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ChancellorIkseew
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#ifndef ENTT_PROCESS_PROCESS_HPP
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#define ENTT_PROCESS_PROCESS_HPP
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#include <cstdint>
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#include <type_traits>
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#include <utility>
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#include "fwd.hpp"
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namespace entt {
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/**
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* @brief Base class for processes.
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*
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* This class stays true to the CRTP idiom. Derived classes must specify what's
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* the intended type for elapsed times.<br/>
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* A process should expose publicly the following member functions whether
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* required:
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*
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* * @code{.cpp}
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* void update(Delta, void *);
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* @endcode
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*
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* It's invoked once per tick until a process is explicitly aborted or it
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* terminates either with or without errors. Even though it's not mandatory to
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* declare this member function, as a rule of thumb each process should at
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* least define it to work properly. The `void *` parameter is an opaque
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* pointer to user data (if any) forwarded directly to the process during an
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* update.
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*
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* * @code{.cpp}
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* void init();
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* @endcode
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*
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* It's invoked when the process joins the running queue of a scheduler. This
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* happens as soon as it's attached to the scheduler if the process is a top
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* level one, otherwise when it replaces its parent if the process is a
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* continuation.
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*
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* * @code{.cpp}
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* void succeeded();
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* @endcode
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*
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* It's invoked in case of success, immediately after an update and during the
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* same tick.
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*
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* * @code{.cpp}
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* void failed();
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* @endcode
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*
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* It's invoked in case of errors, immediately after an update and during the
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* same tick.
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*
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* * @code{.cpp}
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* void aborted();
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* @endcode
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*
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* It's invoked only if a process is explicitly aborted. There is no guarantee
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* that it executes in the same tick, this depends solely on whether the
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* process is aborted immediately or not.
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*
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* Derived classes can change the internal state of a process by invoking the
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* `succeed` and `fail` protected member functions and even pause or unpause the
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* process itself.
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*
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* @sa scheduler
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*
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* @tparam Derived Actual type of process that extends the class template.
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* @tparam Delta Type to use to provide elapsed time.
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*/
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template<typename Derived, typename Delta>
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class process {
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enum class state : std::uint8_t {
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uninitialized = 0,
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running,
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paused,
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succeeded,
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failed,
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aborted,
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finished,
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rejected
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};
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template<typename Target = Derived>
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auto next(std::integral_constant<state, state::uninitialized>)
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-> decltype(std::declval<Target>().init(), void()) {
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static_cast<Target *>(this)->init();
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}
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template<typename Target = Derived>
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auto next(std::integral_constant<state, state::running>, Delta delta, void *data)
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-> decltype(std::declval<Target>().update(delta, data), void()) {
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static_cast<Target *>(this)->update(delta, data);
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}
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template<typename Target = Derived>
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auto next(std::integral_constant<state, state::succeeded>)
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-> decltype(std::declval<Target>().succeeded(), void()) {
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static_cast<Target *>(this)->succeeded();
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}
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template<typename Target = Derived>
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auto next(std::integral_constant<state, state::failed>)
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-> decltype(std::declval<Target>().failed(), void()) {
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static_cast<Target *>(this)->failed();
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}
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template<typename Target = Derived>
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auto next(std::integral_constant<state, state::aborted>)
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-> decltype(std::declval<Target>().aborted(), void()) {
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static_cast<Target *>(this)->aborted();
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}
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void next(...) const noexcept {}
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protected:
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/**
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* @brief Terminates a process with success if it's still alive.
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*
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* The function is idempotent and it does nothing if the process isn't
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* alive.
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*/
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void succeed() noexcept {
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if(alive()) {
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current = state::succeeded;
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}
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}
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/**
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* @brief Terminates a process with errors if it's still alive.
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*
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* The function is idempotent and it does nothing if the process isn't
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* alive.
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*/
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void fail() noexcept {
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if(alive()) {
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current = state::failed;
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}
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}
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/**
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* @brief Stops a process if it's in a running state.
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*
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* The function is idempotent and it does nothing if the process isn't
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* running.
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*/
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void pause() noexcept {
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if(current == state::running) {
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current = state::paused;
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}
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}
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/**
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* @brief Restarts a process if it's paused.
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*
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* The function is idempotent and it does nothing if the process isn't
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* paused.
