Solver.hpp

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// -------------------------------------------------------//
//
// SHAMROCK code for hydrodynamics
// Copyright (c) 2021-2026 Timothée David--Cléris <tim.shamrock@proton.me>
// SPDX-License-Identifier: CeCILL Free Software License Agreement v2.1
// Shamrock is licensed under the CeCILL 2.1 License, see LICENSE for more information
//
// -------------------------------------------------------//
 
#pragma once

 
#include "shambase/exception.hpp"
#include "SolverConfig.hpp"
#include "shambackends/vec.hpp"
#include "shammodels/sph/BasicSPHGhosts.hpp"
#include "shammodels/sph/SPHUtilities.hpp"
#include "shammodels/sph/SolverLog.hpp"
#include "shammodels/sph/modules/SolverStorage.hpp"
#include "shamrock/patch/PatchDataLayerLayout.hpp"
#include "shamrock/scheduler/ComputeField.hpp"
#include "shamrock/scheduler/InterfacesUtility.hpp"
#include "shamrock/scheduler/SerialPatchTree.hpp"
#include "shamrock/scheduler/ShamrockCtx.hpp"
#include "shamsys/legacy/log.hpp"
#include "shamtree/TreeTraversalCache.hpp"
#include <functional>
#include <limits>
#include <memory>
#include <optional>
#include <stdexcept>
#include <variant>
#include <vector>
namespace shammodels::sph {
 
    struct TimestepLog {
        i32 rank;
        f64 rate;
        u64 npart;
        f64 tcompute;
 
        inline f64 rate_sum() { return shamalgs::collective::allreduce_sum(rate); }
 
        inline u64 npart_sum() { return shamalgs::collective::allreduce_sum(npart); }
 
        inline f64 tcompute_max() { return shamalgs::collective::allreduce_max(tcompute); }
    };
 
    struct EvolveUntilResults {
        bool reach_target_time;
        bool reach_niter_max;
        bool reach_max_walltime;
 
        i32 iter_count;
    };

    template<class Tvec, template<class> class SPHKernel>
    class Solver {
        public:
        using Tscal              = shambase::VecComponent<Tvec>;
        static constexpr u32 dim = shambase::VectorProperties<Tvec>::dimension;
        using Kernel             = SPHKernel<Tscal>;
 
        using Config = SolverConfig<Tvec, SPHKernel>;
 
        using u_morton = typename Config::u_morton;
 
        static constexpr Tscal Rkern = Kernel::Rkern;
 
        ShamrockCtx &context;
        inline PatchScheduler &scheduler() { return shambase::get_check_ref(context.sched); }
 
        SolverStorage<Tvec, u_morton> storage{};
 
        Config solver_config;
        SolverLog solve_logs;
 
        struct SolverStepCallback {
            std::optional<std::function<void(void)>> step_begin_callback;
            std::optional<std::function<void(void)>> step_end_callback;
        };
        std::vector<SolverStepCallback> timestep_callbacks{};
 
        inline void init_required_fields() { solver_config.set_layout(context.get_pdl_write()); }
 
        // serial patch tree control
        void gen_serial_patch_tree();
        inline void reset_serial_patch_tree() { storage.serial_patch_tree.reset(); }
 
        // interface_control
        using GhostHandle      = sph::BasicSPHGhostHandler<Tvec>;
        using GhostHandleCache = typename GhostHandle::CacheMap;
 
        inline void gen_ghost_handler(Tscal time_val) {
 
            using CfgClass = sph::BasicSPHGhostHandlerConfig<Tvec>;
            using BCConfig = typename CfgClass::Variant;
 
            using BCFree             = typename CfgClass::Free;
            using BCPeriodic         = typename CfgClass::Periodic;
            using BCShearingPeriodic = typename CfgClass::ShearingPeriodic;
 
            using SolverConfigBC           = typename Config::BCConfig;
            using SolverBCFree             = typename SolverConfigBC::Free;
            using SolverBCPeriodic         = typename SolverConfigBC::Periodic;
            using SolverBCShearingPeriodic = typename SolverConfigBC::ShearingPeriodic;
 
            // boundary condition selections
            if (SolverBCFree *c
                = std::get_if<SolverBCFree>(&solver_config.boundary_config.config)) {
                storage.ghost_handler.set(
                    GhostHandle{
                        scheduler(),
                        BCFree{},
                        storage.patch_rank_owner,
                        storage.xyzh_ghost_layout});
            } else if (
                SolverBCPeriodic *c
                = std::get_if<SolverBCPeriodic>(&solver_config.boundary_config.config)) {
                storage.ghost_handler.set(
                    GhostHandle{
                        scheduler(),
                        BCPeriodic{},
                        storage.patch_rank_owner,
                        storage.xyzh_ghost_layout});
            } else if (
                SolverBCShearingPeriodic *c
                = std::get_if<SolverBCShearingPeriodic>(&solver_config.boundary_config.config)) {
                storage.ghost_handler.set(
                    GhostHandle{
                        scheduler(),
                        BCShearingPeriodic{
                            c->shear_base, c->shear_dir, c->shear_speed * time_val, c->shear_speed},
                        storage.patch_rank_owner,
                        storage.xyzh_ghost_layout});
            }
        }
        inline void reset_ghost_handler() { storage.ghost_handler.reset(); }

        void build_ghost_cache();
        void clear_ghost_cache();

        void merge_position_ghost();
 
