27)
! wall 0.357581 comb 0.360000 user 0.350000 sys 0.010000 (best of 28)
! deltachain
! wall 0.010644 comb 0.010000 user 0.010000 sys 0.000000 (best of 270)
! wall 0.000292 comb 0.000000 user 0.000000 sys 0.000000 (best of 8729)

$ hg perfrevlogrevision --cache -m 364895
! deltachain
! wall 0.003904 comb 0.000000 user 0.000000 sys 0.000000 (best of 712)
! wall 0.000284 comb 0.000000 user 0.000000 sys 0.000000 (best of 9926)

The first test measures savings from both not instantiating index
entries and moving to C. The second test (which doesn't clear the
index caches) essentially isolates the benefits of moving from Python
to C. It still shows a 13.7x speedup (versus 36.4x). And there are
multiple milliseconds of savings within the critical path for resolving
revision data. I think that justifies the existence of C code.

A more striking example of the benefits of this change can be
demonstrated by timing `hg debugdeltachain -m` for the mozilla-central
repo:

$ time hg debugdeltachain -m > /dev/null
before:        1057.4s
after:          503.3s
PyPy2.7 5.8.0:  220.0s

It's worth noting that the C code isn't as optimal as it could be.
We're still instantiating a new PyObject for every revision. A future
optimization would be to reuse the PyObject on the cached index tuple.
We could potentially also get wins by using a memory array of raw
integers. There is also room for a delta chain cache on revlog
instances. Of course, the best optimization is to implement revlog
reading outside of Python so Python doesn't need to be concerned
about the relatively expensive index entries and operations on them.

# dagparser.py - parser and generator for concise description of DAGs
#
# Copyright 2010 Peter Arrenbrecht <[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 re
import string

from .i18n import _
from . import error

def parsedag(desc):
    '''parses a DAG from a concise textual description; generates events

    "+n" is a linear run of n nodes based on the current default parent
    "." is a single node based on the current default parent
    "$" resets the default parent to -1 (implied at the start);
        otherwise the default parent is always the last node created
    "<p" sets the default parent to the backref p
    "*p" is a fork at parent p, where p is a backref
    "*p1/p2/.../pn" is a merge of parents p1..pn, where the pi are backrefs
    "/p2/.../pn" is a merge of the preceding node and p2..pn
    ":name" defines a label for the preceding node; labels can be redefined
    "@text" emits an annotation event for text
    "!command" emits an action event for the current node
    "!!my command\n" is like "!", but to the end of the line
    "#...\n" is a comment up to the end of the line

    Whitespace between the above elements is ignored.

    A backref is either
     * a number n, which references the node curr-n, where curr is the current
       node, or
     * the name of a label you placed earlier using ":name", or
     * empty to denote the default parent.

    All string valued-elements are either strictly alphanumeric, or must
    be enclosed in double quotes ("..."), with "\" as escape character.

    Generates sequence of

      ('n', (id, [parentids])) for node creation
      ('l', (id, labelname)) for labels on nodes
      ('a', text) for annotations
      ('c', command) for actions (!)
      ('C', command) for line actions (!!)

    Examples
    --------

    Example of a complex graph (output not shown for brevity):

        >>> len(list(parsedag("""
        ...
        ... +3         # 3 nodes in linear run
        ... :forkhere  # a label for the last of the 3 nodes from above
        ... +5         # 5 more nodes on one branch
        ... :mergethis # label again
        ... <forkhere  # set default parent to labeled fork node
        ... +10        # 10 more nodes on a parallel branch
        ... @stable    # following nodes will be annotated as "stable"
        ... +5         # 5 nodes in stable
        ... !addfile   # custom command; could trigger new file in next node
        ... +2         # two more nodes
        ... /mergethis # merge last node with labeled node
        ... +4         # 4 more nodes descending from merge node
        ...
        ... """)))
        34

    Empty list:

        >>> list(parsedag(""))
        []

    A simple linear run:

        >>> list(parsedag("+3"))
        [('n', (0, [-1])), ('n', (1, [0])), ('n', (2, [1]))]

    Some non-standard ways to define such runs:

        >>> list(parsedag("+1+2"))
        [('n', (0, [-1])), ('n', (1, [0])), ('n', (2, [1]))]

        >>> list(parsedag("+1*1*"))
        [('n', (0, [-1])), ('n', (1, [0])), ('n', (2, [1]))]

        >>> list(parsedag("*"))
        [('n', (0, [-1]))]

        >>> list(parsedag("..."))
        [('n', (0, [-1])), ('n', (1, [0])), ('n', (2, [1]))]

    A fork and a join, using numeric back references:

        >>> list(parsedag("+2*2*/2"))
        [('n', (0, [-1])), ('n', (1, [0])), ('n', (2, [0])), ('n', (3, [2, 1]))]

        >>> list(parsedag("+2<2+1/2"))
        [('n', (0, [-1])), ('n', (1, [0])), ('n', (2, [0])), ('n', (3, [2, 1]))]

    Placing a label:

        >>> list(parsedag("+1 :mylabel +1"))
        [('n', (0, [-1])), ('l', (0, 'mylabel')), ('n', (1, [0]))]

