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Implement reference_internal with a keep_alive
reference_internal requires an `instance` field to track the returned reference's parent, but that's just a duplication of what keep_alive<0,1> does, so use a keep alive to do this to eliminate the duplication.
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@ -612,17 +612,11 @@ functions. The default policy is :enum:`return_value_policy::automatic`.
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| | it is no longer used. Warning: undefined behavior will ensue when the C++ |
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| | it is no longer used. Warning: undefined behavior will ensue when the C++ |
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| | side deletes an object that is still referenced and used by Python. |
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| | side deletes an object that is still referenced and used by Python. |
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+--------------------------------------------------+----------------------------------------------------------------------------+
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+--------------------------------------------------+----------------------------------------------------------------------------+
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| :enum:`return_value_policy::reference_internal` | This policy only applies to methods and properties. It references the |
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| :enum:`return_value_policy::reference_internal` | Like :enum:`return_value_policy::reference` but additionally applies a |
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| | object without taking ownership similar to the above |
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| | :class:`keep_alive<0,1>()` call policy (described next) that keeps the |
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| | :enum:`return_value_policy::reference` policy. In contrast to that policy, |
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| | ``this`` argument of the function or property from being garbage collected |
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| | the function or property's implicit ``this`` argument (called the *parent*)|
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| | as long as the return value remains referenced. See the |
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| | is considered to be the the owner of the return value (the *child*). |
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| | :class:`keep_alive` call policy (described next) for details. |
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| | pybind11 then couples the lifetime of the parent to the child via a |
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| | reference relationship that ensures that the parent cannot be garbage |
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| | collected while Python is still using the child. More advanced variations |
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| | of this scheme are also possible using combinations of |
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| | :enum:`return_value_policy::reference` and the :class:`keep_alive` call |
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| | policy described next. |
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+--------------------------------------------------+----------------------------------------------------------------------------+
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+--------------------------------------------------+----------------------------------------------------------------------------+
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.. warning::
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.. warning::
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@ -161,10 +161,13 @@ void init_issues(py::module &m) {
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// Issue #328: first member in a class can't be used in operators
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// Issue #328: first member in a class can't be used in operators
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#define TRACKERS(CLASS) CLASS() { std::cout << #CLASS "@" << this << " constructor\n"; } \
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#define TRACKERS(CLASS) CLASS() { std::cout << #CLASS "@" << this << " constructor\n"; } \
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~CLASS() { std::cout << #CLASS "@" << this << " destructor\n"; }
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~CLASS() { std::cout << #CLASS "@" << this << " destructor\n"; }
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struct NestA { int value = 3; NestA& operator+=(int i) { value += i; return *this; } TRACKERS(NestA) };
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struct NestABase { int value = -2; TRACKERS(NestABase) };
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struct NestA : NestABase { int value = 3; NestA& operator+=(int i) { value += i; return *this; } TRACKERS(NestA) };
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struct NestB { NestA a; int value = 4; NestB& operator-=(int i) { value -= i; return *this; } TRACKERS(NestB) };
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struct NestB { NestA a; int value = 4; NestB& operator-=(int i) { value -= i; return *this; } TRACKERS(NestB) };
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struct NestC { NestB b; int value = 5; NestC& operator*=(int i) { value *= i; return *this; } TRACKERS(NestC) };
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struct NestC { NestB b; int value = 5; NestC& operator*=(int i) { value *= i; return *this; } TRACKERS(NestC) };
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py::class_<NestA>(m2, "NestA").def(py::init<>()).def(py::self += int());
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py::class_<NestABase>(m2, "NestABase").def(py::init<>()).def_readwrite("value", &NestABase::value);
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py::class_<NestA>(m2, "NestA").def(py::init<>()).def(py::self += int())
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.def("as_base", [](NestA &a) -> NestABase& { return (NestABase&) a; }, py::return_value_policy::reference_internal);
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py::class_<NestB>(m2, "NestB").def(py::init<>()).def(py::self -= int()).def_readwrite("a", &NestB::a);
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py::class_<NestB>(m2, "NestB").def(py::init<>()).def(py::self -= int()).def_readwrite("a", &NestB::a);
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py::class_<NestC>(m2, "NestC").def(py::init<>()).def(py::self *= int()).def_readwrite("b", &NestC::b);
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py::class_<NestC>(m2, "NestC").def(py::init<>()).def(py::self *= int()).def_readwrite("b", &NestC::b);
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m2.def("print_NestA", [](const NestA &a) { std::cout << a.value << std::endl; });
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m2.def("print_NestA", [](const NestA &a) { std::cout << a.value << std::endl; });