        // trees
        using RTree = typename Config::RTree;
        void build_merged_pos_trees();
        void clear_merged_pos_trees();

        void compute_presteps_rint();
        void reset_presteps_rint();

        void start_neighbors_cache();
        void reset_neighbors_cache();

        void sph_prestep(Tscal time_val, Tscal dt);

        void apply_position_boundary(Tscal time_val);

        void update_artificial_viscosity(Tscal dt);

        void init_ghost_layout();

        void communicate_merge_ghosts_fields();
        void reset_merge_ghosts_fields();

        void compute_eos_fields();

        void reset_eos_fields();

        void prepare_corrector();
        void update_derivs(Tscal dt_hydro);
        bool apply_corrector(Tscal dt, u64 Npart_all);

        void update_sync_load_values();
 
        Solver(ShamrockCtx &context) : context(context) {}

        void init_solver_graph();

        void vtk_do_dump(std::string filename, bool add_patch_world_id);
 
        void set_debug_dump(bool _do_debug_dump, std::string _debug_dump_filename) {
            solver_config.set_debug_dump(_do_debug_dump, _debug_dump_filename);
        }
 
        inline void print_timestep_logs() {
            if (shamcomm::world_rank() == 0) {
                logger::info_ln("SPH", "iteration since start :", solve_logs.get_iteration_count());
                logger::info_ln("SPH", "time since start :", shambase::details::get_wtime(), "(s)");
            }
        }

        TimestepLog evolve_once();

        Tscal evolve_once_time_expl(Tscal t_current, Tscal dt_input) {
            solver_config.set_time(t_current);
            solver_config.set_next_dt(dt_input);
            evolve_once();
            return solver_config.get_dt_sph();
        }
 
        inline EvolveUntilResults evolve_until(
            Tscal target_time, i32 niter_max, f64 max_walltime = -1) {
 
            const bool niter_limit_active    = (niter_max >= 0);
            const bool walltime_limit_active = (max_walltime >= 0);
 
            if (shamcomm::world_rank() == 0) {
                logger::info_ln(
                    "SPH",
                    shambase::format(
                        "evolve_until (target_time = {:.2f}s, niter_max = {}, max_walltime = "
                        "{:.2f}s)",
                        target_time,
                        niter_max,
                        max_walltime));
            }
 
            auto synced_wtime = [&]() -> f64 {
                if (walltime_limit_active) {
                    return shamalgs::collective::allreduce_max(shambase::details::get_wtime());
                }
                return 0;
            };
 
            auto step = [&]() {
                Tscal dt = solver_config.get_dt_sph();
                Tscal t  = solver_config.get_time();
 
                if (t > target_time) {
                    throw shambase::make_except_with_loc<std::invalid_argument>(
                        "the target time is higher than the current time");
                }
 
                if (t + dt > target_time) {
                    solver_config.set_next_dt(target_time - t);
                }
                evolve_once();
            };
 
            f64 start_wall_time = (walltime_limit_active) ? synced_wtime() : 0;
 
            i32 next_walltime_check_iter
                = walltime_limit_active ? 1 : std::numeric_limits<i32>::max();
 
            i32 iter_count = 0;
 
            while (solver_config.get_time() < target_time) {
                step();
                iter_count++;
 
                // if the iteration count is greater than the maximum iteration count
                if (niter_limit_active && iter_count >= niter_max) {
                    if (shamcomm::world_rank() == 0) {
                        logger::info_ln(
                            "SPH", "stopping evolve until because of niter =", iter_count);
                    }
                    return {
                        .reach_target_time  = false,
                        .reach_niter_max    = true,
                        .reach_max_walltime = false,
                        .iter_count         = iter_count,
                    };
                }
 
                // if walltime limit is active and the next walltime check is due
                if (walltime_limit_active && iter_count >= next_walltime_check_iter) {
                    f64 global_walltime = synced_wtime();
 
                    // if the global walltime is greater than the max walltime
                    if (global_walltime >= max_walltime) {
                        if (shamcomm::world_rank() == 0) {
                            logger::info_ln(
                                "SPH",
                                shambase::format(
                                    "stopping evolve until because of "
                                    "max_walltime = {:.2f}s > {:.2f}s",
                                    global_walltime,
                                    max_walltime));
                        }
                        return {
                            .reach_target_time  = false,
                            .reach_niter_max    = false,
                            .reach_max_walltime = true,
                            .iter_count         = iter_count,
                        };
                    }
 
                    f64 sec_per_iter
                        = (global_walltime - start_wall_time) / static_cast<f64>(iter_count);
 
                    auto get_remaining_iters = [&](f64 delta_walltime, f64 factor) -> i32 {
                        if (sec_per_iter > 0) {
                            f64 tmp = factor * delta_walltime / sec_per_iter;
                            if (tmp > std::numeric_limits<i32>::max()) {
                                return std::numeric_limits<i32>::max();
                            }
                            return static_cast<i32>(tmp);
                        }
                        return 1000; // default to 1000 iterations if sec_per_iter is 0
                    };
 
                    i32 iters_to_limit = get_remaining_iters(max_walltime - global_walltime, 0.25);
                    i32 iters_to_next_check = iters_to_limit;
 
                    next_walltime_check_iter = iter_count + std::max(1, iters_to_next_check);
 
                    if (shamcomm::world_rank() == 0) {
                        logger::info_ln(
                            "SPH",
                            shambase::format(
                                "next walltime check in {:.2f}s (niter = {}) global walltime = "
                                "{:.2f}s (max_walltime = {:.2f}s)",
                                iters_to_next_check * sec_per_iter,
                                iters_to_next_check,
                                global_walltime,
                                max_walltime));
                    }
                }
            }
 
            print_timestep_logs();
 
            return {
                .reach_target_time  = true,
                .reach_niter_max    = false,
                .reach_max_walltime = false,
                .iter_count         = iter_count,
            };
        }
    };
 
} // namespace shammodels::sph