--- /dev/null
+/*
+ * This file is open source software, licensed to you under the terms
+ * of the Apache License, Version 2.0 (the "License"). See the NOTICE file
+ * distributed with this work for additional information regarding copyright
+ * ownership. You may not use this file except in compliance with the License.
+ *
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+/*
+ * Copyright (C) 2014 Cloudius Systems, Ltd.
+ */
+
+#ifndef CEPH_COMMON_DELETER_H
+#define CEPH_COMMON_DELETER_H
+
+#include <atomic>
+#include <memory>
+#include <cstdlib>
+#include <type_traits>
+
+#include "include/assert.h"
+
+/// \addtogroup memory-module
+/// @{
+
+/// Provides a mechanism for managing the lifetime of a buffer.
+///
+/// A \c deleter is an object that is used to inform the consumer
+/// of some buffer (not referenced by the deleter itself) how to
+/// delete the buffer. This can be by calling an arbitrary function
+/// or destroying an object carried by the deleter. Examples of
+/// a deleter's encapsulated actions are:
+///
+/// - calling \c std::free(p) on some captured pointer, p
+/// - calling \c delete \c p on some captured pointer, p
+/// - decrementing a reference count somewhere
+///
+/// A deleter performs its action from its destructor.
+class deleter final {
+ public:
+ /// \cond internal
+ struct impl;
+ struct raw_object_tag {};
+ /// \endcond
+ private:
+ // if bit 0 set, point to object to be freed directly.
+ impl* _impl = nullptr;
+ public:
+ /// Constructs an empty deleter that does nothing in its destructor.
+ deleter() = default;
+ deleter(const deleter&) = delete;
+ /// Moves a deleter.
+ deleter(deleter&& x) noexcept : _impl(x._impl) { x._impl = nullptr; }
+ /// \cond internal
+ explicit deleter(impl* i) : _impl(i) {}
+ deleter(raw_object_tag tag, void* object)
+ : _impl(from_raw_object(object)) {}
+ /// \endcond
+ /// Destroys the deleter and carries out the encapsulated action.
+ ~deleter();
+ deleter& operator=(deleter&& x);
+ deleter& operator=(deleter&) = delete;
+ /// Performs a sharing operation. The encapsulated action will only
+ /// be carried out after both the original deleter and the returned
+ /// deleter are both destroyed.
+ ///
+ /// \return a deleter with the same encapsulated action as this one.
+ deleter share();
+ /// Checks whether the deleter has an associated action.
+ explicit operator bool() const { return bool(_impl); }
+ /// \cond internal
+ void reset(impl* i) {
+ this->~deleter();
+ new (this) deleter(i);
+ }
+ /// \endcond
+ /// Appends another deleter to this deleter. When this deleter is
+ /// destroyed, both encapsulated actions will be carried out.
+ void append(deleter d);
+ private:
+ static bool is_raw_object(impl* i) {
+ auto x = reinterpret_cast<uintptr_t>(i);
+ return x & 1;
+ }
+ bool is_raw_object() const {
+ return is_raw_object(_impl);
+ }
+ static void* to_raw_object(impl* i) {
+ auto x = reinterpret_cast<uintptr_t>(i);
+ return reinterpret_cast<void*>(x & ~uintptr_t(1));
+ }
+ void* to_raw_object() const {
+ return to_raw_object(_impl);
+ }
+ impl* from_raw_object(void* object) {
+ auto x = reinterpret_cast<uintptr_t>(object);
+ return reinterpret_cast<impl*>(x | 1);
+ }
+};
+
+/// \cond internal
+struct deleter::impl {
+ std::atomic_uint refs;
+ deleter next;
+ impl(deleter next) : refs(1), next(std::move(next)) {}
+ virtual ~impl() {}
+};
+/// \endcond
+
+inline deleter::~deleter() {
+ if (is_raw_object()) {
+ std::free(to_raw_object());
+ return;
+ }
+ if (_impl && --_impl->refs == 0) {
+ delete _impl;
+ }
+}
+
+inline deleter& deleter::operator=(deleter&& x) {
+ if (this != &x) {
+ this->~deleter();
+ new (this) deleter(std::move(x));
+ }
+ return *this;
+}
+
+/// \cond internal
+template <typename Deleter>
+struct lambda_deleter_impl final : deleter::impl {
+ Deleter del;
+ lambda_deleter_impl(deleter next, Deleter&& del)
+ : impl(std::move(next)), del(std::move(del)) {}
+ virtual ~lambda_deleter_impl() override { del(); }
+};
+
+template <typename Object>
+struct object_deleter_impl final : deleter::impl {
+ Object obj;
+ object_deleter_impl(deleter next, Object&& obj)
+ : impl(std::move(next)), obj(std::move(obj)) {}
+};
+
+template <typename Object>
+inline
+object_deleter_impl<Object>* make_object_deleter_impl(deleter next, Object obj) {
+ return new object_deleter_impl<Object>(std::move(next), std::move(obj));
+}
+/// \endcond
+
+/// Makes a \ref deleter that encapsulates the action of
+/// destroying an object, as well as running another deleter. The input
+/// object is moved to the deleter, and destroyed when the deleter is destroyed.
