memory_projection.cpp

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// SPDX-License-Identifier: GPL-2.0-only
//
// Copyright (c) 2026-present FERS Contributors (see AUTHORS.md).
//
// See the GNU GPLv2 LICENSE file in the FERS project root for more information.
 
#include "memory_projection.h"
 
#include <algorithm>
#include <array>
#include <cmath>
#include <cstdint>
#include <format>
#include <fstream>
#include <limits>
#include <nlohmann/json.hpp>
#include <optional>
#include <string>
#include <unordered_map>
 
#if defined(__APPLE__) && defined(__MACH__)
#include <mach/mach.h>
#elif defined(__linux__)
#include <unistd.h>
#endif
 
#include "core/logging.h"
#include "core/parameters.h"
#include "core/sim_id.h"
#include "core/world.h"
#include "radar/receiver.h"
#include "radar/transmitter.h"
#include "timing/timing.h"
 
namespace core
{
    namespace
    {
        using radar::OperationMode;
 
        constexpr std::uint64_t max_uint64 = std::numeric_limits<std::uint64_t>::max(); ///< Saturating byte-count cap.
 
        /**
         * @brief Checks whether a receiver emits sample-by-sample streaming output.
         * @param receiver The receiver to inspect.
         * @return True for CW and FMCW receivers, false otherwise.
         */
        [[nodiscard]] bool isStreamingReceiver(const radar::Receiver& receiver) noexcept
        {
            return receiver.getMode() == OperationMode::CW_MODE || receiver.getMode() == OperationMode::FMCW_MODE ||
                receiver.getMode() == OperationMode::SFCW_MODE;
        }
 
        /**
         * @brief Converts a finite floating-point count to an integer by rounding up.
         * @param value The floating-point count to convert.
         * @param overflowed Set to true when the input cannot be represented as `uint64_t`.
         * @return The rounded-up count, clamped to `uint64_t` max on overflow.
         */
        [[nodiscard]] std::uint64_t ceilToUint64(const RealType value, bool& overflowed) noexcept
        {
            if (!std::isfinite(value))
            {
                overflowed = true;
                return max_uint64;
            }
            if (value <= 0.0)
            {
                return 0;
            }
            if (value >= static_cast<RealType>(max_uint64))
            {
                overflowed = true;
                return max_uint64;
            }
            const RealType nearest = std::round(value);
            const RealType tolerance = 1.0e-12 * std::max<RealType>(1.0, std::abs(nearest));
            if (std::abs(value - nearest) <= tolerance)
            {
                return static_cast<std::uint64_t>(nearest);
            }
            return static_cast<std::uint64_t>(std::ceil(value));
        }
 
        /**
         * @brief Adds two byte projections while preserving overflow state.
         * @param lhs The left-hand byte projection.
         * @param rhs The right-hand byte projection.
         * @return The summed projection, clamped to `uint64_t` max on overflow.
         */
        [[nodiscard]] ByteProjection addBytes(const ByteProjection lhs, const ByteProjection rhs) noexcept
        {
            ByteProjection result{};
            result.overflowed = lhs.overflowed || rhs.overflowed;
            if (max_uint64 - lhs.bytes < rhs.bytes)
            {
                result.bytes = max_uint64;
                result.overflowed = true;
                return result;
            }
            result.bytes = lhs.bytes + rhs.bytes;
            return result;
        }
 
        /**
         * @brief Multiplies two byte-count factors while preserving prior overflow state.
         * @param lhs The left-hand factor.
         * @param rhs The right-hand factor.
         * @param input_overflowed True if an upstream calculation has already overflowed.
         * @return The product projection, clamped to `uint64_t` max on overflow.
         */
        [[nodiscard]] ByteProjection multiplyBytes(const std::uint64_t lhs, const std::uint64_t rhs,
                                                   const bool input_overflowed = false) noexcept
        {
            ByteProjection result{};
            result.overflowed = input_overflowed;
            if (lhs != 0 && rhs > max_uint64 / lhs)
            {
                result.bytes = max_uint64;
                result.overflowed = true;
                return result;
            }
            result.bytes = lhs * rhs;
            return result;
        }
 
