Tools/scripts/combinerefs.py

#! /usr/bin/env python

"""
combinerefs path

A helper for analyzing PYTHONDUMPREFS output.

When the PYTHONDUMPREFS envar is set in a debug build, at Python shutdown
time Py_Finalize() prints the list of all live objects twice:  first it
prints the repr() of each object while the interpreter is still fully intact.
After cleaning up everything it can, it prints all remaining live objects
again, but the second time just prints their addresses, refcounts, and type
names.

Save all this output into a file, then run this script passing the path to
that file.  The script finds both output chunks, combines them, then prints
a line of output for each object still alive at the end:

    address refcnt typename repr

address is the address of the object, in whatever format the platform C
produces for a %p format code.

refcnt is of the form

    "[" ref "]"

when the object's refcount is the same in both PYTHONDUMPREFS output blocks,
or

    "[" ref_before "->" ref_after "]"

if the refcount changed.

typename is object->ob_type->tp_name, extracted from the second PYTHONDUMPREFS
output block.

repr is repr(object), extracted from the first PYTHONDUMPREFS output block.

The objects are listed in allocation order, with most-recently allocated
printed first, and the first object allocated printed last.


Simple examples:

    00857060 [14] str '__len__'

The str object '__len__' is alive at shutdown time, and both PYTHONDUMPREFS
output blocks said there were 14 references to it.  This is probably due to
C modules that intern the string "__len__" and keep a reference to it in a
file static.

    00857038 [46->5] tuple ()

46-5 = 41 references to the empty tuple were removed by the cleanup actions
between the times PYTHONDUMPREFS produced output.

    00858028 [1025->1456] str '<dummy key>'

The string '<dummy key>', which is used in dictobject.c as the name of the
dummy key that overwrites a real key that gets deleted, actually grew
several hundred references during cleanup.  It suggests that stuff did get
removed from dicts by cleanup, but that the dicts themselves are staying
alive for some reason.
"""

import re
import sys

# Generate lines from fileiter.  If whilematch is true, continue reading
# while the regexp object pat matches line.  If whilematch is false, lines
# are read so long as pat doesn't match them.  In any case, the first line
# that doesn't match pat (when whilematch is true), or that does match pat
# (when whilematch is false), is lost, and fileiter will resume at the line
# following it.
def read(fileiter, pat, whilematch):
    result = []
    for line in fileiter:
        if bool(pat.match(line)) == whilematch:
            result.append(line)
        else:
            break
    return result

def combine(fname):
    f = file(fname)
    fi = iter(f)

    for line in read(fi, re.compile(r'^Remaining objects:$'), False):
        pass

    crack = re.compile(r'([a-zA-Z\d]+) \[(\d+)\] (.*)')
    addr2rc = {}
    addr2guts = {}
    before = 0
    for line in read(fi, re.compile(r'^Remaining object addresses:$'), False):
        m = crack.match(line)
        if m:
            addr, addr2rc[addr], addr2guts[addr] = m.groups()
            before += 1
        else:
            print '??? skipped:', line

    after = 0
    for line in read(fi, crack, True):
        after += 1
        m = crack.match(line)
        assert m
        addr, rc, guts = m.groups() # guts is type name here
        if addr not in addr2rc:
            print '??? new object created while tearing down:', line
            continue
        print addr,
        if rc == addr2rc[addr]:
            print '[%s]' % rc,
        else:
            print '[%s->%s]' % (addr2rc[addr], rc),
        print guts, addr2guts[addr]

    f.close()
    print "%d objects before, %d after" % (before, after)

if __name__ == '__main__':
    combine(sys.argv[1])