bpo-1635741: Clean sysdict and builtins of interpreter

[shihai1991]

https://bugs.python.org/issue1635741

[shihai1991]

The master benchmark:
sys.gettotalrefcount: 14779
sys.gettotalrefcount: 19024
sys.gettotalrefcount: 23269
sys.gettotalrefcount: 27514
sys.gettotalrefcount: 31759
sys.gettotalrefcount: 36004
sys.gettotalrefcount: 40249
sys.gettotalrefcount: 44494
sys.gettotalrefcount: 48739
sys.gettotalrefcount: 52984

After this PR:
sys.gettotalrefcount: 14295
sys.gettotalrefcount: 18056
sys.gettotalrefcount: 21817
sys.gettotalrefcount: 25578
sys.gettotalrefcount: 29339
sys.gettotalrefcount: 33100
sys.gettotalrefcount: 36861
sys.gettotalrefcount: 40622
sys.gettotalrefcount: 44383
sys.gettotalrefcount: 48144

[shihai1991]

@vstinner Hi, victor, pls take a look after your vacation, thanks.

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @corona10 for commit 137967a 🤖

If you want to schedule another build, you need to add the ":hammer: test-with-buildbots" label again.

[shihai1991]

thanks Dong-hee Na for your label ;)

[vstinner]

I don't see the point of adding two local variables, why not accessing directly the structure member?

Suggested change

	PyDict_Clear(sysdict);
	PyDict_Clear(interp->sysdict);

Same remark on folowing line.

[shihai1991]

interp->sysdict and interp->builtins will be cleared before this line. https://github.com/python/cpython/blob/master/Python/pystate.c#L297-L298

[vstinner]

Aha, I didn't notice. In this case, I suggest to move Py_CLEAR(interp->sysdict) and Py_CLEAR(interp->builtins) at the end. Something like:

PyDict_Clear(interp->sysdict);
PyDict_Clear(interp->builtins);
Py_CLEAR(interp->sysdict)
Py_CLEAR(interp->builtins);

[shihai1991]

updated. And I delete the description info.

[vstinner]

The master benchmark:

What is this benchmark? Which code did you run?

[shihai1991]

The master benchmark:

What is this benchmark? Which code did you run?

Hm, This should not be called as benchmark. I compare the refleak of this PR with the refleak of master branch. I use debug mode to test it. Because the testcase in https://bugs.python.org/issue1635741#msg355187 use _Py_GetRefTotal()

[vstinner]

Since few people care about subinterpreters, I don't think that it's worth it to document this internal change in a NEWS entry: I added "skip news" label.

[vstinner]

LGTM.

[shihai1991]

thanks, victor.