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+/*
+ This file is part of Raul.
+ Copyright 2007-2017 David Robillard <http://drobilla.net>
+
+ Raul is free software: you can redistribute it and/or modify it under the
+ terms of the GNU General Public License as published by the Free Software
+ Foundation, either version 3 of the License, or any later version.
+
+ Raul is distributed in the hope that it will be useful, but WITHOUT ANY
+ WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+ A PARTICULAR PURPOSE. See the GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with Raul. If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#ifndef RAUL_MAID_HPP
+#define RAUL_MAID_HPP
+
+#include <atomic>
+#include <memory>
+
+#include "raul/Deletable.hpp"
+#include "raul/Noncopyable.hpp"
+
+namespace Raul {
+
+/** Explicit garbage-collector.
+ *
+ * This allows objects to be disposed of in a real-time thread, but actually
+ * deleted later by another thread which calls cleanup(). Disposable objects
+ * may be explicitly disposed by calling dispose(), or automatically managed
+ * with a managed_ptr which can safely be dropped in any thread, including
+ * real-time threads.
+ *
+ * \ingroup raul
+ */
+class Maid : public Noncopyable
+{
+public:
+ /** An object that can be disposed via Maid::dispose(). */
+ class Disposable : public Deletable {
+ public:
+ Disposable() : _maid_next(nullptr) {}
+
+ private:
+ friend class Maid;
+ Disposable* _maid_next;
+ };
+
+ /** Disposable wrapper for any type. */
+ template<typename T>
+ class Managed : public Raul::Maid::Disposable, public T
+ {
+ public:
+ template<typename... Args>
+ Managed(Args&&... args)
+ : T(std::forward<Args>(args)...)
+ {}
+ };
+
+ /** Deleter for Disposable objects. */
+ template<typename T>
+ class Disposer {
+ public:
+ Disposer(Maid& maid) : _maid(&maid) {}
+ Disposer() : _maid(nullptr) {}
+
+ void operator()(T* obj) {
+ if (_maid) { _maid->dispose(obj); }
+ }
+
+ Maid* _maid;
+ };
+
+ /** A managed pointer that automatically disposes of its contents.
+ *
+ * This is a unique_ptr so that it is possible to statically verify that
+ * code is real-time safe.
+ */
+ template<typename T> using managed_ptr = std::unique_ptr<T, Disposer<T>>;
+
+ Maid() : _disposed(nullptr) {}
+
+ inline ~Maid() { cleanup(); }
+
+ /** Return false iff there is currently no garbage. */
+ inline bool empty() const {
+ return !(bool)_disposed.load(std::memory_order_relaxed);
+ }
+
+ /** Enqueue an object for deletion when cleanup() is called next.
+ *
+ * This is thread-safe, and real-time safe assuming reasonably low
+ * contention.
+ */
+ inline void dispose(Disposable* obj) {
+ if (obj) {
+ // Atomically add obj to the head of the disposed list
+ do {
+ obj->_maid_next = _disposed.load(std::memory_order_relaxed);
+ } while (!_disposed.compare_exchange_weak(
+ obj->_maid_next, obj,
+ std::memory_order_release,
+ std::memory_order_relaxed));
+ }
+ }
+
+ /** Delete all disposed objects immediately.
+ *
+ * Obviously not real-time safe, but may be called while other threads are
+ * calling dispose().
+ */
+ inline void cleanup() {
+ // Atomically get the head of the disposed list
+ Disposable* const disposed = _disposed.exchange(
+ nullptr, std::memory_order_acquire);
+
+ // Free the disposed list
+ for (Disposable* obj = disposed; obj;) {
+ Disposable* const next = obj->_maid_next;
+ delete obj;
+ obj = next;
+ }
+ }
+
+ /** Make a unique_ptr that will dispose its object when dropped. */
+ template<class T, class... Args>
+ managed_ptr<T> make_managed(Args&&... args) {
+ T* obj = new T(std::forward<Args>(args)...);
+ return std::unique_ptr<T, Disposer<T> >(obj, Disposer<T>(*this));
+ }
+
+private:
+ std::atomic<Disposable*> _disposed;
+};
+
+template<typename T>
+using managed_ptr = Maid::managed_ptr<T>;
+
+} // namespace Raul
+
+#endif // RAUL_MAID_HPP