+///
+/// \param d deleter that will become part of the new deleter's encapsulated action
+/// \param o object whose destructor becomes part of the new deleter's encapsulated action
+/// \related deleter
+template <typename Object>
+deleter make_deleter(deleter next, Object o) {
+ return deleter(new lambda_deleter_impl<Object>(std::move(next), std::move(o)));
+}
+
+/// Makes a \ref deleter that encapsulates the action of destroying an object. The input
+/// object is moved to the deleter, and destroyed when the deleter is destroyed.
+///
+/// \param o object whose destructor becomes the new deleter's encapsulated action
+/// \related deleter
+template <typename Object>
+deleter make_deleter(Object o) {
+ return make_deleter(deleter(), std::move(o));
+}
+
+/// \cond internal
+struct free_deleter_impl final : deleter::impl {
+ void* obj;
+ free_deleter_impl(void* obj) : impl(deleter()), obj(obj) {}
+ virtual ~free_deleter_impl() override { std::free(obj); }
+};
+/// \endcond
+
+inline deleter deleter::share() {
+ if (!_impl) {
+ return deleter();
+ }
+ if (is_raw_object()) {
+ _impl = new free_deleter_impl(to_raw_object());
+ }
+ ++_impl->refs;
+ return deleter(_impl);
+}
+
+// Appends 'd' to the chain of deleters. Avoids allocation if possible. For
+// performance reasons the current chain should be shorter and 'd' should be
+// longer.
+inline void deleter::append(deleter d) {
+ if (!d._impl) {
+ return;
+ }
+ impl* next_impl = _impl;
+ deleter* next_d = this;
+ while (next_impl) {
+ if (next_impl == d._impl)
+ return ;
+ if (is_raw_object(next_impl)) {
+ next_d->_impl = next_impl = new free_deleter_impl(to_raw_object(next_impl));
+ }
+ if (next_impl->refs != 1) {
+ next_d->_impl = next_impl = make_object_deleter_impl(std::move(next_impl->next), deleter(next_impl));
+ }
+ next_d = &next_impl->next;
+ next_impl = next_d->_impl;
+ }
+ next_d->_impl = d._impl;
+ d._impl = nullptr;
+}
+
+/// Makes a deleter that calls \c std::free() when it is destroyed.
+///
+/// \param obj object to free.
+/// \related deleter
+inline deleter make_free_deleter(void* obj) {
+ if (!obj) {
+ return deleter();
+ }
+ return deleter(deleter::raw_object_tag(), obj);
+}
+
+/// Makes a deleter that calls \c std::free() when it is destroyed, as well
+/// as invoking the encapsulated action of another deleter.
+///
+/// \param d deleter to invoke.
+/// \param obj object to free.
+/// \related deleter
+inline deleter make_free_deleter(deleter next, void* obj) {
+ return make_deleter(std::move(next), [obj] () mutable { std::free(obj); });
+}
+
+/// \see make_deleter(Object)
+/// \related deleter
+template <typename T>
+inline deleter make_object_deleter(T&& obj) {
+ return deleter{make_object_deleter_impl(deleter(), std::move(obj))};
+}
+
+/// \see make_deleter(deleter, Object)
+/// \related deleter
+template <typename T>
+inline deleter make_object_deleter(deleter d, T&& obj) {
+ return deleter{make_object_deleter_impl(std::move(d), std::move(obj))};
+}
+
+/// @}
+
+#endif /* CEPH_COMMON_DELETER_H */
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