    An empty label (silly, really):

        >>> list(parsedag("+1:+1"))
        [('n', (0, [-1])), ('l', (0, '')), ('n', (1, [0]))]

    Fork and join, but with labels instead of numeric back references:

        >>> list(parsedag("+1:f +1:p2 *f */p2"))
        [('n', (0, [-1])), ('l', (0, 'f')), ('n', (1, [0])), ('l', (1, 'p2')),
         ('n', (2, [0])), ('n', (3, [2, 1]))]

        >>> list(parsedag("+1:f +1:p2 <f +1 /p2"))
        [('n', (0, [-1])), ('l', (0, 'f')), ('n', (1, [0])), ('l', (1, 'p2')),
         ('n', (2, [0])), ('n', (3, [2, 1]))]

    Restarting from the root:

        >>> list(parsedag("+1 $ +1"))
        [('n', (0, [-1])), ('n', (1, [-1]))]

    Annotations, which are meant to introduce sticky state for subsequent nodes:

        >>> list(parsedag("+1 @ann +1"))
        [('n', (0, [-1])), ('a', 'ann'), ('n', (1, [0]))]

        >>> list(parsedag('+1 @"my annotation" +1'))
        [('n', (0, [-1])), ('a', 'my annotation'), ('n', (1, [0]))]

    Commands, which are meant to operate on the most recently created node:

        >>> list(parsedag("+1 !cmd +1"))
        [('n', (0, [-1])), ('c', 'cmd'), ('n', (1, [0]))]

        >>> list(parsedag('+1 !"my command" +1'))
        [('n', (0, [-1])), ('c', 'my command'), ('n', (1, [0]))]

        >>> list(parsedag('+1 !!my command line\\n +1'))
        [('n', (0, [-1])), ('C', 'my command line'), ('n', (1, [0]))]

    Comments, which extend to the end of the line:

        >>> list(parsedag('+1 # comment\\n+1'))
        [('n', (0, [-1])), ('n', (1, [0]))]

    Error:

        >>> try: list(parsedag('+1 bad'))
        ... except Exception, e: print e
        invalid character in dag description: bad...

    '''
    if not desc:
        return

    wordchars = string.ascii_letters + string.digits

    labels = {}
    p1 = -1
    r = 0

    def resolve(ref):
        if not ref:
            return p1
        elif ref[0] in string.digits:
            return r - int(ref)
        else:
            return labels[ref]

    chiter = (c for c in desc)

    def nextch():
        return next(chiter, '\0')

    def nextrun(c, allow):
        s = ''
        while c in allow:
            s += c
            c = nextch()
        return c, s

    def nextdelimited(c, limit, escape):
        s = ''
        while c != limit:
            if c == escape:
                c = nextch()
            s += c
            c = nextch()
        return nextch(), s

    def nextstring(c):
        if c == '"':
            return nextdelimited(nextch(), '"', '\\')
        else:
            return nextrun(c, wordchars)

    c = nextch()
    while c != '\0':
        while c in string.whitespace:
            c = nextch()
        if c == '.':
            yield 'n', (r, [p1])
            p1 = r
            r += 1
            c = nextch()
        elif c == '+':
            c, digs = nextrun(nextch(), string.digits)
            n = int(digs)
            for i in xrange(0, n):
                yield 'n', (r, [p1])
                p1 = r
                r += 1
        elif c in '*/':
            if c == '*':
                c = nextch()
            c, pref = nextstring(c)
            prefs = [pref]
            while c == '/':
                c, pref = nextstring(nextch())
                prefs.append(pref)
            ps = [resolve(ref) for ref in prefs]
            yield 'n', (r, ps)
            p1 = r
            r += 1
        elif c == '<':
            c, ref = nextstring(nextch())
            p1 = resolve(ref)
        elif c == ':':
            c, name = nextstring(nextch())
            labels[name] = p1
            yield 'l', (p1, name)
        elif c == '@':
            c, text = nextstring(nextch())
            yield 'a', text
        elif c == '!':
            c = nextch()
            if c == '!':
                cmd = ''
                c = nextch()
                while c not in '\n\r\0':
                    cmd += c
                    c = nextch()
                yield 'C', cmd
            else:
                c, cmd = nextstring(c)
                yield 'c', cmd
        elif c == '#':
            while c not in '\n\r\0':
                c = nextch()
        elif c == '$':
            p1 = -1
            c = nextch()
        elif c == '\0':
            return # in case it was preceded by whitespace
        else:
            s = ''
            i = 0
            while c != '\0' and i < 10:
                s += c
                i += 1
                c = nextch()
            raise error.Abort(_('invalid character in dag description: '
                               '%s...') % s)

def dagtextlines(events,
                 addspaces=True,
                 wraplabels=False,
                 wrapannotations=False,
                 wrapcommands=False,
                 wrapnonlinear=False,
                 usedots=False,
                 maxlinewidth=70):
    '''generates single lines for dagtext()'''

    def wrapstring(text):
        if re.match("^[0-9a-z]*$", text):
            return text
        return '"' + text.replace('\\', '\\\\').replace('"', '\"') + '"'

    def gen():
        labels = {}
        run = 0
        wantr = 0
        needroot = False
        for kind, data in events:
            if kind == 'n':
                r, ps = data