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*/
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void unpause() noexcept {
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if(current == state::paused) {
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current = state::running;
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}
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}
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public:
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/*! @brief Type used to provide elapsed time. */
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using delta_type = Delta;
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/*! @brief Default destructor. */
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virtual ~process() noexcept {
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static_assert(std::is_base_of_v<process, Derived>, "Incorrect use of the class template");
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}
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/**
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* @brief Aborts a process if it's still alive.
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*
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* The function is idempotent and it does nothing if the process isn't
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* alive.
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*
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* @param immediate Requests an immediate operation.
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*/
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void abort(const bool immediate = false) {
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if(alive()) {
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current = state::aborted;
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if(immediate) {
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tick({});
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}
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}
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}
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/**
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* @brief Returns true if a process is either running or paused.
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* @return True if the process is still alive, false otherwise.
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*/
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[[nodiscard]] bool alive() const noexcept {
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return current == state::running || current == state::paused;
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}
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/**
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* @brief Returns true if a process is already terminated.
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* @return True if the process is terminated, false otherwise.
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*/
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[[nodiscard]] bool finished() const noexcept {
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return current == state::finished;
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}
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/**
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* @brief Returns true if a process is currently paused.
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* @return True if the process is paused, false otherwise.
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*/
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[[nodiscard]] bool paused() const noexcept {
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return current == state::paused;
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}
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/**
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* @brief Returns true if a process terminated with errors.
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* @return True if the process terminated with errors, false otherwise.
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*/
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[[nodiscard]] bool rejected() const noexcept {
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return current == state::rejected;
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}
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/**
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* @brief Updates a process and its internal state if required.
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* @param delta Elapsed time.
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* @param data Optional data.
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*/
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void tick(const Delta delta, void *data = nullptr) {
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switch(current) {
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case state::uninitialized:
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next(std::integral_constant<state, state::uninitialized>{});
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current = state::running;
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break;
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case state::running:
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next(std::integral_constant<state, state::running>{}, delta, data);
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break;
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default:
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// suppress warnings
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break;
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}
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// if it's dead, it must be notified and removed immediately
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switch(current) {
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case state::succeeded:
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next(std::integral_constant<state, state::succeeded>{});
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current = state::finished;
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break;
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case state::failed:
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next(std::integral_constant<state, state::failed>{});
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current = state::rejected;
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break;
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case state::aborted:
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next(std::integral_constant<state, state::aborted>{});
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current = state::rejected;
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break;
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default:
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// suppress warnings
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break;
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}
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}
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private:
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state current{state::uninitialized};
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};
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/**
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* @brief Adaptor for lambdas and functors to turn them into processes.
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*
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* Lambdas and functors can't be used directly with a scheduler for they are not
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* properly defined processes with managed life cycles.<br/>
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* This class helps in filling the gap and turning lambdas and functors into
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* full featured processes usable by a scheduler.
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*
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* The signature of the function call operator should be equivalent to the
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* following:
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*
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* @code{.cpp}
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* void(Delta delta, void *data, auto succeed, auto fail);
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* @endcode
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*
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* Where:
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*
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* * `delta` is the elapsed time.
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* * `data` is an opaque pointer to user data if any, `nullptr` otherwise.
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* * `succeed` is a function to call when a process terminates with success.
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* * `fail` is a function to call when a process terminates with errors.
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*
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* The signature of the function call operator of both `succeed` and `fail`
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* is equivalent to the following:
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*
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* @code{.cpp}
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* void();
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* @endcode
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*
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* Usually users shouldn't worry about creating adaptors. A scheduler will
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* create them internally each and avery time a lambda or a functor is used as
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* a process.
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*
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* @sa process
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* @sa scheduler
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*
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* @tparam Func Actual type of process.
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* @tparam Delta Type to use to provide elapsed time.
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*/
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template<typename Func, typename Delta>
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struct process_adaptor: process<process_adaptor<Func, Delta>, Delta>, private Func {
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/**
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* @brief Constructs a process adaptor from a lambda or a functor.
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* @tparam Args Types of arguments to use to initialize the actual process.
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* @param args Parameters to use to initialize the actual process.
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*/
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template<typename... Args>
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process_adaptor(Args &&...args)
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: Func{std::forward<Args>(args)...} {}
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/**
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* @brief Updates a process and its internal state if required.
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* @param delta Elapsed time.
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* @param data Optional data.
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*/
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void update(const Delta delta, void *data) {
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Func::operator()(
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delta,
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data,
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[this]() { this->succeed(); },
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[this]() { this->fail(); });
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}
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};
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} // namespace entt
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#endif
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