Revert "bpo-31356: Add context manager to temporarily disable GC GH-5495

This reverts commit 72a0d21.

The reverted commit had a few issues so it was unanimously decided
to undo it. See the bpo issue for details.

Author: 1st1

Doc/library/gc.rst

@@ -33,34 +33,6 @@ 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.

Include/internal/mem.h

@@ -116,7 +116,6 @@ 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;

Lib/test/test_gc.py

@@ -1,16 +1,14 @@
 import unittest
 from test.support import (verbose, refcount_test, run_unittest,
                           strip_python_stderr, cpython_only, start_threads,
-                          temp_dir, requires_type_collecting,reap_threads)
+                          temp_dir, requires_type_collecting)
 from test.support.script_helper import assert_python_ok, make_script
 
 import sys
 import time
 import gc
 import weakref
 import threading
-import warnings
-
 
 try:
     from _testcapi import with_tp_del
@@ -1009,73 +1007,6 @@ def __del__(self):
             # 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()

Misc/NEWS.d/3.7.0b1.rst

@@ -196,17 +196,6 @@ by Sanyam Khurana.
 
 ..
 
-.. bpo: 31356
-.. date: 2017-11-02-00-34-42
-.. nonce: 54Lb8U
-.. section: Core and Builtins
-
-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.
-
-..
-
 .. bpo: 31179
 .. date: 2017-08-10-17-32-48
 .. nonce: XcgLYI

Misc/NEWS.d/next/Core and Builtins/2018-02-02-08-50-46.bpo-31356.MNwUOQ.rst

@@ -0,0 +1,2 @@
+Remove the new API added in bpo-31356 (gc.ensure_disabled() context
+manager).

Modules/gcmodule.c

@@ -1067,10 +1067,6 @@ 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;
 }
@@ -1512,102 +1508,6 @@ 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 */
@@ -1648,12 +1548,6 @@ 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);