BasicExecutionContext.hpp

//------------------------------------------------------------------------------
/*
    This file is part of clio: https://github.com/XRPLF/clio
    Copyright (c) 2024, the clio developers.
 
    Permission to use, copy, modify, and distribute this software for any
    purpose with or without fee is hereby granted, provided that the above
    copyright notice and this permission notice appear in all copies.
 
    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
//==============================================================================
 
#pragma once
 
#include "util/Assert.hpp"
#include "util/async/Concepts.hpp"
#include "util/async/Error.hpp"
#include "util/async/Operation.hpp"
#include "util/async/Outcome.hpp"
#include "util/async/context/impl/Cancellation.hpp"
#include "util/async/context/impl/Execution.hpp"
#include "util/async/context/impl/Strand.hpp"
#include "util/async/context/impl/Timer.hpp"
#include "util/async/context/impl/Utils.hpp"
#include "util/async/impl/ErrorHandling.hpp"
 
#include <boost/asio.hpp>
#include <boost/asio/error.hpp>
#include <boost/asio/strand.hpp>
#include <boost/asio/thread_pool.hpp>
 
#include <chrono>
#include <cstddef>
#include <expected>
#include <memory>
#include <optional>
#include <type_traits>
#include <utility>

namespace util::async {
namespace impl {
 
struct AsioPoolStrandContext {
    using Executor = boost::asio::strand<boost::asio::thread_pool::executor_type>;
    using Timer = SteadyTimer<Executor>;
 
    Executor&
    getExecutor()
    {
        return executor;
    }
 
    Executor executor;
};
 
struct AsioPoolContext {
    using Executor = boost::asio::thread_pool;
    using Timer = SteadyTimer<Executor>;
    using Strand = AsioPoolStrandContext;
 
    AsioPoolContext(std::size_t numThreads) : executor(std::make_unique<Executor>(numThreads))
    {
    }
 
    AsioPoolContext(AsioPoolContext const&) = delete;
    AsioPoolContext(AsioPoolContext&&) = default;
 
    Strand
    makeStrand() const
    {
        ASSERT(executor, "Called after executor was moved from.");
        return {boost::asio::make_strand(*executor)};
    }
 
    void
    stop() const
    {
        if (executor)  // don't call if executor was moved from
            executor->stop();
    }
 
    void
    join() const
    {
        if (executor)  // don't call if executor was moved from
            executor->join();
    }
 
    Executor&
    getExecutor() const
    {
        ASSERT(executor, "Called after executor was moved from.");
        return *executor;
    }
 
    std::unique_ptr<Executor> executor;
};
 
}  // namespace impl

template <
    typename ContextType,
    typename StopSourceType,
    typename DispatcherType,
    typename TimerContextProvider = impl::SelfContextProvider,
    typename ErrorHandlerType = impl::DefaultErrorHandler>
class BasicExecutionContext {
    ContextType context_;

    friend impl::AssociatedExecutorExtractor;
 
public:
    static constexpr bool kIS_NOEXCEPT = noexcept(ErrorHandlerType::wrap([](auto&) { throw 0; }));
 
    using ContextHolderType = ContextType;
 
    using ExecutorType = typename ContextHolderType::Executor;
 
    template <typename T>
    using ValueType = std::expected<T, ExecutionError>;
 
    using StopSource = StopSourceType;
 
    using StopToken = typename StopSourceType::Token;
 
    template <typename T>
    using StoppableOperation = StoppableOperation<ValueType<T>, StopSourceType>;
 
    template <typename T>
    using Operation = Operation<ValueType<T>>;
 
    using Strand = impl::
        BasicStrand<BasicExecutionContext, StopSourceType, DispatcherType, TimerContextProvider, ErrorHandlerType>;
 
    using Timer = typename ContextHolderType::Timer;
 
    // note: scheduled operations are always stoppable
    template <typename T>
    using ScheduledOperation = ScheduledOperation<BasicExecutionContext, StoppableOperation<T>>;
 
    // note: repeating operations are always stoppable and must return void
    using RepeatedOperation = RepeatingOperation<BasicExecutionContext>;

    explicit BasicExecutionContext(std::size_t numThreads = 1) noexcept : context_{numThreads}
    {
    }

    ~BasicExecutionContext()
    {
        stop();
    }
 
    BasicExecutionContext(BasicExecutionContext&&) = default;
    BasicExecutionContext(BasicExecutionContext const&) = delete;

    [[nodiscard]] auto
    scheduleAfter(
        SomeStdDuration auto delay,
        SomeHandlerWith<StopToken> auto&& fn,
        std::optional<std::chrono::milliseconds> timeout = std::nullopt
    ) noexcept(kIS_NOEXCEPT)
    {
        if constexpr (not std::is_same_v<decltype(TimerContextProvider::getContext(*this)), decltype(*this)>) {
            return TimerContextProvider::getContext(*this).scheduleAfter(
                delay, std::forward<decltype(fn)>(fn), timeout
            );
        } else {
            using FnRetType = std::decay_t<decltype(fn(std::declval<StopToken>()))>;
            return ScheduledOperation<FnRetType>(
                impl::extractAssociatedExecutor(*this),
                delay,
                [this, timeout, fn = std::forward<decltype(fn)>(fn)](auto) mutable {
                    return this->execute(
                        [fn = std::forward<decltype(fn)>(fn)](auto stopToken) {
                            if constexpr (std::is_void_v<FnRetType>) {
                                fn(std::move(stopToken));
                            } else {
                                return fn(std::move(stopToken));
                            }
                        },
                        timeout
                    );
                }
            );
        }
    }

