New submission from STINNER Victor:
When I read Serhiy Storshaka's idea in issue #29878, it recalled me an old idea
of writing a generalization of the _Py_IDENTIFIER() API.
_Py_IDENTIFIER is an API to initialize a static string variable once. The
_Py_Identifier structure has a "next" field to create a single-linked chained
list. It allows to clear all variables at exit in
_PyUnicode_ClearStaticStrings().
I propose a similar API but for any PyObject* object, to be able to clear all
static variables at exit. It should help to release all memory in Py_Finalize()
and have a safer Python finalization.
See attached pull request for the API itself.
"Static variables" in C are variables with a limited scope: a single C file or
a single function.
It seems like the API can remove some lines of code. Example of patch:
@@ -1452,14 +1450,14 @@ compiler_mod(struct compiler *c, mod_ty mod)
{
PyCodeObject *co;
int addNone = 1;
- static PyObject *module;
- if (!module) {
- module = PyUnicode_InternFromString("<module>");
- if (!module)
- return NULL;
+ _Py_STATICVAR(module);
+
+ if (_PY_STATICVAR_INIT(&module, PyUnicode_InternFromString("<module>"))) {
+ return 0;
}
+
/* Use 0 for firstlineno initially, will fixup in assemble(). */
- if (!compiler_enter_scope(c, module, COMPILER_SCOPE_MODULE, mod, 0))
+ if (!compiler_enter_scope(c, module.obj, COMPILER_SCOPE_MODULE, mod, 0))
return NULL;
switch (mod->kind) {
case Module_kind:
--
Drawbacks of the API:
* It adds one pointer per static variables, so increase the memory footprint of
8 bytes per variable
* It requires to write "var.obj" instead of just "var" to access the Python
object
The API doesn't try to remove duplicated objects. I consider that it's not an
issue since functions like PyLong_FromLong(<small int>) and
PyUnicode_InternFromString("c string") already do it for us. Some functions
create mutable variables like PyImport_Import() which creates an empty list.
--
Note: Eric Snow proposed a solution "solving multi-core Python":
* https://mail.python.org/pipermail/python-ideas/2015-June/034177.html
* http://ericsnowcurrently.blogspot.fr/2016/09/solving-mutli-core-python.html
I'm not sure if this API would help or not to implement such idea, but Eric's
project is experimental and wasn't taken in account when designing the API.
----------
components: Interpreter Core
messages: 289999
nosy: haypo
priority: normal
severity: normal
status: open
title: Add a new private API for "static C variables" (_PyStaticVar) to clear
them at exit
type: resource usage
versions: Python 3.7
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Python tracker <[email protected]>
<http://bugs.python.org/issue29881>
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