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bpo-31356: Add context manager to temporarily disable GC (GH-4224)

This commit is contained in:
Pablo Galindo 2018-01-29 20:37:09 +00:00 committed by Raymond Hettinger
parent 0cd6bca655
commit 72a0d218dc
5 changed files with 208 additions and 1 deletions
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28
Doc/library/gc.rst
View File

@ -33,6 +33,34 @@ The :mod:`gc` module provides the following functions:
Disable automatic garbage collection.
.. class:: ensure_disabled()
Return a context manager object that disables the garbage collector and reenables the previous
state upon completion of the block. This is basically equivalent to::
from gc import enable, disable, isenabled
@contextmanager
def ensure_disabled():
was_enabled_previously = isenabled()
gc.disable()
yield
if was_enabled_previously:
gc.enable()
And lets you write code like this::
with ensure_disabled():
run_some_timing()
with ensure_disabled():
# do_something_that_has_real_time_guarantees
# such as a pair trade, robotic braking, etc
without needing to explicitly enable and disable the garbage collector yourself.
This context manager is implemented in C to assure atomicity, thread safety and speed.
.. function:: isenabled()
Returns true if automatic collection is enabled.

1
Include/internal/mem.h
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@ -116,6 +116,7 @@ struct _gc_runtime_state {
int enabled;
int debug;
long disabled_threads;
/* linked lists of container objects */
struct gc_generation generations[NUM_GENERATIONS];
PyGC_Head *generation0;

71
Lib/test/test_gc.py
View File

@ -1,7 +1,7 @@
import unittest
from test.support import (verbose, refcount_test, run_unittest,
strip_python_stderr, cpython_only, start_threads,
temp_dir, requires_type_collecting)
temp_dir, requires_type_collecting,reap_threads)
from test.support.script_helper import assert_python_ok, make_script
import sys
@ -9,6 +9,8 @@ import time
import gc
import weakref
import threading
import warnings
try:
from _testcapi import with_tp_del
@ -1007,6 +1009,73 @@ class GCTogglingTests(unittest.TestCase):
# empty __dict__.
self.assertEqual(x, None)
def test_ensure_disabled(self):
original_status = gc.isenabled()
with gc.ensure_disabled():
inside_status = gc.isenabled()
after_status = gc.isenabled()
self.assertEqual(original_status, True)
self.assertEqual(inside_status, False)
self.assertEqual(after_status, True)
def test_ensure_disabled_with_gc_disabled(self):
gc.disable()
original_status = gc.isenabled()
with gc.ensure_disabled():
inside_status = gc.isenabled()
after_status = gc.isenabled()
self.assertEqual(original_status, False)
self.assertEqual(inside_status, False)
self.assertEqual(after_status, False)
@reap_threads
def test_ensure_disabled_thread(self):
thread_original_status = None
thread_inside_status = None
thread_after_status = None
def disabling_thread():
nonlocal thread_original_status
nonlocal thread_inside_status
nonlocal thread_after_status
thread_original_status = gc.isenabled()
with gc.ensure_disabled():
time.sleep(0.01)
thread_inside_status = gc.isenabled()
thread_after_status = gc.isenabled()
original_status = gc.isenabled()
with warnings.catch_warnings(record=True) as w, gc.ensure_disabled():
inside_status_before_thread = gc.isenabled()
thread = threading.Thread(target=disabling_thread)
thread.start()
inside_status_after_thread = gc.isenabled()
after_status = gc.isenabled()
thread.join()
self.assertEqual(len(w), 1)
self.assertTrue(issubclass(w[-1].category, RuntimeWarning))
self.assertEqual("Garbage collector enabled while another thread is "
"inside gc.ensure_enabled", str(w[-1].message))
self.assertEqual(original_status, True)
self.assertEqual(inside_status_before_thread, False)
self.assertEqual(thread_original_status, False)
self.assertEqual(thread_inside_status, True)
self.assertEqual(thread_after_status, False)
self.assertEqual(inside_status_after_thread, False)
self.assertEqual(after_status, True)
def test_main():
enabled = gc.isenabled()
gc.disable()

3
Misc/NEWS.d/next/Core and Builtins/2017-11-02-00-34-42.bpo-31356.54Lb8U.rst Normal file
View File

@ -0,0 +1,3 @@
Add a new contextmanager to the gc module that temporarily disables the GC
and restores the previous state. The implementation is done in C to assure
atomicity and speed.

