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Small cleanup/refactoring in support of PR #5213 (#5251)

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* Factor out detail/value_and_holder.h (from detail/type_caster_base.h)

This is in support of PR #5213:

* trampoline_self_life_support.h depends on value_and_holder.h

* type_caster_base.h depends on trampoline_self_life_support.h

* Fix a minor and inconsequential inconsistency in `copyable_holder_caster`: the correct `load_value()` return type is `void` (as defined in `type_caster_generic`)

For easy future reference, this is the long-standing inconsistency:

* dbf848aff7/include/pybind11/detail/type_caster_base.h (L634)

* dbf848aff7/include/pybind11/cast.h (L797)

Noticed in passing while working on PR #5213.

* Add `DANGER ZONE` comment in detail/init.h, similar to a comment added on the smart_holder branch (all the way back in 2021).
This commit is contained in:
Ralf W. Grosse-Kunstleve 2024-07-19 07:34:06 +07:00 committed by Henry Schreiner
parent f50830eae4
commit 129934ad9f
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GPG Key ID: B9D0E45146A241E8
6 changed files with 86 additions and 65 deletions
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1
CMakeLists.txt
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@ -154,6 +154,7 @@ set(PYBIND11_HEADERS
include/pybind11/detail/internals.h
include/pybind11/detail/type_caster_base.h
include/pybind11/detail/typeid.h
include/pybind11/detail/value_and_holder.h
include/pybind11/attr.h
include/pybind11/buffer_info.h
include/pybind11/cast.h

4
include/pybind11/cast.h
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@ -794,11 +794,11 @@ protected:
}
}
bool load_value(value_and_holder &&v_h) {
void load_value(value_and_holder &&v_h) {
if (v_h.holder_constructed()) {
value = v_h.value_ptr();
holder = v_h.template holder<holder_type>();
return true;
return;
}
throw cast_error("Unable to cast from non-held to held instance (T& to Holder<T>) "
#if !defined(PYBIND11_DETAILED_ERROR_MESSAGES)

4
include/pybind11/detail/init.h
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@ -128,11 +128,13 @@ void construct(value_and_holder &v_h, Cpp<Class> *ptr, bool need_alias) {
// the holder and destruction happens when we leave the C++ scope, and the holder
// class gets to handle the destruction however it likes.
v_h.value_ptr() = ptr;
v_h.set_instance_registered(true); // To prevent init_instance from registering it
v_h.set_instance_registered(true); // Trick to prevent init_instance from registering it
// DANGER ZONE BEGIN: exceptions will leave v_h in an invalid state.
v_h.type->init_instance(v_h.inst, nullptr); // Set up the holder
Holder<Class> temp_holder(std::move(v_h.holder<Holder<Class>>())); // Steal the holder
v_h.type->dealloc(v_h); // Destroys the moved-out holder remains, resets value ptr to null
v_h.set_instance_registered(false);
// DANGER ZONE END.
construct_alias_from_cpp<Class>(is_alias_constructible<Class>{}, v_h, std::move(*ptr));
} else {