        /**
         * @brief Converts an oversampled sample count to the rendered output sample count.
         * @param oversampled_samples The sample count at the internal simulation rate.
         * @return The sample count after applying the configured oversample ratio.
         */
        [[nodiscard]] std::uint64_t downsampledSampleCount(const std::uint64_t oversampled_samples) noexcept
        {
            const unsigned ratio = params::oversampleRatio();
            if (ratio <= 1)
            {
                return oversampled_samples;
            }
            return oversampled_samples / ratio;
        }
 
        /**
         * @brief Counts samples required for a duration at a given sample rate.
         * @param duration_seconds Duration of the interval in seconds.
         * @param sample_rate_hz Sample rate used for the interval.
         * @param overflowed Set to true if the count cannot be represented as `uint64_t`.
         * @return The rounded-up sample count for the interval.
         */
        [[nodiscard]] std::uint64_t countSamplesForDuration(const RealType duration_seconds,
                                                            const RealType sample_rate_hz, bool& overflowed) noexcept
        {
            return ceilToUint64(duration_seconds * sample_rate_hz, overflowed);
        }
 
        /**
         * @brief Counts evenly spaced start times within an inclusive time range.
         * @param first_start First candidate start time.
         * @param last_start Last allowed start time.
         * @param step_seconds Spacing between successive starts.
         * @param overflowed Set to true if the count cannot be represented as `uint64_t`.
         * @return The number of starts in range, or zero for an invalid range.
         */
        [[nodiscard]] std::uint64_t countStartsInRange(const RealType first_start, const RealType last_start,
                                                       const RealType step_seconds, bool& overflowed) noexcept
        {
            if (first_start > last_start || step_seconds <= 0.0 || !std::isfinite(step_seconds))
            {
                return 0;
            }
            return ceilToUint64(std::floor((last_start - first_start) / step_seconds) + 1.0, overflowed);
        }
 
        /**
         * @brief Projects the number of receive windows emitted by a pulsed receiver.
         * @param receiver The pulsed receiver to inspect.
         * @param overflowed Set to true if any window count arithmetic overflows.
         * @return The projected number of receive windows during the simulation.
         */
        [[nodiscard]] std::uint64_t countPulsedWindows(const radar::Receiver& receiver, bool& overflowed)
        {
            const RealType prf = receiver.getWindowPrf();
            if (prf <= 0.0 || !std::isfinite(prf))
            {
                return 0;
            }
 
            const RealType sim_end = params::endTime();
            const RealType step_seconds = 1.0 / prf;
            const auto& schedule = receiver.getSchedule();
            std::uint64_t total = 0;
 
            if (schedule.empty())
            {
                const RealType first_start = receiver.getWindowStart(0);
                if (first_start >= sim_end)
                {
                    return 0;
                }
                const auto count = countStartsInRange(first_start, sim_end, step_seconds, overflowed);
                return count;
            }
 
            RealType next_requested = receiver.getWindowStart(0);
            bool counted_any_window = false;
            for (const auto& period : schedule)
            {
                const RealType period_end = std::min(period.end, sim_end);
                if (period_end < period.start || next_requested > period_end)
                {
                    continue;
                }
 
                const RealType first_start = std::max(next_requested, period.start);
                if (!counted_any_window && first_start >= sim_end)
                {
                    break;
                }
 
                const auto count = countStartsInRange(first_start, period_end, step_seconds, overflowed);
                if (count == 0)
                {
                    continue;
                }
 
                const auto added = addBytes({.bytes = total}, {.bytes = count});
                total = added.bytes;
                overflowed = overflowed || added.overflowed;
                counted_any_window = true;
                next_requested = first_start + static_cast<RealType>(count) * step_seconds;
            }
 
            return total;
        }
 
        /**
         * @brief Reads the process resident set size from the current platform when supported.
         * @return The current resident set size in bytes, or `std::nullopt` when unavailable.
         */
        [[nodiscard]] std::optional<std::uint64_t> currentResidentSetBytes() noexcept
        {
#if defined(__linux__)
            long const page_size = sysconf(_SC_PAGESIZE);
            if (page_size <= 0)
            {
                return std::nullopt;
            }
 
