From 4f00ffdc69482daa6c0a253ad5ee820cccf0bfb7 Mon Sep 17 00:00:00 2001
From: "Ralf W. Grosse-Kunstleve" <rwgk@google.com>
Date: Thu, 10 Jun 2021 07:17:32 -0700
Subject: [PATCH] Copying in shared_from_this_custom_deleters.cpp from
 github.com/rwgk, with adjustments.

Base version: https://github.com/rwgk/stuff/blob/e5318faa6a8583b7c338e01398a4eea69abda08d/shared_from_this_custom_deleters.cpp
---
 tests/test_class_sh_shared_from_this.cpp | 98 ++++++++++++++++++++++++
 tests/test_class_sh_shared_from_this.py  | 12 +++
 2 files changed, 110 insertions(+)

diff --git a/tests/test_class_sh_shared_from_this.cpp b/tests/test_class_sh_shared_from_this.cpp
index b81d1fae5..b210ba27e 100644
--- a/tests/test_class_sh_shared_from_this.cpp
+++ b/tests/test_class_sh_shared_from_this.cpp
@@ -1,10 +1,98 @@
 #include "pybind11_tests.h"
+
 #include "object.h"
 
 #include <pybind11/smart_holder.h>
 
+#include <iostream>
+#include <stdexcept>
+
+namespace shared_from_this_custom_deleters {
+
+template <typename T>
+struct labeled_delete {
+    std::string label;
+    explicit labeled_delete(const std::string &label) : label{label} {}
+    void operator()(T *raw_ptr) {
+        std::cout << "labeled_delete::operator() " << label << std::endl;
+        if (label != "SkipDelete") {
+            delete raw_ptr;
+        }
+    }
+};
+
+struct Atype : std::enable_shared_from_this<Atype> {};
+
+#define SHOW_USE_COUNTS                                                                           \
+    std::cout << "obj1, obj2 use_counts: " << obj1.use_count() << ", " << obj2.use_count()        \
+              << std::endl;
+
+void obj1_owns() {
+    std::cout << "\nobj1_owns()" << std::endl;
+    std::shared_ptr<Atype> obj1(new Atype, labeled_delete<Atype>("1st"));
+    std::shared_ptr<Atype> obj2(obj1.get(), labeled_delete<Atype>("SkipDelete"));
+    SHOW_USE_COUNTS
+    auto sft1 = obj1->shared_from_this();
+    SHOW_USE_COUNTS
+    auto sft2 = obj2->shared_from_this();
+    SHOW_USE_COUNTS
+}
+
+void obj2_owns() {
+    std::cout << "\nobj2_owns()" << std::endl;
+    std::shared_ptr<Atype> obj1(new Atype, labeled_delete<Atype>("SkipDelete"));
+    std::shared_ptr<Atype> obj2(obj1.get(), labeled_delete<Atype>("2nd"));
+    SHOW_USE_COUNTS
+    auto sft1 = obj1->shared_from_this();
+    SHOW_USE_COUNTS
+    auto sft2 = obj2->shared_from_this();
+    SHOW_USE_COUNTS
+}
+
+void obj_sft_reset() {
+    std::cout << "\nobj_sft_reset()" << std::endl;
+    std::shared_ptr<Atype> obj1(new Atype, labeled_delete<Atype>("SkipDelete"));
+    std::shared_ptr<Atype> obj2(obj1.get(), labeled_delete<Atype>("ThisDeletes"));
+    std::shared_ptr<Atype> *obj_sft = nullptr;
+    std::shared_ptr<Atype> *obj_ign = nullptr;
+    {
+        auto sft1 = obj1->shared_from_this();
+        auto sft2 = obj2->shared_from_this();
+        long uc1  = obj1.use_count();
+        long uc2  = obj2.use_count();
+        if (uc1 == 3 && uc2 == 1) {
+            std::cout << "SHARED_FROM_THIS_REFERENT: 1" << std::endl;
+            obj_sft = &obj1;
+            obj_ign = &obj2;
+        } else if (uc1 == 1 && uc2 == 3) {
+            std::cout << "SHARED_FROM_THIS_REFERENT: 2" << std::endl;
+            obj_sft = &obj2;
+            obj_ign = &obj1;
+        } else {
+            std::cout << "SHARED_FROM_THIS_REFERENT: UNKNOWN" << std::endl;
+        }
+    }
+    if (obj_sft == nullptr)
+        throw std::runtime_error("Unexpected `use_count`s.");
+    (*obj_sft).reset();
+    bool got_bad_weak_ptr = false;
+    try {
+        (*obj_ign)->shared_from_this();
+    } catch (const std::bad_weak_ptr &) {
+        got_bad_weak_ptr = true;
+    }
+    std::cout << "got_bad_weak_ptr: " << got_bad_weak_ptr << std::endl;
+    std::shared_ptr<Atype> obj3(obj2.get(), labeled_delete<Atype>("SkipDelete"));
+    // Working again based on the shared_ptr that was created after obj_sft was reset:
+    (*obj_ign)->shared_from_this();
+}
+
+} // namespace shared_from_this_custom_deleters
+
 namespace test_class_sh_shared_from_this {
 
+// clang-format off
+
 class MyObject3 : public std::enable_shared_from_this<MyObject3> {
 public:
     MyObject3(const MyObject3 &) = default;
@@ -35,6 +123,8 @@ struct SharedFromThisVBase : std::enable_shared_from_this<SharedFromThisVBase> {
 
 struct SharedFromThisVirt : virtual SharedFromThisVBase {};
 
+// clang-format on
+
 } // namespace test_class_sh_shared_from_this
 
 using namespace test_class_sh_shared_from_this;
@@ -45,6 +135,8 @@ PYBIND11_SMART_HOLDER_TYPE_CASTERS(SharedFromThisRef)
 PYBIND11_SMART_HOLDER_TYPE_CASTERS(SharedFromThisVirt)
 
 TEST_SUBMODULE(class_sh_shared_from_this, m) {
+    // clang-format off
+
     py::classh<MyObject3>(m, "MyObject3")
         .def(py::init<int>());
     m.def("make_myobject3_1", []() { return new MyObject3(8); });
@@ -71,4 +163,10 @@ TEST_SUBMODULE(class_sh_shared_from_this, m) {
     static std::shared_ptr<SharedFromThisVirt> sft(new SharedFromThisVirt());
     py::classh<SharedFromThisVirt>(m, "SharedFromThisVirt")
         .def_static("get", []() { return sft.get(); }, py::return_value_policy::reference);
+
+    // clang-format on
+
+    m.def("obj1_owns", shared_from_this_custom_deleters::obj1_owns);
+    m.def("obj2_owns", shared_from_this_custom_deleters::obj2_owns);
+    m.def("obj_sft_reset", shared_from_this_custom_deleters::obj_sft_reset);
 }
diff --git a/tests/test_class_sh_shared_from_this.py b/tests/test_class_sh_shared_from_this.py
index 5dd0234d4..26501bf68 100644
--- a/tests/test_class_sh_shared_from_this.py
+++ b/tests/test_class_sh_shared_from_this.py
@@ -109,3 +109,15 @@ def test_shared_from_this_virt():
     z = m.SharedFromThisVirt.get()
     y = m.SharedFromThisVirt.get()
     assert y is z
+
+
+@pytest.mark.parametrize(
+    "test_func",
+    [
+        m.obj1_owns,
+        m.obj2_owns,
+        m.obj_sft_reset,
+    ],
+)
+def test_shared_from_this_custom_deleters(test_func):
+    test_func()