62
include/pybind11/detail/type_caster_base.h
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@ -14,6 +14,7 @@
#include "descr.h"
#include "internals.h"
#include "typeid.h"
#include "value_and_holder.h"
#include <cstdint>
#include <iterator>
@ -259,67 +260,6 @@ PYBIND11_NOINLINE handle find_registered_python_instance(void *src,
});
}
struct value_and_holder {
instance *inst = nullptr;
size_t index = 0u;
const detail::type_info *type = nullptr;
void **vh = nullptr;
// Main constructor for a found value/holder:
value_and_holder(instance *i, const detail::type_info *type, size_t vpos, size_t index)
: inst{i}, index{index}, type{type},
vh{inst->simple_layout ? inst->simple_value_holder
: &inst->nonsimple.values_and_holders[vpos]} {}
// Default constructor (used to signal a value-and-holder not found by get_value_and_holder())
value_and_holder() = default;
// Used for past-the-end iterator
explicit value_and_holder(size_t index) : index{index} {}
template <typename V = void>
V *&value_ptr() const {
return reinterpret_cast<V *&>(vh[0]);
}
// True if this `value_and_holder` has a non-null value pointer
explicit operator bool() const { return value_ptr() != nullptr; }
template <typename H>
H &holder() const {
return reinterpret_cast<H &>(vh[1]);
}
bool holder_constructed() const {
return inst->simple_layout
? inst->simple_holder_constructed
: (inst->nonsimple.status[index] & instance::status_holder_constructed) != 0u;
}
// NOLINTNEXTLINE(readability-make-member-function-const)
void set_holder_constructed(bool v = true) {
if (inst->simple_layout) {
inst->simple_holder_constructed = v;
} else if (v) {
inst->nonsimple.status[index] |= instance::status_holder_constructed;
} else {
inst->nonsimple.status[index] &= (std::uint8_t) ~instance::status_holder_constructed;
}
}
bool instance_registered() const {
return inst->simple_layout
? inst->simple_instance_registered
: ((inst->nonsimple.status[index] & instance::status_instance_registered) != 0);
}
// NOLINTNEXTLINE(readability-make-member-function-const)
void set_instance_registered(bool v = true) {
if (inst->simple_layout) {
inst->simple_instance_registered = v;
} else if (v) {
inst->nonsimple.status[index] |= instance::status_instance_registered;
} else {
inst->nonsimple.status[index] &= (std::uint8_t) ~instance::status_instance_registered;
}
}
};
// Container for accessing and iterating over an instance's values/holders
struct values_and_holders {
private:

77
include/pybind11/detail/value_and_holder.h Normal file
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@ -0,0 +1,77 @@
// Copyright (c) 2016-2024 The Pybind Development Team.
// All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.
#pragma once
#include "common.h"
#include <cstddef>
#include <typeinfo>
PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
PYBIND11_NAMESPACE_BEGIN(detail)
struct value_and_holder {
instance *inst = nullptr;
size_t index = 0u;
const detail::type_info *type = nullptr;
void **vh = nullptr;
// Main constructor for a found value/holder:
value_and_holder(instance *i, const detail::type_info *type, size_t vpos, size_t index)
: inst{i}, index{index}, type{type},
vh{inst->simple_layout ? inst->simple_value_holder
: &inst->nonsimple.values_and_holders[vpos]} {}
// Default constructor (used to signal a value-and-holder not found by get_value_and_holder())
value_and_holder() = default;
// Used for past-the-end iterator
explicit value_and_holder(size_t index) : index{index} {}
template <typename V = void>
V *&value_ptr() const {
return reinterpret_cast<V *&>(vh[0]);
}
// True if this `value_and_holder` has a non-null value pointer
explicit operator bool() const { return value_ptr() != nullptr; }
template <typename H>
H &holder() const {
return reinterpret_cast<H &>(vh[1]);
}
bool holder_constructed() const {
return inst->simple_layout
? inst->simple_holder_constructed
: (inst->nonsimple.status[index] & instance::status_holder_constructed) != 0u;
}
// NOLINTNEXTLINE(readability-make-member-function-const)
void set_holder_constructed(bool v = true) {
if (inst->simple_layout) {
inst->simple_holder_constructed = v;
} else if (v) {
inst->nonsimple.status[index] |= instance::status_holder_constructed;
} else {
inst->nonsimple.status[index] &= (std::uint8_t) ~instance::status_holder_constructed;
}
}
bool instance_registered() const {
return inst->simple_layout
? inst->simple_instance_registered
: ((inst->nonsimple.status[index] & instance::status_instance_registered) != 0);
}
// NOLINTNEXTLINE(readability-make-member-function-const)
void set_instance_registered(bool v = true) {
if (inst->simple_layout) {
inst->simple_instance_registered = v;
} else if (v) {
inst->nonsimple.status[index] |= instance::status_instance_registered;
} else {
inst->nonsimple.status[index] &= (std::uint8_t) ~instance::status_instance_registered;
}
}
};
PYBIND11_NAMESPACE_END(detail)
PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)

1
tests/extra_python_package/test_files.py
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@ -58,6 +58,7 @@ detail_headers = {
"include/pybind11/detail/internals.h",
"include/pybind11/detail/type_caster_base.h",
"include/pybind11/detail/typeid.h",
"include/pybind11/detail/value_and_holder.h",
}
eigen_headers = {