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gh-115432: Add critical section variant that handles a NULL object #115433

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merged 4 commits into from
Feb 15, 2024
Merged

gh-115432: Add critical section variant that handles a NULL object #115433

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7b4e4e7
gh-115432: Add critical section variant that handles a NULL object
colesbury Feb 13, 2024
54491d7
Avoid warning in default build
colesbury Feb 13, 2024
f6ba3b9
Use 'X' prefix for consistency with Py_XDECREF, Py_XNewRef, etc.
colesbury Feb 14, 2024
59a8b74
Fix definition for default build
colesbury Feb 14, 2024
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29 changes: 29 additions & 0 deletions Include/internal/pycore_critical_section.h
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Original file line number Diff line number Diff line change
Expand Up @@ -96,6 +96,15 @@ extern "C" {
_PyCriticalSection_End(&_cs); \
}

# define Py_XBEGIN_CRITICAL_SECTION(op) \
{ \
_PyCriticalSection _cs_opt = {0}; \
_PyCriticalSection_XBegin(&_cs_opt, _PyObject_CAST(op))

# define Py_XEND_CRITICAL_SECTION() \
_PyCriticalSection_XEnd(&_cs_opt); \
}

# define Py_BEGIN_CRITICAL_SECTION2(a, b) \
{ \
_PyCriticalSection2 _cs2; \
Expand Down Expand Up @@ -131,6 +140,8 @@ extern "C" {
// The critical section APIs are no-ops with the GIL.
# define Py_BEGIN_CRITICAL_SECTION(op)
# define Py_END_CRITICAL_SECTION()
# define Py_XBEGIN_CRITICAL_SECTION(op)
# define Py_XEND_CRITICAL_SECTION()
# define Py_BEGIN_CRITICAL_SECTION2(a, b)
# define Py_END_CRITICAL_SECTION2()
# define _Py_CRITICAL_SECTION_ASSERT_MUTEX_LOCKED(mutex)
Expand Down Expand Up @@ -187,6 +198,16 @@ _PyCriticalSection_Begin(_PyCriticalSection *c, PyMutex *m)
}
}

static inline void
_PyCriticalSection_XBegin(_PyCriticalSection *c, PyObject *op)
{
#ifdef Py_GIL_DISABLED
if (op != NULL) {
_PyCriticalSection_Begin(c, &_PyObject_CAST(op)->ob_mutex);
}
#endif
Comment on lines +204 to +208
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Is the #ifdef needed here? The whole macro should be a no-op when the GIL is enabled

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It's needed because of the &_PyObject_CAST(op)->ob_mutex will only compile on the free-threaded build. In the default build, PyObject does not have an ob_mutex field.

We could have instead put the #ifdef Py_GIL_DISABLED around the whole _PyCriticalSection_BeginOpt function declaration. That would work too.

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Ah cool, thanks for clearing that up!

}

// Removes the top-most critical section from the thread's stack of critical
// sections. If the new top-most critical section is inactive, then it is
// resumed.
Expand All @@ -209,6 +230,14 @@ _PyCriticalSection_End(_PyCriticalSection *c)
_PyCriticalSection_Pop(c);
}

static inline void
_PyCriticalSection_XEnd(_PyCriticalSection *c)
{
if (c->mutex) {
_PyCriticalSection_End(c);
}
}

static inline void
_PyCriticalSection2_Begin(_PyCriticalSection2 *c, PyMutex *m1, PyMutex *m2)
{
Expand Down
9 changes: 9 additions & 0 deletions Modules/_testinternalcapi/test_critical_sections.c
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Expand Up @@ -49,6 +49,15 @@ test_critical_sections(PyObject *self, PyObject *Py_UNUSED(args))
Py_END_CRITICAL_SECTION2();
assert_nogil(!PyMutex_IsLocked(&d2->ob_mutex));

// Optional variant behaves the same if the object is non-NULL
Py_XBEGIN_CRITICAL_SECTION(d1);
assert_nogil(PyMutex_IsLocked(&d1->ob_mutex));
Py_XEND_CRITICAL_SECTION();

// No-op
Py_XBEGIN_CRITICAL_SECTION(NULL);
Py_XEND_CRITICAL_SECTION();

Py_DECREF(d2);
Py_DECREF(d1);
Py_RETURN_NONE;
Expand Down
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