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// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
#pragma once
#include "entryref.h"
#include <atomic>
namespace vespalib::datastore {
/**
* A wrapper for std::atomic of type EntryRef that supports copy and move constructors and assignment operator,
* and uses Release-Acquire ordering for store and load.
*
* Use this class when entry refs are stored in data stores or rcu vectors,
* where copy and move constructors and assignment operator are needed when resizing underlying buffers.
* In this case synchronization between the writer thread and reader threads
* is handled as part of the buffer switch.
*/
class AtomicEntryRef {
private:
std::atomic<uint32_t> _ref;
public:
AtomicEntryRef() noexcept : _ref() {}
explicit AtomicEntryRef(EntryRef ref) noexcept : _ref(ref.ref()) {}
AtomicEntryRef(const AtomicEntryRef& rhs) noexcept : _ref(rhs._ref.load(std::memory_order_relaxed)) {}
AtomicEntryRef(AtomicEntryRef&& rhs) noexcept : _ref(rhs._ref.load(std::memory_order_relaxed)) {}
AtomicEntryRef& operator=(const AtomicEntryRef& rhs) noexcept {
uint32_t ref = rhs._ref.load(std::memory_order_relaxed);
_ref.store(ref, std::memory_order_relaxed);
return *this;
}
void store_release(EntryRef ref) noexcept {
_ref.store(ref.ref(), std::memory_order_release);
}
void store_relaxed(EntryRef ref) noexcept {
_ref.store(ref.ref(), std::memory_order_relaxed);
}
EntryRef load_acquire() const noexcept {
return EntryRef(_ref.load(std::memory_order_acquire));
}
EntryRef load_relaxed() const noexcept {
return EntryRef(_ref.load(std::memory_order_relaxed));
}
};
vespalib::asciistream& operator<<(vespalib::asciistream& os, const AtomicEntryRef& ref);
}
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