From 7d4934534e9c58a111215859ba83c32a9bc0fa8a Mon Sep 17 00:00:00 2001
From: Mat <mail@mathias.is>
Date: Thu, 5 Mar 2020 12:52:34 +0200
Subject: Stabilise MoveToWorld (#4004)

* Stabilise MoveToWorld

* Fix comments and deprecate ScheduleMoveToWorld

* Enhanced thread safety for m_WorldChangeInfo

* Return unique_ptr from cAtomicUniquePtr::exchange

* cWorld now calls entity cEntity::OnAddToWorld and cEntity::OnRemoveFromWorld.

Allows broadcasting entities added to the world from the world's tick thread.
This also factors out some common code from cEntity::DoMoveToWorld and cEntity::Initialize.

As a consequence, cEntity::Destroy(false) (i.e. Destroying the entity without broadcasting) is impossible.
This isn't used anywhere in Cuberite so it's now deprecated.

* Update entity position after removing it from the world.
Fixes broadcasts being sent to the wrong chunk.

* Fix style

* cEntity: Update LastSentPosition when sending spawn packet

* Add Wno-deprecated-declarations to the lua bindings

* Kill uses of ScheduleMoveToWorld
---
 src/OSSupport/AtomicUniquePtr.h | 81 +++++++++++++++++++++++++++++++++++++++++
 src/OSSupport/CMakeLists.txt    |  1 +
 2 files changed, 82 insertions(+)
 create mode 100644 src/OSSupport/AtomicUniquePtr.h

(limited to 'src/OSSupport')

diff --git a/src/OSSupport/AtomicUniquePtr.h b/src/OSSupport/AtomicUniquePtr.h
new file mode 100644
index 000000000..5b18763d3
--- /dev/null
+++ b/src/OSSupport/AtomicUniquePtr.h
@@ -0,0 +1,81 @@
+
+
+#pragma once
+
+
+/** An RAII wrapper for std::atomic<T*>. */
+template <typename T>
+class cAtomicUniquePtr
+{
+public:
+	static_assert(!std::is_array<T>::value, "cAtomicUniquePtr does not support arrays");
+	DISALLOW_COPY_AND_ASSIGN(cAtomicUniquePtr);
+
+	cAtomicUniquePtr() NOEXCEPT:
+		m_Ptr(nullptr)
+	{
+	}
+
+
+	cAtomicUniquePtr(std::unique_ptr<T> a_Ptr) NOEXCEPT:
+		m_Ptr(a_Ptr.release())
+	{
+	}
+
+	cAtomicUniquePtr & operator = (std::unique_ptr<T> a_Ptr) NOEXCEPT
+	{
+		store(std::move(a_Ptr));
+		return *this;
+	}
+
+	~cAtomicUniquePtr() NOEXCEPT
+	{
+		delete load();
+	}
+
+	operator T * () const NOEXCEPT
+	{
+		return load();
+	}
+
+	bool compare_exchange_weak(T *& a_Expected, std::unique_ptr<T> && a_Desired, std::memory_order a_Order = std::memory_order_seq_cst) NOEXCEPT
+	{
+		bool DidExchange = m_Ptr.compare_exchange_weak(a_Expected, a_Desired.get(), a_Order);
+		if (DidExchange)
+		{
+			// Only release ownership from the caller if the exchange occurred
+			a_Desired.release();
+		}
+		return DidExchange;
+	}
+
+	bool compare_exchange_strong(T *& a_Expected, std::unique_ptr<T> && a_Desired, std::memory_order a_Order = std::memory_order_seq_cst) NOEXCEPT
+	{
+		bool DidExchange = m_Ptr.compare_exchange_strong(a_Expected, a_Desired.get(), a_Order);
+		if (DidExchange)
+		{
+			// Only release ownership from the caller if the exchange occurred
+			a_Desired.release();
+		}
+		return DidExchange;
+	}
+
+	std::unique_ptr<T> exchange(std::unique_ptr<T> a_Ptr, std::memory_order a_Order = std::memory_order_seq_cst) NOEXCEPT
+	{
+		return std::unique_ptr<T>{ m_Ptr.exchange(a_Ptr.release(), a_Order) };
+	}
+
+	T * load(std::memory_order a_Order = std::memory_order_seq_cst) const NOEXCEPT
+	{
+		return m_Ptr.load(a_Order);
+	}
+
+	void store(std::unique_ptr<T> a_Ptr, std::memory_order a_Order = std::memory_order_seq_cst) NOEXCEPT
+	{
+		// Store new value and delete old value
+		delete m_Ptr.exchange(a_Ptr.release(), a_Order);
+	}
+
+private:
+	std::atomic<T*> m_Ptr;
+};
diff --git a/src/OSSupport/CMakeLists.txt b/src/OSSupport/CMakeLists.txt
index 332b880ed..9f3fcb8a0 100644
--- a/src/OSSupport/CMakeLists.txt
+++ b/src/OSSupport/CMakeLists.txt
@@ -19,6 +19,7 @@ SET (SRCS
 )
 
 SET (HDRS
+	AtomicUniquePtr.h
 	CriticalSection.h
 	Errors.h
 	Event.h
-- 
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