Suporte a Coleta Cíclica de Lixo¶
O suporte do Python para detectar e coletar o lixo, que envolve referencias circulares, requer suporte dos tipos de objetos que são “contêiners” para outros objetos que também podem ser contêiners. Tipos que não armazenam referências a outros tipos de objetos, ou que apenas armazenam referências a tipos atômicos (como números ou strings), não precisam fornecer nenhum suporte explicito para coleta de lixo.
To create a container type, the tp_flags
field of the type object must
include the Py_TPFLAGS_HAVE_GC
and provide an implementation of the
tp_traverse
handler. If instances of the type are mutable, a
tp_clear
implementation must also be provided.
Py_TPFLAGS_HAVE_GC
Objetos com esse tipo de sinalizador definido devem estar em conformidade com regras documentadas aqui. Por conveniência esses objetos serão referenciados como objetos de contêiner.
Construtores para tipos de contêiner devem obedecer a duas regras:
The memory for the object must be allocated using
PyObject_GC_New
orPyObject_GC_NewVar
.Uma vez que todos os campos que podem conter referências a outros containers foram inicializados, deve-se chamar
PyObject_GC_Track()
.
Da mesma forma, o desalocador para o objeto deve estar em conformidade com regras semelhantes:
Antes que os campos que fazer referência a outros containers sejam invalidados,
PyObject_GC_UnTrack()
deve ser chamado.A memória destinada ao objeto deve ser desalocada usando
PyObject_GC_Del()
.Aviso
If a type adds the Py_TPFLAGS_HAVE_GC, then it must implement at least a
tp_traverse
handler or explicitly use one from its subclass or subclasses.When calling
PyType_Ready()
or some of the APIs that indirectly call it likePyType_FromSpecWithBases()
orPyType_FromSpec()
the interpreter will automatically populate thetp_flags
,tp_traverse
andtp_clear
fields if the type inherits from a class that implements the garbage collector protocol and the child class does not include thePy_TPFLAGS_HAVE_GC
flag.
-
PyObject_GC_New(TYPE, typeobj)¶
Analogous to
PyObject_New
but for container objects with thePy_TPFLAGS_HAVE_GC
flag set.
-
PyObject_GC_NewVar(TYPE, typeobj, size)¶
Analogous to
PyObject_NewVar
but for container objects with thePy_TPFLAGS_HAVE_GC
flag set.
-
PyObject *PyUnstable_Object_GC_NewWithExtraData(PyTypeObject *type, size_t extra_size)¶
- Esta é uma API Instável. Isso pode se alterado sem aviso em lançamentos menores.
Analogous to
PyObject_GC_New
but allocates extra_size bytes at the end of the object (at offsettp_basicsize
). The allocated memory is initialized to zeros, except for thePython object header
.The extra data will be deallocated with the object, but otherwise it is not managed by Python.
Aviso
The function is marked as unstable because the final mechanism for reserving extra data after an instance is not yet decided. For allocating a variable number of fields, prefer using
PyVarObject
andtp_itemsize
instead.Adicionado na versão 3.12.
-
PyObject_GC_Resize(TYPE, op, newsize)¶
Resize an object allocated by
PyObject_NewVar
. Returns the resized object of typeTYPE*
(refers to any C type) orNULL
on failure.op must be of type PyVarObject* and must not be tracked by the collector yet. newsize must be of type
Py_ssize_t
.
-
void PyObject_GC_Track(PyObject *op)¶
- Parte da ABI Estável.
Adds the object op to the set of container objects tracked by the collector. The collector can run at unexpected times so objects must be valid while being tracked. This should be called once all the fields followed by the
tp_traverse
handler become valid, usually near the end of the constructor.
-
int PyObject_IS_GC(PyObject *obj)¶
Returns non-zero if the object implements the garbage collector protocol, otherwise returns 0.
The object cannot be tracked by the garbage collector if this function returns 0.
-
int PyObject_GC_IsTracked(PyObject *op)¶
- Parte da ABI Estável desde a versão 3.9.
Returns 1 if the object type of op implements the GC protocol and op is being currently tracked by the garbage collector and 0 otherwise.
This is analogous to the Python function
gc.is_tracked()
.Adicionado na versão 3.9.
-
int PyObject_GC_IsFinalized(PyObject *op)¶
- Parte da ABI Estável desde a versão 3.9.
Returns 1 if the object type of op implements the GC protocol and op has been already finalized by the garbage collector and 0 otherwise.
This is analogous to the Python function
gc.is_finalized()
.Adicionado na versão 3.9.
-
void PyObject_GC_Del(void *op)¶
- Parte da ABI Estável.
Releases memory allocated to an object using
PyObject_GC_New
orPyObject_GC_NewVar
.
