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1#! /usr/bin/env python3
2
3"""
4combinerefs path
5
6A helper for analyzing PYTHONDUMPREFS output.
7
8When the PYTHONDUMPREFS envar is set in a debug build, at Python shutdown
9time Py_FinalizeEx() prints the list of all live objects twice:  first it
10prints the repr() of each object while the interpreter is still fully intact.
11After cleaning up everything it can, it prints all remaining live objects
12again, but the second time just prints their addresses, refcounts, and type
13names (because the interpreter has been torn down, calling repr methods at
14this point can get into infinite loops or blow up).
15
16Save all this output into a file, then run this script passing the path to
17that file.  The script finds both output chunks, combines them, then prints
18a line of output for each object still alive at the end:
19
20    address refcnt typename repr
21
22address is the address of the object, in whatever format the platform C
23produces for a %p format code.
24
25refcnt is of the form
26
27    "[" ref "]"
28
29when the object's refcount is the same in both PYTHONDUMPREFS output blocks,
30or
31
32    "[" ref_before "->" ref_after "]"
33
34if the refcount changed.
35
36typename is Py_TYPE(object)->tp_name, extracted from the second PYTHONDUMPREFS
37output block.
38
39repr is repr(object), extracted from the first PYTHONDUMPREFS output block.
40CAUTION:  If object is a container type, it may not actually contain all the
41objects shown in the repr:  the repr was captured from the first output block,
42and some of the containees may have been released since then.  For example,
43it's common for the line showing the dict of interned strings to display
44strings that no longer exist at the end of Py_FinalizeEx; this can be recognized
45(albeit painfully) because such containees don't have a line of their own.
46
47The objects are listed in allocation order, with most-recently allocated
48printed first, and the first object allocated printed last.
49
50
51Simple examples:
52
53    00857060 [14] str '__len__'
54
55The str object '__len__' is alive at shutdown time, and both PYTHONDUMPREFS
56output blocks said there were 14 references to it.  This is probably due to
57C modules that intern the string "__len__" and keep a reference to it in a
58file static.
59
60    00857038 [46->5] tuple ()
61
6246-5 = 41 references to the empty tuple were removed by the cleanup actions
63between the times PYTHONDUMPREFS produced output.
64
65    00858028 [1025->1456] str '<dummy key>'
66
67The string '<dummy key>', which is used in dictobject.c to overwrite a real
68key that gets deleted, grew several hundred references during cleanup.  It
69suggests that stuff did get removed from dicts by cleanup, but that the dicts
70themselves are staying alive for some reason. """
71
72import re
73import sys
74
75# Generate lines from fileiter.  If whilematch is true, continue reading
76# while the regexp object pat matches line.  If whilematch is false, lines
77# are read so long as pat doesn't match them.  In any case, the first line
78# that doesn't match pat (when whilematch is true), or that does match pat
79# (when whilematch is false), is lost, and fileiter will resume at the line
80# following it.
81def read(fileiter, pat, whilematch):
82    for line in fileiter:
83        if bool(pat.match(line)) == whilematch:
84            yield line
85        else:
86            break
87
88def combinefile(f):
89    fi = iter(f)
90
91    for line in read(fi, re.compile(r'^Remaining objects:$'), False):
92        pass
93
94    crack = re.compile(r'([a-zA-Z\d]+) \[(\d+)\] (.*)')
95    addr2rc = {}
96    addr2guts = {}
97    before = 0
98    for line in read(fi, re.compile(r'^Remaining object addresses:$'), False):
99        m = crack.match(line)
100        if m:
101            addr, addr2rc[addr], addr2guts[addr] = m.groups()
102            before += 1
103        else:
104            print('??? skipped:', line)
105
106    after = 0
107    for line in read(fi, crack, True):
108        after += 1
109        m = crack.match(line)
110        assert m
111        addr, rc, guts = m.groups() # guts is type name here
112        if addr not in addr2rc:
113            print('??? new object created while tearing down:', line.rstrip())
114            continue
115        print(addr, end=' ')
116        if rc == addr2rc[addr]:
117            print('[%s]' % rc, end=' ')
118        else:
119            print('[%s->%s]' % (addr2rc[addr], rc), end=' ')
120        print(guts, addr2guts[addr])
121
122    print("%d objects before, %d after" % (before, after))
123
124def combine(fname):
125    with open(fname) as f:
126        combinefile(f)
127
128if __name__ == '__main__':
129    combine(sys.argv[1])
130