symbian-qemu-0.9.1-12/python-2.6.1/Misc/find_recursionlimit.py
author martin.trojer@nokia.com
Fri, 31 Jul 2009 15:01:17 +0100
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#! /usr/bin/env python
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"""Find the maximum recursion limit that prevents interpreter termination.
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This script finds the maximum safe recursion limit on a particular
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platform.  If you need to change the recursion limit on your system,
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this script will tell you a safe upper bound.  To use the new limit,
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call sys.setrecursionlimit().
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This module implements several ways to create infinite recursion in
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Python.  Different implementations end up pushing different numbers of
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C stack frames, depending on how many calls through Python's abstract
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C API occur.
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After each round of tests, it prints a message:
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"Limit of NNNN is fine".
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The highest printed value of "NNNN" is therefore the highest potentially
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safe limit for your system (which depends on the OS, architecture, but also
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the compilation flags). Please note that it is practically impossible to
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test all possible recursion paths in the interpreter, so the results of
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this test should not be trusted blindly -- although they give a good hint
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of which values are reasonable.
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NOTE: When the C stack space allocated by your system is exceeded due
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to excessive recursion, exact behaviour depends on the platform, although
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the interpreter will always fail in a likely brutal way: either a
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segmentation fault, a MemoryError, or just a silent abort.
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NB: A program that does not use __methods__ can set a higher limit.
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"""
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import sys
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import itertools
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class RecursiveBlowup1:
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    def __init__(self):
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        self.__init__()
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def test_init():
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    return RecursiveBlowup1()
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class RecursiveBlowup2:
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    def __repr__(self):
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        return repr(self)
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def test_repr():
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    return repr(RecursiveBlowup2())
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class RecursiveBlowup4:
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    def __add__(self, x):
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        return x + self
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def test_add():
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    return RecursiveBlowup4() + RecursiveBlowup4()
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class RecursiveBlowup5:
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    def __getattr__(self, attr):
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        return getattr(self, attr)
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def test_getattr():
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    return RecursiveBlowup5().attr
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class RecursiveBlowup6:
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    def __getitem__(self, item):
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        return self[item - 2] + self[item - 1]
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def test_getitem():
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    return RecursiveBlowup6()[5]
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def test_recurse():
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    return test_recurse()
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def test_cpickle(_cache={}):
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    try:
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        import cPickle
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    except ImportError:
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        print "cannot import cPickle, skipped!"
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        return
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    l = None
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    for n in itertools.count():
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        try:
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            l = _cache[n]
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            continue  # Already tried and it works, let's save some time
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        except KeyError:
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            for i in range(100):
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                l = [l]
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        cPickle.dumps(l, protocol=-1)
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        _cache[n] = l
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def check_limit(n, test_func_name):
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    sys.setrecursionlimit(n)
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    if test_func_name.startswith("test_"):
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        print test_func_name[5:]
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    else:
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        print test_func_name
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    test_func = globals()[test_func_name]
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    try:
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        test_func()
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    # AttributeError can be raised because of the way e.g. PyDict_GetItem()
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    # silences all exceptions and returns NULL, which is usually interpreted
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    # as "missing attribute".
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    except (RuntimeError, AttributeError):
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        pass
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    else:
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        print "Yikes!"
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limit = 1000
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while 1:
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    check_limit(limit, "test_recurse")
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    check_limit(limit, "test_add")
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    check_limit(limit, "test_repr")
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    check_limit(limit, "test_init")
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    check_limit(limit, "test_getattr")
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    check_limit(limit, "test_getitem")
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    check_limit(limit, "test_cpickle")
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    print "Limit of %d is fine" % limit
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    limit = limit + 100