106
Modules/gcmodule.c
View File

@ -1067,6 +1067,10 @@ static PyObject *
gc_enable_impl(PyObject *module)
/*[clinic end generated code: output=45a427e9dce9155c input=81ac4940ca579707]*/
{
if(_PyRuntime.gc.disabled_threads){
PyErr_WarnEx(PyExc_RuntimeWarning, "Garbage collector enabled while another "
"thread is inside gc.ensure_enabled",1);
}
_PyRuntime.gc.enabled = 1;
Py_RETURN_NONE;
}
@ -1508,6 +1512,102 @@ static PyMethodDef GcMethods[] = {
{NULL, NULL} /* Sentinel */
};
typedef struct {
PyObject_HEAD
int previous_gc_state;
} ensure_disabled_object;
static void
ensure_disabled_object_dealloc(ensure_disabled_object *m_obj)
{
Py_TYPE(m_obj)->tp_free((PyObject*)m_obj);
}
static PyObject *
ensure_disabled__enter__method(ensure_disabled_object *self, PyObject *args)
{
PyGILState_STATE gstate = PyGILState_Ensure();
++_PyRuntime.gc.disabled_threads;
self->previous_gc_state = _PyRuntime.gc.enabled;
gc_disable_impl(NULL);
PyGILState_Release(gstate);
Py_RETURN_NONE;
}
static PyObject *
ensure_disabled__exit__method(ensure_disabled_object *self, PyObject *args)
{
PyGILState_STATE gstate = PyGILState_Ensure();
--_PyRuntime.gc.disabled_threads;
if(self->previous_gc_state){
gc_enable_impl(NULL);
}else{
gc_disable_impl(NULL);
}
PyGILState_Release(gstate);
Py_RETURN_NONE;
}
static struct PyMethodDef ensure_disabled_object_methods[] = {
{"__enter__", (PyCFunction) ensure_disabled__enter__method, METH_NOARGS},
{"__exit__", (PyCFunction) ensure_disabled__exit__method, METH_VARARGS},
{NULL, NULL} /* sentinel */
};
static PyObject *
new_disabled_obj(PyTypeObject *type, PyObject *args, PyObject *kwdict){
ensure_disabled_object *self;
self = (ensure_disabled_object *)type->tp_alloc(type, 0);
return (PyObject *) self;
};
static PyTypeObject gc_ensure_disabled_type = {
PyVarObject_HEAD_INIT(NULL, 0)
"gc.ensure_disabled", /* tp_name */
sizeof(ensure_disabled_object), /* tp_size */
0, /* tp_itemsize */
/* methods */
(destructor) ensure_disabled_object_dealloc,/* tp_dealloc */
0, /* tp_print */
0, /* tp_getattr */
0, /* tp_setattr */
0, /* tp_reserved */
0, /* tp_repr */
0, /* tp_as_number */
0, /*tp_as_sequence*/
0, /*tp_as_mapping*/
0, /*tp_hash*/
0, /*tp_call*/
0, /*tp_str*/
PyObject_GenericGetAttr, /*tp_getattro*/
0, /*tp_setattro*/
0, /*tp_as_buffer*/
Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE, /*tp_flags*/
0, /*tp_doc*/
0, /* tp_traverse */
0, /* tp_clear */
0, /* tp_richcompare */
0, /* tp_weaklistoffset */
0, /* tp_iter */
0, /* tp_iternext */
ensure_disabled_object_methods, /* tp_methods */
0, /* tp_members */
0, /* tp_getset */
0, /* tp_base */
0, /* tp_dict */
0, /* tp_descr_get */
0, /* tp_descr_set */
0, /* tp_dictoffset */
0, /* tp_init */
PyType_GenericAlloc, /* tp_alloc */
new_disabled_obj, /* tp_new */
PyObject_Del, /* tp_free */
};
static struct PyModuleDef gcmodule = {
PyModuleDef_HEAD_INIT,
"gc", /* m_name */
@ -1548,6 +1648,12 @@ PyInit_gc(void)
if (PyModule_AddObject(m, "callbacks", _PyRuntime.gc.callbacks) < 0)
return NULL;
if (PyType_Ready(&gc_ensure_disabled_type) < 0)
return NULL;
if (PyModule_AddObject(m, "ensure_disabled", (PyObject*) &gc_ensure_disabled_type) < 0)
return NULL;
#define ADD_INT(NAME) if (PyModule_AddIntConstant(m, #NAME, NAME) < 0) return NULL
ADD_INT(DEBUG_STATS);
ADD_INT(DEBUG_COLLECTABLE);