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""" |
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Module for testing automatic garbage collection of objects |
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.. autosummary:: |
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:toctree: generated/ |
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set_gc_state - enable or disable garbage collection |
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gc_state - context manager for given state of garbage collector |
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assert_deallocated - context manager to check for circular references on object |
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""" |
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import weakref |
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import gc |
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from contextlib import contextmanager |
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from platform import python_implementation |
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__all__ = ['set_gc_state', 'gc_state', 'assert_deallocated'] |
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IS_PYPY = python_implementation() == 'PyPy' |
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class ReferenceError(AssertionError): |
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pass |
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def set_gc_state(state): |
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""" Set status of garbage collector """ |
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if gc.isenabled() == state: |
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return |
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if state: |
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gc.enable() |
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else: |
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gc.disable() |
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@contextmanager |
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def gc_state(state): |
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""" Context manager to set state of garbage collector to `state` |
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Parameters |
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---------- |
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state : bool |
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True for gc enabled, False for disabled |
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Examples |
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-------- |
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>>> with gc_state(False): |
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... assert not gc.isenabled() |
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>>> with gc_state(True): |
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... assert gc.isenabled() |
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""" |
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orig_state = gc.isenabled() |
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set_gc_state(state) |
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yield |
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set_gc_state(orig_state) |
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@contextmanager |
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def assert_deallocated(func, *args, **kwargs): |
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"""Context manager to check that object is deallocated |
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This is useful for checking that an object can be freed directly by |
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reference counting, without requiring gc to break reference cycles. |
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GC is disabled inside the context manager. |
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This check is not available on PyPy. |
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Parameters |
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---------- |
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func : callable |
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Callable to create object to check |
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\\*args : sequence |
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positional arguments to `func` in order to create object to check |
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\\*\\*kwargs : dict |
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keyword arguments to `func` in order to create object to check |
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Examples |
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-------- |
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>>> class C: pass |
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>>> with assert_deallocated(C) as c: |
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... # do something |
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... del c |
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>>> class C: |
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... def __init__(self): |
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... self._circular = self # Make circular reference |
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>>> with assert_deallocated(C) as c: #doctest: +IGNORE_EXCEPTION_DETAIL |
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... # do something |
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... del c |
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Traceback (most recent call last): |
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... |
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ReferenceError: Remaining reference(s) to object |
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""" |
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if IS_PYPY: |
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raise RuntimeError("assert_deallocated is unavailable on PyPy") |
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with gc_state(False): |
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obj = func(*args, **kwargs) |
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ref = weakref.ref(obj) |
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yield obj |
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del obj |
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if ref() is not None: |
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raise ReferenceError("Remaining reference(s) to object") |
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