rocm-systems/source/lib/common/synchronized.hpp

// MIT License
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// Copyright (c) 2023 ROCm Developer Tools
//
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// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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#pragma once

#include <cstddef>
#include <functional>
#include <mutex>
#include <shared_mutex>
#include <type_traits>

namespace rocprofiler
{
namespace common
{
/**
 * Sychronized is a wrapper that adds lock based write/read
 * protection around a datatype. The protected data is accessed
 * only by rlock/wlock. rlock(lambda) gets a reader lock of the
 * protected value, passing the protected value to the lambda as a
 * const. wlock(lambda) gets a writer lock on the protective value
 * and does the same. The reason for this class is to make it less
 * error prone to access shared data and more obvious when a lock
 * is being held.
 *
 * Example usage:
 *
 * Synchronized<int> x(9);
 * x.rlock([](const auto& data){
 *  // data = 9
 * });
 *
 * x.wlock([](auto& data){
 *  // set data to new value
 * });
 */
template <typename LockedType, bool IsMappedTypeV = false>
class Synchronized
{
public:
    using value_type = LockedType;
    using this_type  = Synchronized<value_type, IsMappedTypeV>;

    Synchronized()  = default;
    ~Synchronized() = default;

    explicit Synchronized(value_type&& data)
    : m_data{std::move(data)}
    {}

    Synchronized(Synchronized&& data) noexcept = default;
    Synchronized& operator=(Synchronized&& data) noexcept = default;

    // Do not allow this data structure to be copied, std::move only.
    Synchronized(const Synchronized&) = delete;
    Synchronized& operator=(const Synchronized&) = delete;

    template <typename FuncT, typename... Args>
    auto rlock(FuncT&& lambda, Args&&... args) const
    {
        static_assert(std::is_invocable<FuncT, const value_type&, Args...>::value,
                      "function must accept const reference to locked type");

        auto lock = std::shared_lock{m_mutex};
        return std::forward<FuncT>(lambda)(m_data, std::forward<Args>(args)...);
    }

    template <typename FuncT, typename... Args>
    auto wlock(FuncT&& lambda, Args&&... args)
    {
        static_assert(std::is_invocable<FuncT, value_type&, Args...>::value,
                      "function must accept reference to locked type");

        auto lock = std::unique_lock{m_mutex};
        return std::forward<FuncT>(lambda)(m_data, std::forward<Args>(args)...);
    }

    // This overload to wlock allows a synchronized map whose keys map to synchronized data to
    // use a read lock on the key data and then a write lock on the mapped data.
    template <typename FuncT,
              typename... Args,
              bool EnableForMappedType                   = IsMappedTypeV,
              std::enable_if_t<EnableForMappedType, int> = 0>
    auto wlock(FuncT&& lambda, Args&&... args) const
    {
        return const_cast<this_type*>(this)->wlock(std::forward<FuncT>(lambda),
                                                   std::forward<Args>(args)...);
    }

    // Upgradable lock. If read returns false, write will be called with a unique_lock.
    // Essentially a helper function that does .rlock() followed by .wlock().
    template <typename ReadFuncT, typename WriteFuncT, typename... Args>
    bool ulock(ReadFuncT&& read, WriteFuncT&& write, Args&&... args)
    {
        static_assert(std::is_invocable<ReadFuncT, const value_type&, Args...>::value,
                      "read function must accept const reference to locked type");
        static_assert(std::is_invocable<WriteFuncT, value_type&, Args...>::value,
                      "write function must accept reference to locked type");

        using read_return_type  = std::invoke_result_t<ReadFuncT, const value_type&, Args...>;
        using write_return_type = std::invoke_result_t<WriteFuncT, value_type&, Args...>;

        static_assert(std::is_same<read_return_type, write_return_type>::value,
                      "read and write functions must return same type");
        static_assert(std::is_same<read_return_type, bool>::value,
                      "read/write functions must return bool");

        {
            auto lock = std::shared_lock{m_mutex};
            if(read(m_data, std::forward<Args>(args)...)) return true;
        }

        auto lock = std::unique_lock{m_mutex};
        return write(m_data, std::forward<Args>(args)...);
    }

private:
    mutable std::shared_mutex m_mutex = {};
    value_type                m_data  = {};
};
}  // namespace common
}  // namespace rocprofiler