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@ -95,3 +95,17 @@ print_NestA(c.b.a)
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print_NestB(b)
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print_NestB(b)
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print_NestB(c.b)
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print_NestB(c.b)
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print_NestC(c)
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print_NestC(c)
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abase = a.as_base()
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print(abase.value)
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a.as_base().value += 44
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print(abase.value)
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print(c.b.a.as_base().value)
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c.b.a.as_base().value += 44
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print(c.b.a.as_base().value)
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del c
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gc.collect()
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del a # Should't delete while abase is still alive
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gc.collect()
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print(abase.value)
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del abase
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gc.collect()
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@ -24,9 +24,12 @@ Failed as expected: Incompatible constructor arguments. The following argument t
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1. example.issues.StrIssue(arg0: int)
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1. example.issues.StrIssue(arg0: int)
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2. example.issues.StrIssue()
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2. example.issues.StrIssue()
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Invoked with: no, such, constructor
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Invoked with: no, such, constructor
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NestABase@0x1152940 constructor
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NestA@0x1152940 constructor
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NestA@0x1152940 constructor
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NestABase@0x11f9350 constructor
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NestA@0x11f9350 constructor
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NestA@0x11f9350 constructor
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NestB@0x11f9350 constructor
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NestB@0x11f9350 constructor
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NestABase@0x112d0d0 constructor
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NestA@0x112d0d0 constructor
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NestA@0x112d0d0 constructor
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NestB@0x112d0d0 constructor
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NestB@0x112d0d0 constructor
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NestC@0x112d0d0 constructor
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NestC@0x112d0d0 constructor
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@ -36,9 +39,17 @@ NestC@0x112d0d0 constructor
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3
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3
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1
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1
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35
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35
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-2
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42
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-2
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42
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NestC@0x112d0d0 destructor
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NestC@0x112d0d0 destructor
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NestB@0x112d0d0 destructor
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NestB@0x112d0d0 destructor
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NestA@0x112d0d0 destructor
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NestA@0x112d0d0 destructor
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NestABase@0x112d0d0 destructor
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42
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NestA@0x1152940 destructor
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NestABase@0x1152940 destructor
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NestB@0x11f9350 destructor
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NestB@0x11f9350 destructor
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NestA@0x11f9350 destructor
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NestA@0x11f9350 destructor
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NestA@0x1152940 destructor
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NestABase@0x11f9350 destructor
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@ -142,6 +142,9 @@ inline PyThreadState *get_thread_state_unchecked() {
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#endif
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#endif
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}
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}
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// Forward declaration
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inline void keep_alive_impl(handle nurse, handle patient);
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class type_caster_generic {
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class type_caster_generic {
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public:
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public:
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PYBIND11_NOINLINE type_caster_generic(const std::type_info &type_info)
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PYBIND11_NOINLINE type_caster_generic(const std::type_info &type_info)
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@ -208,7 +211,6 @@ public:
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wrapper->value = src;
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wrapper->value = src;
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wrapper->owned = true;
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wrapper->owned = true;
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wrapper->parent = nullptr;
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if (policy == return_value_policy::automatic)
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if (policy == return_value_policy::automatic)
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policy = return_value_policy::take_ownership;
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policy = return_value_policy::take_ownership;
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@ -229,7 +231,7 @@ public:
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wrapper->owned = false;