                # sanity check
                if r != wantr:
                    raise error.Abort(_("expected id %i, got %i") % (wantr, r))
                if not ps:
                    ps = [-1]
                else:
                    for p in ps:
                        if p >= r:
                            raise error.Abort(_("parent id %i is larger than "
                                               "current id %i") % (p, r))
                wantr += 1

                # new root?
                p1 = r - 1
                if len(ps) == 1 and ps[0] == -1:
                    if needroot:
                        if run:
                            yield '+' + str(run)
                            run = 0
                        if wrapnonlinear:
                            yield '\n'
                        yield '$'
                        p1 = -1
                    else:
                        needroot = True
                if len(ps) == 1 and ps[0] == p1:
                    if usedots:
                        yield "."
                    else:
                        run += 1
                else:
                    if run:
                        yield '+' + str(run)
                        run = 0
                    if wrapnonlinear:
                        yield '\n'
                    prefs = []
                    for p in ps:
                        if p == p1:
                            prefs.append('')
                        elif p in labels:
                            prefs.append(labels[p])
                        else:
                            prefs.append(str(r - p))
                    yield '*' + '/'.join(prefs)
            else:
                if run:
                    yield '+' + str(run)
                    run = 0
                if kind == 'l':
                    rid, name = data
                    labels[rid] = name
                    yield ':' + name
                    if wraplabels:
                        yield '\n'
                elif kind == 'c':
                    yield '!' + wrapstring(data)
                    if wrapcommands:
                        yield '\n'
                elif kind == 'C':
                    yield '!!' + data
                    yield '\n'
                elif kind == 'a':
                    if wrapannotations:
                        yield '\n'
                    yield '@' + wrapstring(data)
                elif kind == '#':
                    yield '#' + data
                    yield '\n'
                else:
                    raise error.Abort(_("invalid event type in dag: %s")
                                     % str((type, data)))
        if run:
            yield '+' + str(run)

    line = ''
    for part in gen():
        if part == '\n':
            if line:
                yield line
                line = ''
        else:
            if len(line) + len(part) >= maxlinewidth:
                yield line
                line = ''
            elif addspaces and line and part != '.':
                line += ' '
            line += part
    if line:
        yield line

def dagtext(dag,
            addspaces=True,
            wraplabels=False,
            wrapannotations=False,
            wrapcommands=False,
            wrapnonlinear=False,
            usedots=False,
            maxlinewidth=70):
    '''generates lines of a textual representation for a dag event stream

    events should generate what parsedag() does, so:

      ('n', (id, [parentids])) for node creation
      ('l', (id, labelname)) for labels on nodes
      ('a', text) for annotations
      ('c', text) for commands
      ('C', text) for line commands ('!!')
      ('#', text) for comment lines

    Parent nodes must come before child nodes.

    Examples
    --------

    Linear run:

        >>> dagtext([('n', (0, [-1])), ('n', (1, [0]))])
        '+2'

    Two roots:

        >>> dagtext([('n', (0, [-1])), ('n', (1, [-1]))])
        '+1 $ +1'

    Fork and join:

        >>> dagtext([('n', (0, [-1])), ('n', (1, [0])), ('n', (2, [0])),
        ...          ('n', (3, [2, 1]))])
        '+2 *2 */2'

    Fork and join with labels:

        >>> dagtext([('n', (0, [-1])), ('l', (0, 'f')), ('n', (1, [0])),
        ...          ('l', (1, 'p2')), ('n', (2, [0])), ('n', (3, [2, 1]))])
        '+1 :f +1 :p2 *f */p2'

    Annotations:

        >>> dagtext([('n', (0, [-1])), ('a', 'ann'), ('n', (1, [0]))])
        '+1 @ann +1'

        >>> dagtext([('n', (0, [-1])),
        ...          ('a', 'my annotation'),
        ...          ('n', (1, [0]))])
        '+1 @"my annotation" +1'

    Commands:

        >>> dagtext([('n', (0, [-1])), ('c', 'cmd'), ('n', (1, [0]))])
        '+1 !cmd +1'

        >>> dagtext([('n', (0, [-1])), ('c', 'my command'), ('n', (1, [0]))])
        '+1 !"my command" +1'

        >>> dagtext([('n', (0, [-1])),
        ...          ('C', 'my command line'),
        ...          ('n', (1, [0]))])
        '+1 !!my command line\\n+1'

    Comments:

        >>> dagtext([('n', (0, [-1])), ('#', ' comment'), ('n', (1, [0]))])
        '+1 # comment\\n+1'

        >>> dagtext([])
        ''

    Combining parsedag and dagtext:

        >>> dagtext(parsedag('+1 :f +1 :p2 *f */p2'))
        '+1 :f +1 :p2 *f */p2'

    '''
    return "\n".join(dagtextlines(dag,
                                  addspaces,
                                  wraplabels,
                                  wrapannotations,
                                  wrapcommands,
                                  wrapnonlinear,
                                  usedots,
                                  maxlinewidth))