| 1 | #!/usr/bin/env python2
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| 2 | """
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| 3 | gc_stack_roots.py
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| 4 | """
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| 5 | from __future__ import print_function
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| 6 |
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| 7 | import os
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| 8 |
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| 9 | from mycpp import mylib
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| 10 | from mycpp.mylib import log
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| 11 |
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| 12 | from typing import Any, List
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| 13 | """
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| 14 | Helpers
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| 15 | """
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| 16 |
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| 17 |
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| 18 | def print_list(l):
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| 19 | # type: (List[str]) -> None
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| 20 | for s in l:
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| 21 | print(s)
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| 22 |
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| 23 |
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| 24 | def calls_collect():
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| 25 | # type: () -> None
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| 26 | mylib.MaybeCollect()
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| 27 |
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| 28 |
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| 29 | def ignore_and_collect(l):
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| 30 | # type: (List[str]) -> None
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| 31 | mylib.MaybeCollect()
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| 32 |
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| 33 |
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| 34 | def collect_and_return(l):
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| 35 | # type: (List[str]) -> List[str]
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| 36 | mylib.MaybeCollect()
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| 37 | return l
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| 38 |
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| 39 |
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| 40 | def collect_and_slice(s):
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| 41 | # type: (str) -> str
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| 42 | mylib.MaybeCollect()
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| 43 | return s[1:]
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| 44 |
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| 45 |
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| 46 | class ctx_Stasher(object):
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| 47 |
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| 48 | def __init__(self, l):
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| 49 | # type: (List[str]) -> None
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| 50 | self.l = l
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| 51 |
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| 52 | def __enter__(self):
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| 53 | # type: () -> None
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| 54 | pass
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| 55 |
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| 56 | def __exit__(self, type, value, traceback):
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| 57 | # type: (Any, Any, Any) -> None
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| 58 | print_list(self.l)
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| 59 |
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| 60 |
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| 61 | """
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| 62 | Test cases
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| 63 | """
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| 64 |
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| 65 |
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| 66 | def no_collect():
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| 67 | # type: () -> None
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| 68 | """
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| 69 | There's no need to gernate any stack roots in this case. There is no threat
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| 70 | of anything being swept.
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| 71 | """
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| 72 | l = ['no', 'collect'] # type: List[str]
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| 73 | print_list(l)
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| 74 |
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| 75 |
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| 76 | def simple_collect():
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| 77 | # type: () -> None
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| 78 | """
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| 79 | Only l1 needs to be rooted here. l2 is not live after the call to collect.
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| 80 | """
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| 81 | l1 = ['foo', 'bar'] # type: List[str]
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| 82 | l2 = ['bing', 'bong'] # type: List[str]
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| 83 | print_list(l2)
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| 84 | if len(l1):
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| 85 | mylib.MaybeCollect()
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| 86 |
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| 87 | print_list(l1)
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| 88 |
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| 89 |
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| 90 | def indirect_collect():
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| 91 | # type: () -> None
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| 92 | """
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| 93 | l should be rooted since it is live after an indirect call to collect.
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| 94 | """
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| 95 | l = ['indirect', 'collect']
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| 96 | calls_collect()
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| 97 | print_list(l)
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| 98 |
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| 99 |
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| 100 | def arg_roots():
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| 101 | # type: () -> None
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| 102 | """
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| 103 | If a function might collect it should unconditionally root its arguments.
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| 104 | It should root them even if it doesn't use them directly because we can't
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| 105 | gaurantee that the caller will even have been able to root them, e.g. in the
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| 106 | case of function composition or an arugment being constructed inline.
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| 107 | """
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| 108 | l1 = ['OK'] # Should be rooted by ignore_and_collect().
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| 109 | ignore_and_collect(l1)
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| 110 | print_list(l1)
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| 111 |
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| 112 | # The temporary list should be rooted by collect_and_return().
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| 113 | l2 = collect_and_return(['not', 'swept'])
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| 114 | print_list(l2)
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| 115 |
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| 116 |
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| 117 | def alias():
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| 118 | # type: () -> None
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| 119 | """
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| 120 | Only one of l1 and l2 needs to be rooted here. In this case we should choose
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| 121 | l2 since it is live after the collector runs.
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| 122 | """
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| 123 | l1 = ['foo', 'bar'] # type: List[str]
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| 124 | l2 = l1
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| 125 | mylib.MaybeCollect()
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| 126 | print_list(l2)
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| 127 |
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| 128 |
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| 129 | def collect_scoped_resource():
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| 130 | # type: () -> None
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| 131 | """
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| 132 | Similar to function arguments, members of context managers should be rooted
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| 133 | by their constructors. However, unlike normal functions these constructors
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| 134 | should do so even if they don't cause a collection. The caller might trigger
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| 135 | garbage collection while the manager is still in scope and the members will
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| 136 | get swept if they weren't already rooted further up in the call stack.
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| 137 | """
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| 138 | with ctx_Stasher(['context', 'member']) as ctx:
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| 139 | mylib.MaybeCollect()
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| 140 |
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| 141 |
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| 142 | def collect_in_loop():
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| 143 | # type: () -> None
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| 144 | """
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| 145 | Temporary variables used in loops should be rooted if a collection might
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| 146 | happen within the loop body.
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| 147 | """
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| 148 | for s in ['watch', 'out']:
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| 149 | mylib.MaybeCollect()
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| 150 | print(s)
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| 151 |
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| 152 |
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| 153 | def collect_in_comprehension():
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| 154 | # type: () -> None
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| 155 | """
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| 156 | Temporary variables used in list comprehensions should be rooted if a
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| 157 | collection might happen.
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| 158 | """
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| 159 | l = ['%s' % collect_and_slice(s)
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| 160 | for s in ['foo', 'bar']] # type: List[str]
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| 161 | for s in l:
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| 162 | print(s)
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| 163 |
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| 164 |
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| 165 | def run_tests():
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| 166 | # type: () -> None
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| 167 | no_collect()
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| 168 | simple_collect()
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| 169 | indirect_collect()
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| 170 | arg_roots()
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| 171 | alias()
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| 172 | collect_scoped_resource()
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| 173 | # TODO: maybe move these two to invalid examples if we decide to disallow.
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| 174 | #collect_in_loop()
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| 175 | #collect_in_comprehension()
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| 176 |
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| 177 |
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| 178 | def run_benchmarks():
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| 179 | # type: () -> None
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| 180 | pass
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| 181 |
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| 182 |
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| 183 | if __name__ == '__main__':
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| 184 | if os.getenv('BENCHMARK'):
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| 185 | log('Benchmarking...')
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| 186 | run_benchmarks()
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| 187 | else:
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| 188 | run_tests()
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