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wrapper->owned = false;
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} else if (policy == return_value_policy::reference_internal) {
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} else if (policy == return_value_policy::reference_internal) {
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wrapper->owned = false;
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wrapper->owned = false;
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wrapper->parent = parent.inc_ref().ptr();
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detail::keep_alive_impl(inst, parent);
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}
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}
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tinfo->init_holder(inst.ptr(), existing_holder);
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tinfo->init_holder(inst.ptr(), existing_holder);
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@ -245,7 +245,6 @@ inline std::string error_string();
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template <typename type> struct instance_essentials {
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template <typename type> struct instance_essentials {
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PyObject_HEAD
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PyObject_HEAD
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type *value;
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type *value;
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PyObject *parent;
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PyObject *weakrefs;
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PyObject *weakrefs;
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bool owned : 1;
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bool owned : 1;
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bool constructed : 1;
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bool constructed : 1;
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@ -729,7 +729,6 @@ protected:
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auto tinfo = detail::get_type_info(type);
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auto tinfo = detail::get_type_info(type);
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self->value = ::operator new(tinfo->type_size);
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self->value = ::operator new(tinfo->type_size);
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self->owned = true;
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self->owned = true;
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self->parent = nullptr;
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self->constructed = false;
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self->constructed = false;
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detail::get_internals().registered_instances.emplace(self->value, (PyObject *) self);
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detail::get_internals().registered_instances.emplace(self->value, (PyObject *) self);
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return (PyObject *) self;
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return (PyObject *) self;
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@ -751,7 +750,6 @@ protected:
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if (!found)
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if (!found)
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pybind11_fail("generic_type::dealloc(): Tried to deallocate unregistered instance!");
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pybind11_fail("generic_type::dealloc(): Tried to deallocate unregistered instance!");
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Py_XDECREF(self->parent);
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if (self->weakrefs)
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if (self->weakrefs)
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PyObject_ClearWeakRefs((PyObject *) self);
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PyObject_ClearWeakRefs((PyObject *) self);
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}
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}
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@ -1095,11 +1093,8 @@ template <typename... Args> struct init {
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}
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}
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};
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};
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PYBIND11_NOINLINE inline void keep_alive_impl(int Nurse, int Patient, handle args, handle ret) {
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inline void keep_alive_impl(handle nurse, handle patient) {
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/* Clever approach based on weak references taken from Boost.Python */
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/* Clever approach based on weak references taken from Boost.Python */
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handle nurse (Nurse > 0 ? PyTuple_GetItem(args.ptr(), Nurse - 1) : ret.ptr());
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handle patient(Patient > 0 ? PyTuple_GetItem(args.ptr(), Patient - 1) : ret.ptr());
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if (!nurse || !patient)
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if (!nurse || !patient)
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pybind11_fail("Could not activate keep_alive!");
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pybind11_fail("Could not activate keep_alive!");
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@ -1115,6 +1110,13 @@ PYBIND11_NOINLINE inline void keep_alive_impl(int Nurse, int Patient, handle arg
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(void) wr.release();
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(void) wr.release();
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}
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}
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PYBIND11_NOINLINE inline void keep_alive_impl(int Nurse, int Patient, handle args, handle ret) {
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handle nurse (Nurse > 0 ? PyTuple_GetItem(args.ptr(), Nurse - 1) : ret.ptr());
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handle patient(Patient > 0 ? PyTuple_GetItem(args.ptr(), Patient - 1) : ret.ptr());
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keep_alive_impl(nurse, patient);
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}
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template <typename Iterator> struct iterator_state {
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template <typename Iterator> struct iterator_state {
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Iterator it, end;
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Iterator it, end;
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bool first;
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bool first;
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