FastRef.h

/*
 * FastRef.h
 *
 * This source file is part of the FoundationDB open source project
 *
 * Copyright 2013-2018 Apple Inc. and the FoundationDB project authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * 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.
 */

#ifndef FLOW_FASTREF_H
#define FLOW_FASTREF_H
#pragma once

#include <cstdint>

#include "flow/Platform.h"

#if VALGRIND
#include <drd.h>
#endif

template <class Subclass>
class ThreadSafeReferenceCounted {
public:
	ThreadSafeReferenceCounted() : referenceCount(1) {}
	// NO virtual destructor!  Subclass should have a virtual destructor if it is not sealed.
	void addref() const {
		interlockedIncrement(&referenceCount);
	}
	// If return value is true, caller is responsible for destruction of object
	bool delref_no_destroy() const {
		if (interlockedDecrement(&referenceCount) != 0) {
#ifdef VALGRIND
			ANNOTATE_HAPPENS_BEFORE(&referenceCount);
#endif
			return false;
		}
#ifdef VALGRIND
		ANNOTATE_HAPPENS_AFTER(&referenceCount);
#endif
		return true;
	}
	void delref() const {
		if (delref_no_destroy())
			delete (Subclass*)this;
	}
	void setrefCountUnsafe(int32_t count) const { referenceCount = count; }
	int32_t debugGetReferenceCount() const { return referenceCount; }	// Never use in production code, only for tracing
	bool isSoleOwnerUnsafe() const { return referenceCount == 1; }
private:
	ThreadSafeReferenceCounted(const ThreadSafeReferenceCounted&) /* = delete*/;
	void operator=(const ThreadSafeReferenceCounted&) /* = delete*/;
	mutable volatile int32_t referenceCount;
};

template <class Subclass>
class ThreadUnsafeReferenceCounted {
public:
	ThreadUnsafeReferenceCounted() : referenceCount(1) {}
	// NO virtual destructor!  Subclass should have a virtual destructor if it is not sealed.
	void addref() const { ++referenceCount; }
	void delref() const {
		if (delref_no_destroy())
			delete (Subclass*)this;
	}
	bool delref_no_destroy() const { return !--referenceCount; }
	int32_t debugGetReferenceCount() const { return referenceCount; }	// Never use in production code, only for tracing
	bool isSoleOwner() const { return referenceCount == 1; }
private:
	ThreadUnsafeReferenceCounted(const ThreadUnsafeReferenceCounted&) /* = delete*/;
	void operator=(const ThreadUnsafeReferenceCounted&) /* = delete*/;
	mutable int32_t referenceCount;
};

#if FLOW_THREAD_SAFE
#define ReferenceCounted ThreadSafeReferenceCounted
#else
#define ReferenceCounted ThreadUnsafeReferenceCounted
#endif

template <class P>
void addref( P* ptr ) { ptr->addref(); }

template <class P>
void delref( P* ptr ) { ptr->delref(); }

template <class P>
class Reference
{
public:
	Reference() : ptr(NULL) {}
	explicit Reference( P* ptr ) : ptr(ptr) {}
	static Reference<P> addRef( P* ptr ) { ptr->addref(); return Reference(ptr); }

	Reference(const Reference& r) : ptr(r.getPtr()) { if (ptr) addref(ptr); }
	Reference(Reference && r) BOOST_NOEXCEPT : ptr(r.getPtr()) { r.ptr = NULL; }

	template <class Q>
	Reference(const Reference<Q>& r) : ptr(r.getPtr()) { if (ptr) addref(ptr); }
	template <class Q>
	Reference(Reference<Q> && r) : ptr(r.getPtr()) { r.setPtrUnsafe(NULL); }

	~Reference() { if (ptr) delref(ptr); }
	Reference& operator=(const Reference& r) {
		P* oldPtr = ptr;
		P* newPtr = r.ptr;
		if (oldPtr != newPtr) {
			if (newPtr) addref(newPtr);
			ptr = newPtr;
			if (oldPtr) delref(oldPtr);
		}
		return *this;
	}
	Reference& operator=(Reference&& r) BOOST_NOEXCEPT {
		P* oldPtr = ptr;
		P* newPtr = r.ptr;
		if (oldPtr != newPtr) {
			r.ptr = NULL;
			ptr = newPtr;
			if (oldPtr) delref(oldPtr);
		}
		return *this;
	}

	void clear() {
		P* oldPtr = ptr;
		if (oldPtr) {
			ptr = NULL;
			delref(oldPtr);
		}
	}

	P* operator->() const { return ptr; }
	P& operator*() const { return *ptr; }
	P* getPtr() const { return ptr; }

	void setPtrUnsafe( P* p ) { ptr = p; }

	P* extractPtr() { auto *p = ptr; ptr = NULL; return p; }

	template <class T>
	Reference<T> castTo() {
		return Reference<T>::addRef((T*)ptr);
	}

	bool isValid() const { return ptr != NULL; }
	explicit operator bool() const { return ptr != NULL; }

private:
	P *ptr;
};

template <class P>
bool operator==( const Reference<P>& lhs, const Reference<P>& rhs ) {
	return lhs.getPtr() == rhs.getPtr();
}

#endif