From 8802d23ba9c07d32d0da22213d8e76ed102d553f Mon Sep 17 00:00:00 2001
From: =?utf8?q?J=C3=A9r=C3=A9mie=20Galarneau?=
 <jeremie.galarneau@efficios.com>
Date: Thu, 28 Apr 2022 11:28:15 -0400
Subject: [PATCH] Add make_unique_wrapper()
MIME-Version: 1.0
Content-Type: text/plain; charset=utf8
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make_unique_wrapper is intended to facilitate the use of std::unique_ptr
to wrap C-style APIs that don't provide RAII resource management facilities.

Usage example:

   // API
   struct my_c_struct {
           // ...
   };

   struct my_c_struct *create_my_c_struct(void);
   void destroy_my_c_struct(struct my_c_struct *value);

   // Creating a unique_ptr to my_c_struct.
   auto safe_c_struct =
           lttng::make_unique_wrapper<my_c_struct, destroy_my_c_struct>(
                   create_my_c_struct());

Note that this facility is intended for use in the scope of a function.
If you need to return this unique_ptr instance, you should consider writting
a proper, idiomatic, wrapper.

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Change-Id: I429fc6f62896efb04af95fc26143096043206265
---
 src/common/Makefile.am             |  1 +
 src/common/make-unique-wrapper.hpp | 82 ++++++++++++++++++++++++++++++
 2 files changed, 83 insertions(+)
 create mode 100644 src/common/make-unique-wrapper.hpp

diff --git a/src/common/Makefile.am b/src/common/Makefile.am
index b0191dd47..928f8d30b 100644
--- a/src/common/Makefile.am
+++ b/src/common/Makefile.am
@@ -87,6 +87,7 @@ libcommon_lgpl_la_SOURCES = \
 	kernel-probe.cpp \
 	location.cpp \
 	log-level-rule.cpp \
+	make-unique-wrapper.hpp \
 	mi-lttng.cpp mi-lttng.hpp \
 	notification.cpp \
 	payload.cpp payload.hpp \
diff --git a/src/common/make-unique-wrapper.hpp b/src/common/make-unique-wrapper.hpp
new file mode 100644
index 000000000..50d1916f2
--- /dev/null
+++ b/src/common/make-unique-wrapper.hpp
@@ -0,0 +1,82 @@
+/*
+ * Copyright (C) 2022 Jérémie Galarneau <jeremie.galarneau@efficios.com>
+ *
+ * SPDX-License-Identifier: LGPL-2.1-only
+ *
+ */
+
+#ifndef LTTNG_MAKE_UNIQUE_WRAPPER_H
+#define LTTNG_MAKE_UNIQUE_WRAPPER_H
+
+#include <common/macros.hpp>
+
+#include <memory>
+
+namespace lttng {
+
+/*
+ * make_unique_wrapper is intended to facilitate the use of std::unique_ptr
+ * to wrap C-style APIs that don't provide RAII resource management facilities.
+ *
+ * Usage example:
+ *
+ *    // API
+ *    struct my_c_struct {
+ *            // ...
+ *    };
+ *
+ *    struct my_c_struct *create_my_c_struct(void);
+ *    void destroy_my_c_struct(struct my_c_struct *value);
+ *
+ *    // Creating a unique_ptr to my_c_struct.
+ *    auto safe_c_struct =
+ *            lttng::make_unique_wrapper<my_c_struct, destroy_my_c_struct>(
+ *                    create_my_c_struct());
+ *
+ * Note that this facility is intended for use in the scope of a function.
+ * If you need to return this unique_ptr instance, you should consider writting
+ * a proper, idiomatic, wrapper.
+ */
+
+namespace details
+{
+template <typename WrappedType, void (*DeleterFunction)(WrappedType *)>
+struct create_unique_class {
+	struct deleter {
+		void operator()(WrappedType *instance) const
+		{
+			DeleterFunction(instance);
+		}
+	};
+
+	std::unique_ptr<WrappedType, deleter> operator()(WrappedType *instance) const
+	{
+		return std::unique_ptr<WrappedType, deleter>(instance);
+	}
+};
+} /* namespace details */
+
+/*
+ * 'free' is a utility function for use with make_unique_wrapper. It makes it easier to
+ * wrap raw pointers that have to be deleted with `free`. Using libc's 'free' as
+ * a make_unique_wrapper template argument will result in an error as 'WrappedType *' will
+ * not match free's 'void *' argument.
+ */
+template <class Type>
+void free(Type *ptr)
+{
+	std::free(ptr);
+}
+
+template <typename WrappedType, void (*DeleterFunc)(WrappedType *)>
+std::unique_ptr<WrappedType, typename details::create_unique_class<WrappedType, DeleterFunc>::deleter>
+make_unique_wrapper(WrappedType *instance)
+{
+	const details::create_unique_class<WrappedType, DeleterFunc> unique_deleter;
+
+	return unique_deleter(instance);
+}
+
+} /* namespace lttng */
+
+#endif /* LTTNG_MAKE_UNIQUE_WRAPPER_H */
-- 
2.34.1