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gh-150902: Optimize PyCriticalSection2 to skip locking the same locks as the ones held by the current CS2 #151085

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gh-150902: Optimize PyCriticalSection2 to skip locking the same locks as the ones held by the current CS2 #151085

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gh-150902: Optimize `PyCriticalSection2` to skip locking the same loc…
dpdani Jun 8, 2026
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📜🤖 Added by blurb_it.
blurb-it[bot] Jun 8, 2026
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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2026-06-08-13-14-42.gh-issue-150902.-CWZ66.rst
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@@ -0,0 +1 @@
Apply an existing optimization of PyCriticalSection (single mutex) to PyCriticalSection2: avoid acquiring the same locks that the current CS has already acquired.
15 changes: 15 additions & 0 deletions Python/critical_section.c
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Expand Up @@ -72,6 +72,21 @@ _PyCriticalSection2_BeginSlow(PyThreadState *tstate, PyCriticalSection2 *c, PyMu
c->_cs_base._cs_prev = 0;
return;
}
// Same optimization as in _PyCriticalSection_BeginSlow: skip locking when
// recursively acquiring the same locks.
if (tstate->critical_section &&
tstate->critical_section & _Py_CRITICAL_SECTION_TWO_MUTEXES) {
PyCriticalSection2 *prev2 = (PyCriticalSection2 *)
untag_critical_section(tstate->critical_section);
assert(m1 < m2);
assert(prev2->_cs_base._cs_mutex < prev2->_cs_mutex2);
if (prev2->_cs_base._cs_mutex == m1 && prev2->_cs_mutex2 == m2) {
c->_cs_base._cs_mutex = NULL;
c->_cs_mutex2 = NULL;
c->_cs_base._cs_prev = 0;
return;
}
}
c->_cs_base._cs_mutex = NULL;
c->_cs_mutex2 = NULL;
c->_cs_base._cs_prev = tstate->critical_section;
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