-
void PyObject_GC_UnTrack(void *op)¶
- Parte da ABI Estável.
Remove the object op from the set of container objects tracked by the collector. Note that
PyObject_GC_Track()
can be called again on this object to add it back to the set of tracked objects. The deallocator (tp_dealloc
handler) should call this for the object before any of the fields used by thetp_traverse
handler become invalid.
Alterado na versão 3.8: The _PyObject_GC_TRACK()
and _PyObject_GC_UNTRACK()
macros
have been removed from the public C API.
The tp_traverse
handler accepts a function parameter of this type:
-
typedef int (*visitproc)(PyObject *object, void *arg)¶
- Parte da ABI Estável.
Type of the visitor function passed to the
tp_traverse
handler. The function should be called with an object to traverse as object and the third parameter to thetp_traverse
handler as arg. The Python core uses several visitor functions to implement cyclic garbage detection; it’s not expected that users will need to write their own visitor functions.
The tp_traverse
handler must have the following type:
-
typedef int (*traverseproc)(PyObject *self, visitproc visit, void *arg)¶
- Parte da ABI Estável.
Traversal function for a container object. Implementations must call the visit function for each object directly contained by self, with the parameters to visit being the contained object and the arg value passed to the handler. The visit function must not be called with a
NULL
object argument. If visit returns a non-zero value that value should be returned immediately.
To simplify writing tp_traverse
handlers, a Py_VISIT()
macro is
provided. In order to use this macro, the tp_traverse
implementation
must name its arguments exactly visit and arg:
-
void Py_VISIT(PyObject *o)¶
If o is not
NULL
, call the visit callback, with arguments o and arg. If visit returns a non-zero value, then return it. Using this macro,tp_traverse
handlers look like:static int my_traverse(Noddy *self, visitproc visit, void *arg) { Py_VISIT(self->foo); Py_VISIT(self->bar); return 0; }
The tp_clear
handler must be of the inquiry
type, or NULL
if the object is immutable.
-
typedef int (*inquiry)(PyObject *self)¶
- Parte da ABI Estável.
Drop references that may have created reference cycles. Immutable objects do not have to define this method since they can never directly create reference cycles. Note that the object must still be valid after calling this method (don’t just call
Py_DECREF()
on a reference). The collector will call this method if it detects that this object is involved in a reference cycle.
Controlando o estado do coletor de lixo¶
The C-API provides the following functions for controlling garbage collection runs.
-
Py_ssize_t PyGC_Collect(void)¶
- Parte da ABI Estável.
Perform a full garbage collection, if the garbage collector is enabled. (Note that
gc.collect()
runs it unconditionally.)Returns the number of collected + unreachable objects which cannot be collected. If the garbage collector is disabled or already collecting, returns
0
immediately. Errors during garbage collection are passed tosys.unraisablehook
. This function does not raise exceptions.
-
int PyGC_Enable(void)¶
- Parte da ABI Estável desde a versão 3.10.
Enable the garbage collector: similar to
gc.enable()
. Returns the previous state, 0 for disabled and 1 for enabled.Adicionado na versão 3.10.
-
int PyGC_Disable(void)¶
- Parte da ABI Estável desde a versão 3.10.
Disable the garbage collector: similar to
gc.disable()
. Returns the previous state, 0 for disabled and 1 for enabled.Adicionado na versão 3.10.
-
int PyGC_IsEnabled(void)¶
- Parte da ABI Estável desde a versão 3.10.
Query the state of the garbage collector: similar to
gc.isenabled()
. Returns the current state, 0 for disabled and 1 for enabled.Adicionado na versão 3.10.
Querying Garbage Collector State¶
The C-API provides the following interface for querying information about the garbage collector.
-
void PyUnstable_GC_VisitObjects(gcvisitobjects_t callback, void *arg)¶
- Esta é uma API Instável. Isso pode se alterado sem aviso em lançamentos menores.
Run supplied callback on all live GC-capable objects. arg is passed through to all invocations of callback.
Aviso
If new objects are (de)allocated by the callback it is undefined if they will be visited.
Garbage collection is disabled during operation. Explicitly running a collection in the callback may lead to undefined behaviour e.g. visiting the same objects multiple times or not at all.
Adicionado na versão 3.12.
-
typedef int (*gcvisitobjects_t)(PyObject *object, void *arg)¶
Type of the visitor function to be passed to
PyUnstable_GC_VisitObjects()
. arg is the same as the arg passed toPyUnstable_GC_VisitObjects
. Return0
to continue iteration, return1
to stop iteration. Other return values are reserved for now so behavior on returning anything else is undefined.Adicionado na versão 3.12.