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Merge pull request #1209 from yjrobin/atomic_persistent_aware_ptr
Atomic persistent-aware pointer
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‎include/libpmemobj++/experimental/atomic_persistent_aware_ptr.hpp‎

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// SPDX-License-Identifier: BSD-3-Clause
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/* Copyright 2021, Intel Corporation */
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/**
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* @file
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* Atomic specialization for persistent-aware self_relative_ptr.
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*/
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#ifndef LIBPMEMOBJ_CPP_ATOMIC_PERSISTENT_AWARE_PTR_HPP
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#define LIBPMEMOBJ_CPP_ATOMIC_PERSISTENT_AWARE_PTR_HPP
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#include <libpmemobj++/detail/atomic_backoff.hpp>
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#include <libpmemobj++/detail/common.hpp>
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#include <libpmemobj++/detail/self_relative_ptr_base_impl.hpp>
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#include <libpmemobj++/experimental/atomic_self_relative_ptr.hpp>
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#include <libpmemobj++/experimental/self_relative_ptr.hpp>
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#include <libpmemobj++/transaction.hpp>
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#include <libpmemobj++/utils.hpp>
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#include <atomic>
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namespace pmem
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{
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namespace obj
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{
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namespace experimental
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{
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/**
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* Atomic specialization of a persistent ptr (self_relative_ptr) that manages
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* its persistence by itself.
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*
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* In a multi-threaded scenario, the persistence of this ptr is guaranteed when
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* it is visible to (or read by) other threads. Performance-wise, two different
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* options are provided: Read-optimized and Write-optimized. See corresponding
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* store/load functions for details.
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*/
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template <typename T, typename ReadOptimized>
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struct atomic_persistent_aware_ptr {
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private:
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using ptr_type = pmem::detail::self_relative_ptr_base_impl<
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std::atomic<std::ptrdiff_t>>;
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using accessor = pmem::detail::self_relative_accessor<
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std::atomic<std::ptrdiff_t>>;
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static constexpr uintptr_t IS_DIRTY = 1;
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public:
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using this_type = atomic_persistent_aware_ptr;
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using value_type = pmem::obj::experimental::self_relative_ptr<T>;
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using difference_type = typename value_type::difference_type;
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constexpr atomic_persistent_aware_ptr() noexcept = default;
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/**
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* Constructors
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*/
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atomic_persistent_aware_ptr(value_type value) : ptr()
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{
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store(value);
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}
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atomic_persistent_aware_ptr(const atomic_persistent_aware_ptr &) =
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delete;
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/**
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* Read-optimized store does the flush in store function, and clear the
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* dirty marker after flush.
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*
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* @param[in] desired the self_relative_ptr (no dirty flag) to be stored
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*
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*/
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template <typename OPT = ReadOptimized>
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typename std::enable_if<std::is_same<OPT, std::true_type>::value>::type
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store(value_type desired,
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std::memory_order order = std::memory_order_seq_cst) noexcept
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{
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auto dirty_desired = mark_dirty(desired);
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ptr.store(dirty_desired, order);
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pool_by_vptr(this).persist(&ptr, sizeof(ptr));
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ptr.compare_exchange_strong(dirty_desired, clear_dirty(desired),
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order);
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/* Flushing is not necessary for correctness, it's enough that
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* dirty_desired is persistent */
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#if LIBPMEMOBJ_CPP_VG_PMEMCHECK_ENABLED
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VALGRIND_PMC_DO_FLUSH(&ptr, sizeof(ptr));
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#endif
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}
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/**
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* Write-optimized store updates the ptr with the dirty flag, relies on
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* consequent load to do the flush.
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*
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* @param[in] desired the self_relative_ptr (no dirty flag) to be stored
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*
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*/
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template <typename OPT = ReadOptimized>
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typename std::enable_if<!std::is_same<OPT, std::true_type>::value>::type
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store(value_type desired,
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std::memory_order order = std::memory_order_seq_cst) noexcept
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{
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ptr.store(mark_dirty(desired), order);
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}
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/**
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* Read-optimized load retries upon dirty ptr, relies on the store
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* function to clear the dirty before continue.
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* But for correctness, just flush the dirty ptr and return the clear
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* ptr for now.
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*
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* @return the self_relative_ptr (no dirty flag)
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*/
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template <typename OPT = ReadOptimized>
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typename std::enable_if<std::is_same<OPT, std::true_type>::value,
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value_type>::type
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load(std::memory_order order = std::memory_order_seq_cst) noexcept
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{
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auto val = ptr.load(order);
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if (is_dirty(val)) {
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pool_by_vptr(this).persist(&ptr, sizeof(ptr));
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}
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return clear_dirty(val);
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}
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/**
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* Write-optimized load flushes the ptr with the dirty flag, clears the
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* flag using CAS after flush.
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* If CAS failed, simply return the old clear ptr, rely on later load to
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* clear the dirty flag.
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*
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* @return the self_relative_ptr (no dirty flag)
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*/
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template <typename OPT = ReadOptimized>
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typename std::enable_if<!std::is_same<OPT, std::true_type>::value,
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value_type>::type
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load(std::memory_order order = std::memory_order_seq_cst) noexcept
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{
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auto val = ptr.load(order);
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if (is_dirty(val)) {
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pool_by_vptr(this).persist(&ptr, sizeof(ptr));
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auto clear_val = clear_dirty(val);
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ptr.compare_exchange_strong(val, clear_val, order);
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#if LIBPMEMOBJ_CPP_VG_PMEMCHECK_ENABLED
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VALGRIND_PMC_DO_FLUSH(&ptr, sizeof(ptr));
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#endif
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return clear_val;
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}
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return clear_dirty(val);
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}
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bool
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is_lock_free() const noexcept
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{
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return ptr.is_lock_free();
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}
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/*
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* Operators
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*/
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operator value_type() const noexcept
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{
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return load();
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}
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value_type
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operator=(value_type desired) noexcept
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{
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store(desired);
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return desired;
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}
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private:
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value_type
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mark_dirty(value_type ptr) const
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{
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auto dirty_ptr =
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reinterpret_cast<uintptr_t>(ptr.get()) | IS_DIRTY;
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return value_type{reinterpret_cast<T *>(dirty_ptr)};
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}
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value_type
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clear_dirty(value_type ptr) const
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{
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auto clear_ptr =
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reinterpret_cast<uintptr_t>(ptr.get()) & ~IS_DIRTY;
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return value_type{reinterpret_cast<T *>(clear_ptr)};
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}
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bool
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is_dirty(value_type ptr) const
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{
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return reinterpret_cast<uintptr_t>(ptr.get()) & IS_DIRTY;
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}
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std::atomic<self_relative_ptr<T>> ptr;
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};
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} // namespace experimental
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} // namespace obj
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} // namespace pmem
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#endif // LIBPMEMOBJ_CPP_ATOMIC_PERSISTENT_AWARE_PTR_HPP

