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Use dynamic cast for shared_from_this holder init

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Using a dynamic_cast instead of a static_cast is needed to safely cast
from a base to a derived type.  The previous static_pointer_cast isn't
safe, however, when downcasting (and fails to compile when downcasting
with virtual inheritance).

Switching this to always use a dynamic_pointer_cast shouldn't incur any
additional overhead when a static_pointer_cast is safe (i.e. when
upcasting, or self-casting): compilers don't need RTTI checks in those
cases.
This commit is contained in:
Jason Rhinelander 2017-05-19 13:34:55 -04:00
parent 35998a0314
commit b8ac438386
3 changed files with 23 additions and 6 deletions
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12
include/pybind11/pybind11.h
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@ -1119,13 +1119,15 @@ private:
template <typename T> template <typename T>
static void init_holder_helper(instance_type *inst, const holder_type * /* unused */, const std::enable_shared_from_this<T> * /* dummy */) { static void init_holder_helper(instance_type *inst, const holder_type * /* unused */, const std::enable_shared_from_this<T> * /* dummy */) {
try { try {
new (&inst->holder) holder_type(std::static_pointer_cast<typename holder_type::element_type>(inst->value->shared_from_this())); auto sh = std::dynamic_pointer_cast<typename holder_type::element_type>(inst->value->shared_from_this());
inst->holder_constructed = true; if (sh) {
} catch (const std::bad_weak_ptr &) { new (&inst->holder) holder_type(std::move(sh));
if (inst->owned) {
new (&inst->holder) holder_type(inst->value);
inst->holder_constructed = true; inst->holder_constructed = true;
} }
} catch (const std::bad_weak_ptr &) {}
if (!inst->holder_constructed && inst->owned) {
new (&inst->holder) holder_type(inst->value);
inst->holder_constructed = true;
} }
} }

11
tests/test_smart_ptr.cpp
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@ -214,6 +214,12 @@ struct SharedFromThisRef {
std::shared_ptr<B> shared = std::make_shared<B>(); std::shared_ptr<B> shared = std::make_shared<B>();
}; };
// Issue #865: shared_from_this doesn't work with virtual inheritance
struct SharedFromThisVBase : std::enable_shared_from_this<SharedFromThisVBase> {
virtual ~SharedFromThisVBase() = default;
};
struct SharedFromThisVirt : virtual SharedFromThisVBase {};
template <typename T> template <typename T>
class CustomUniquePtr { class CustomUniquePtr {
std::unique_ptr<T> impl; std::unique_ptr<T> impl;
@ -258,6 +264,11 @@ test_initializer smart_ptr_and_references([](py::module &pm) {
.def("set_ref", [](SharedFromThisRef &, const B &) { return true; }) .def("set_ref", [](SharedFromThisRef &, const B &) { return true; })
.def("set_holder", [](SharedFromThisRef &, std::shared_ptr<B>) { return true; }); .def("set_holder", [](SharedFromThisRef &, std::shared_ptr<B>) { return true; });
// Issue #865: shared_from_this doesn't work with virtual inheritance
static std::shared_ptr<SharedFromThisVirt> sft(new SharedFromThisVirt());
py::class_<SharedFromThisVirt, std::shared_ptr<SharedFromThisVirt>>(m, "SharedFromThisVirt")
.def_static("get", []() { return sft.get(); });
struct C { struct C {
C() { print_created(this); } C() { print_created(this); }
~C() { print_destroyed(this); } ~C() { print_destroyed(this); }

6
tests/test_smart_ptr.py
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@ -166,7 +166,7 @@ def test_shared_ptr_and_references():
def test_shared_ptr_from_this_and_references(): def test_shared_ptr_from_this_and_references():
from pybind11_tests.smart_ptr import SharedFromThisRef, B from pybind11_tests.smart_ptr import SharedFromThisRef, B, SharedFromThisVirt
s = SharedFromThisRef() s = SharedFromThisRef()
stats = ConstructorStats.get(B) stats = ConstructorStats.get(B)
@ -202,6 +202,10 @@ def test_shared_ptr_from_this_and_references():
del ref, bad_wp, copy, holder_ref, holder_copy, s del ref, bad_wp, copy, holder_ref, holder_copy, s
assert stats.alive() == 0 assert stats.alive() == 0
z = SharedFromThisVirt.get()
y = SharedFromThisVirt.get()
assert y is z
def test_move_only_holder(): def test_move_only_holder():
from pybind11_tests.smart_ptr import TypeWithMoveOnlyHolder from pybind11_tests.smart_ptr import TypeWithMoveOnlyHolder