New submission from Inada Naoki <songofaca...@gmail.com>:
I checked stack usage for bpo-46600 and found this two functions use a lot of
stack.
os_setgroups: 262200 bytes
os_getgroups_impl: 262184 bytes
Both function has local variable like this:
gid_t grouplist[MAX_GROUPS];
MAX_GROUPS is defined as:
```
#ifdef NGROUPS_MAX
#define MAX_GROUPS NGROUPS_MAX
#else
/* defined to be 16 on Solaris7, so this should be a small number */
#define MAX_GROUPS 64
#endif
```
NGROUPS_MAX is 65536 and sizeof(gid_t) is 4 on Ubuntu 20.04, so grouplist is
262144bytes.
It seems this grouplist is just for avoid allocation:
```
} else if (n <= MAX_GROUPS) {
/* groups will fit in existing array */
alt_grouplist = grouplist;
} else {
alt_grouplist = PyMem_New(gid_t, n);
if (alt_grouplist == NULL) {
return PyErr_NoMemory();
}
```
How about just using `#define MAX_GROUPS 64`?
Or should we remove this grouplist because os.grouplist() is not called so
frequently?
----------
components: Library (Lib)
messages: 412335
nosy: methane
priority: normal
severity: normal
status: open
title: Large C stack usage of os.getgroups() and os.setgroups()
versions: Python 3.11
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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue46606>
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