‎tests/CMakeLists.txt‎

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build_test(self_relative_ptr_atomic_pmem ptr/self_relative_ptr_atomic_pmem.cpp)
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add_test_generic(NAME self_relative_ptr_atomic_pmem TRACERS none memcheck pmemcheck drd helgrind)
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build_test(atomic_persistent_aware_ptr_pmem ptr/atomic_persistent_aware_ptr_pmem.cpp)
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add_test_generic(NAME atomic_persistent_aware_ptr_pmem TRACERS none memcheck pmemcheck drd helgrind)
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endif()
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add_subdirectory(external)

‎tests/ptr/atomic_persistent_aware_ptr_pmem.cpp‎

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// SPDX-License-Identifier: BSD-3-Clause
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/* Copyright 2021, Intel Corporation */
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#include "thread_helpers.hpp"
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#include "unittest.hpp"
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#include <libpmemobj++/experimental/atomic_persistent_aware_ptr.hpp>
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#include <libpmemobj++/experimental/self_relative_ptr.hpp>
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#include <libpmemobj++/make_persistent.hpp>
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#include <libpmemobj++/make_persistent_array_atomic.hpp>
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#include <libpmemobj++/make_persistent_atomic.hpp>
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#include <libpmemobj++/p.hpp>
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#include <libpmemobj++/persistent_ptr.hpp>
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#include <libpmemobj++/persistent_ptr_base.hpp>
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#include <libpmemobj++/pool.hpp>
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#include <libpmemobj++/transaction.hpp>
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#define LAYOUT "cpp"
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namespace nvobj = pmem::obj;
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template <typename T>
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using self_relative_ptr = pmem::obj::experimental::self_relative_ptr<T>;
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template <typename T, typename ReadOptimized>
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using atomic_ptr =
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pmem::obj::experimental::atomic_persistent_aware_ptr<T, ReadOptimized>;
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template <typename ReadOptimized>
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struct root {
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atomic_ptr<int, ReadOptimized> ptr;
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self_relative_ptr<int> non_atomic_ptr;
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};
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namespace
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{
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template <typename ReadOptimized>
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void
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test_ptr_allocation(nvobj::pool<root<ReadOptimized>> &pop)
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{
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auto r = pop.root();
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try {
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nvobj::transaction::run(pop, [&] {
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UT_ASSERT(r->ptr.load() == nullptr);
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r->non_atomic_ptr = nvobj::make_persistent<int>();
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});
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r->ptr.store(r->non_atomic_ptr);
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} catch (...) {
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ASSERT_UNREACHABLE;
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}
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UT_ASSERT(r->ptr.load() != nullptr);
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try {
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auto non_atomic_ptr = r->ptr.load();
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nvobj::transaction::run(pop, [&] {
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nvobj::delete_persistent<int>(non_atomic_ptr);
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});
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r->ptr.store(nullptr);
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} catch (...) {
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ASSERT_UNREACHABLE;
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}
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UT_ASSERT(r->ptr.load() == nullptr);
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}
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} /* namespace */
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inline const char *const
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BoolToString(bool b)
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{
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return b ? "_ropt" : "_wopt";
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}
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template <typename ReadOptimized>
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static void
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test(char *path)
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{
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std::string path_str(path);
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path_str += BoolToString(ReadOptimized::value);
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nvobj::pool<root<ReadOptimized>> pop;
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try {
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pop = nvobj::pool<root<ReadOptimized>>::create(
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path_str, LAYOUT, PMEMOBJ_MIN_POOL, S_IWUSR | S_IRUSR);
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} catch (pmem::pool_error &pe) {
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UT_FATAL("!pool::create: %s %s", pe.what(), path_str.c_str());
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}
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test_ptr_allocation(pop);
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pop.close();
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}
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int
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main(int argc, char *argv[])
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{
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if (argc != 2)
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UT_FATAL("usage: %s file-name", argv[0]);
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auto ret_writeopt = run_test([&] { test<std::false_type>(argv[1]); });
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auto ret_readopt = run_test([&] { test<std::true_type>(argv[1]); });
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return (ret_writeopt && ret_readopt);
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}

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