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#!/usr/bin/env python2.7
# -*- coding: utf-8 -*-
""":synopsis: Interface to the cycle-detecting garbage collector.
"""
"""
A list of objects which the collector found to be unreachable but could not be
freed (uncollectable objects). By default, this list contains only objects with
:meth:`__del__` methods. [#]_ Objects that have :meth:`__del__` methods and are
part of a reference cycle cause the entire reference cycle to be uncollectable,
including objects not necessarily in the cycle but reachable only from it.
Python doesn't collect such cycles automatically because, in general, it isn't
possible for Python to guess a safe order in which to run the :meth:`__del__`
methods. If you know a safe order, you can force the issue by examining the
*garbage* list, and explicitly breaking cycles due to your objects within the
list. Note that these objects are kept alive even so by virtue of being in the
*garbage* list, so they should be removed from *garbage* too. For example,
after breaking cycles, do ``del gc.garbage[:]`` to empty the list. It's
generally better to avoid the issue by not creating cycles containing objects
with :meth:`__del__` methods, and *garbage* can be examined in that case to
verify that no such cycles are being created.
If :const:`DEBUG_SAVEALL` is set, then all unreachable objects will be added to
this list rather than freed.
The following constants are provided for use with :func:`set_debug`:
"""
garbage = None
"""
Print statistics during collection. This information can be useful when tuning
the collection frequency.
"""
DEBUG_STATS = None
"""
Print information on collectable objects found.
"""
DEBUG_COLLECTABLE = None
"""
Print information of uncollectable objects found (objects which are not
reachable but cannot be freed by the collector). These objects will be added to
the ``garbage`` list.
"""
DEBUG_UNCOLLECTABLE = None
"""
When :const:`DEBUG_COLLECTABLE` or :const:`DEBUG_UNCOLLECTABLE` is set, print
information about instance objects found.
"""
DEBUG_INSTANCES = None
"""
When :const:`DEBUG_COLLECTABLE` or :const:`DEBUG_UNCOLLECTABLE` is set, print
information about objects other than instance objects found.
"""
DEBUG_OBJECTS = None
"""
When set, all unreachable objects found will be appended to *garbage* rather
than being freed. This can be useful for debugging a leaking program.
"""
DEBUG_SAVEALL = None
"""
The debugging flags necessary for the collector to print information about a
leaking program (equal to ``DEBUG_COLLECTABLE | DEBUG_UNCOLLECTABLE |
DEBUG_INSTANCES | DEBUG_OBJECTS | DEBUG_SAVEALL``).
"""
DEBUG_LEAK = None
def enable():
"""
Enable automatic garbage collection.
"""
pass
def disable():
"""
Disable automatic garbage collection.
"""
pass
def isenabled():
"""
Returns true if automatic collection is enabled.
"""
pass
def collect(generation):
"""
With no arguments, run a full collection. The optional argument *generation*
may be an integer specifying which generation to collect (from 0 to 2). A
:exc:`ValueError` is raised if the generation number is invalid. The number of
unreachable objects found is returned.
"""
pass
def set_debug(flags):
"""
Set the garbage collection debugging flags. Debugging information will be
written to ``sys.stderr``. See below for a list of debugging flags which can be
combined using bit operations to control debugging.
"""
pass
def get_debug():
"""
Return the debugging flags currently set.
"""
pass
def get_objects():
"""
Returns a list of all objects tracked by the collector, excluding the list
returned.
"""
pass
def set_threshold(threshold0,threshold1,threshold2):
"""
Set the garbage collection thresholds (the collection frequency). Setting
*threshold0* to zero disables collection.
The GC classifies objects into three generations depending on how many
collection sweeps they have survived. New objects are placed in the youngest
generation (generation ``0``). If an object survives a collection it is moved
into the next older generation. Since generation ``2`` is the oldest
generation, objects in that generation remain there after a collection. In
order to decide when to run, the collector keeps track of the number object
allocations and deallocations since the last collection. When the number of
allocations minus the number of deallocations exceeds *threshold0*, collection
starts. Initially only generation ``0`` is examined. If generation ``0`` has
been examined more than *threshold1* times since generation ``1`` has been
examined, then generation ``1`` is examined as well. Similarly, *threshold2*
controls the number of collections of generation ``1`` before collecting
generation ``2``.
"""
pass
def get_count():
"""
Return the current collection counts as a tuple of ``(count0, count1,
count2)``.
"""
pass
def get_threshold():
"""
Return the current collection thresholds as a tuple of ``(threshold0,
threshold1, threshold2)``.
"""
pass
def get_referrers(objs):
"""
Return the list of objects that directly refer to any of objs. This function
will only locate those containers which support garbage collection; extension
types which do refer to other objects but do not support garbage collection will
not be found.
Note that objects which have already been dereferenced, but which live in cycles
and have not yet been collected by the garbage collector can be listed among the
resulting referrers. To get only currently live objects, call :func:`collect`
before calling :func:`get_referrers`.
Care must be taken when using objects returned by :func:`get_referrers` because
some of them could still be under construction and hence in a temporarily
invalid state. Avoid using :func:`get_referrers` for any purpose other than
debugging.
"""
pass
def get_referents(objs):
"""
Return a list of objects directly referred to by any of the arguments. The
referents returned are those objects visited by the arguments' C-level
:attr:`tp_traverse` methods (if any), and may not be all objects actually
directly reachable. :attr:`tp_traverse` methods are supported only by objects
that support garbage collection, and are only required to visit objects that may
be involved in a cycle. So, for example, if an integer is directly reachable
from an argument, that integer object may or may not appear in the result list.
"""
pass
def is_tracked(obj):
"""
Returns True if the object is currently tracked by the garbage collector,
False otherwise. As a general rule, instances of atomic types aren't
tracked and instances of non-atomic types (containers, user-defined
objectsmore) are. However, some type-specific optimizations can be present
in order to suppress the garbage collector footprint of simple instances
(e.g. dicts containing only atomic keys and values)::
>>> gc.is_tracked(0)
False
>>> gc.is_tracked("a")
False
>>> gc.is_tracked([])
True
>>> gc.is_tracked({})
False
>>> gc.is_tracked({"a": 1})
False
>>> gc.is_tracked({"a": []})
True
"""
pass
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