    [[nodiscard]] auto
    scheduleAfter(
        SomeStdDuration auto delay,
        SomeHandlerWith<StopToken, bool> auto&& fn,
        std::optional<std::chrono::milliseconds> timeout = std::nullopt
    ) noexcept(kIS_NOEXCEPT)
    {
        if constexpr (not std::is_same_v<decltype(TimerContextProvider::getContext(*this)), decltype(*this)>) {
            return TimerContextProvider::getContext(*this).scheduleAfter(
                delay, std::forward<decltype(fn)>(fn), timeout
            );
        } else {
            using FnRetType = std::decay_t<decltype(fn(std::declval<StopToken>(), true))>;
            return ScheduledOperation<FnRetType>(
                impl::extractAssociatedExecutor(*this),
                delay,
                [this, timeout, fn = std::forward<decltype(fn)>(fn)](auto ec) mutable {
                    return this->execute(
                        [fn = std::forward<decltype(fn)>(fn),
                         isAborted = (ec == boost::asio::error::operation_aborted)](auto stopToken) {
                            if constexpr (std::is_void_v<FnRetType>) {
                                fn(std::move(stopToken), isAborted);
                            } else {
                                return fn(std::move(stopToken), isAborted);
                            }
                        },
                        timeout
                    );
                }
            );
        }
    }

    [[nodiscard]] auto
    executeRepeatedly(SomeStdDuration auto interval, SomeHandlerWithoutStopToken auto&& fn) noexcept(kIS_NOEXCEPT)
    {
        if constexpr (not std::is_same_v<decltype(TimerContextProvider::getContext(*this)), decltype(*this)>) {
            return TimerContextProvider::getContext(*this).executeRepeatedly(interval, std::forward<decltype(fn)>(fn));
        } else {
            return RepeatedOperation(impl::extractAssociatedExecutor(*this), interval, std::forward<decltype(fn)>(fn));
        }
    }

    [[nodiscard]] auto
    execute(
        SomeHandlerWith<StopToken> auto&& fn,
        std::optional<std::chrono::milliseconds> timeout = std::nullopt
    ) noexcept(kIS_NOEXCEPT)
    {
        return DispatcherType::dispatch(
            context_,
            impl::outcomeForHandler<StopSourceType>(fn),
            ErrorHandlerType::wrap([this, timeout, fn = std::forward<decltype(fn)>(fn)](
                                       auto& outcome, auto& stopSource, auto stopToken
                                   ) mutable {
                [[maybe_unused]] auto timeoutHandler =
                    impl::getTimeoutHandleIfNeeded(TimerContextProvider::getContext(*this), timeout, stopSource);
 
                using FnRetType = std::decay_t<decltype(fn(std::declval<StopToken>()))>;
                if constexpr (std::is_void_v<FnRetType>) {
                    fn(std::move(stopToken));
                    outcome.setValue();
                } else {
                    outcome.setValue(fn(std::move(stopToken)));
                }
            })
        );
    }

    [[nodiscard]] auto
    execute(SomeHandlerWith<StopToken> auto&& fn, SomeStdDuration auto timeout) noexcept(kIS_NOEXCEPT)
    {
        return execute(
            std::forward<decltype(fn)>(fn),
            std::make_optional(std::chrono::duration_cast<std::chrono::milliseconds>(timeout))
        );
    }

    [[nodiscard]] auto
    execute(SomeHandlerWithoutStopToken auto&& fn) noexcept(kIS_NOEXCEPT)
    {
        return DispatcherType::dispatch(
            context_,
            impl::outcomeForHandler<StopSourceType>(fn),
            ErrorHandlerType::wrap([fn = std::forward<decltype(fn)>(fn)](auto& outcome) mutable {
                using FnRetType = std::decay_t<decltype(fn())>;
                if constexpr (std::is_void_v<FnRetType>) {
                    fn();
                    outcome.setValue();
                } else {
                    outcome.setValue(fn());
                }
            })
        );
    }

    [[nodiscard]] Strand
    makeStrand()
    {
        return Strand(*this, context_.makeStrand());
    }

    void
    stop() const noexcept
    {
        context_.stop();
    }

    void
    join() const noexcept
    {
        context_.join();
    }
};

using CoroExecutionContext =
    BasicExecutionContext<impl::AsioPoolContext, impl::YieldContextStopSource, impl::SpawnDispatchStrategy>;

using PoolExecutionContext =
    BasicExecutionContext<impl::AsioPoolContext, impl::BasicStopSource, impl::PostDispatchStrategy>;
 
}  // namespace util::async