            std::ifstream statm("/proc/self/statm");
            if (!statm)
            {
                return std::nullopt;
            }
 
            std::string ignored_total_pages;
            unsigned long resident_pages = 0;
            statm >> ignored_total_pages >> resident_pages;
            if (!statm)
            {
                return std::nullopt;
            }
 
            const auto pages = static_cast<std::uint64_t>(resident_pages);
            const auto bytes = multiplyBytes(pages, static_cast<std::uint64_t>(page_size));
            if (bytes.overflowed)
            {
                return max_uint64;
            }
            return bytes.bytes;
#elif defined(__APPLE__) && defined(__MACH__)
            mach_task_basic_info_data_t info{};
            mach_msg_type_number_t count = MACH_TASK_BASIC_INFO_COUNT;
            if (task_info(mach_task_self(), MACH_TASK_BASIC_INFO, reinterpret_cast<task_info_t>(&info), &count) !=
                KERN_SUCCESS)
            {
                return std::nullopt;
            }
            return static_cast<std::uint64_t>(info.resident_size);
#else
            return std::nullopt;
#endif
        }
 
        /**
         * @brief Converts a byte projection to the JSON shape used by memory reports.
         * @param projection The byte projection to serialize.
         * @return A JSON object containing raw bytes, formatted bytes, and overflow state.
         */
        [[nodiscard]] nlohmann::json byteProjectionToJson(const ByteProjection projection)
        {
            return {{"bytes", projection.bytes},
                    {"human", formatByteSize(projection.bytes)},
                    {"overflowed", projection.overflowed}};
        }
 
        /**
         * @brief Converts an optional byte projection to JSON, preserving unknown values.
         * @param projection The optional byte projection to serialize.
         * @return A JSON object with nullable bytes when the projection is unavailable.
         */
        [[nodiscard]] nlohmann::json optionalByteProjectionToJson(const std::optional<ByteProjection>& projection)
        {
            if (!projection.has_value())
            {
                return {{"bytes", nullptr}, {"human", "unknown"}, {"overflowed", false}};
            }
            return byteProjectionToJson(*projection);
        }
    }
 
    std::vector<std::shared_ptr<timing::Timing>> collectCwPhaseNoiseTimings(const World& world)
    {
        std::unordered_map<SimId, std::shared_ptr<timing::Timing>> unique_timings;
 
        for (const auto& transmitter_ptr : world.getTransmitters())
        {
            if (!transmitter_ptr->isStreamingMode())
            {
                continue;
            }
            unique_timings.try_emplace(transmitter_ptr->getTiming()->getId(), transmitter_ptr->getTiming());
        }
 
        for (const auto& receiver_ptr : world.getReceivers())
        {
            if (!isStreamingReceiver(*receiver_ptr))
            {
                continue;
            }
            unique_timings.try_emplace(receiver_ptr->getTiming()->getId(), receiver_ptr->getTiming());
        }
 
        std::vector<std::shared_ptr<timing::Timing>> timings;
        timings.reserve(unique_timings.size());
        for (const auto& entry : unique_timings)
        {
            timings.push_back(entry.second);
        }
        return timings;
    }
 
    void addStreamingReceiverProjection(SimulationMemoryProjection& projection, const radar::Receiver& receiver,
                                        const bool sample_count_overflowed)
    {
        ++projection.streaming_receiver_count;
        bool if_count_overflowed = false;
        const auto if_sample_rate = receiver.getIfSampleRate();
        const bool if_rate_dechirped = receiver.isDechirpEnabled() && if_sample_rate.has_value();
        const auto if_sample_count = if_rate_dechirped
            ? countSamplesForDuration(projection.duration_seconds, if_sample_rate.value_or(0.0), if_count_overflowed)
            : std::uint64_t{0};
        const auto rendered_samples = if_rate_dechirped
            ? if_sample_count
            : (receiver.isDechirpEnabled() ? projection.streaming_sample_count
                                           : downsampledSampleCount(projection.streaming_sample_count));
        projection.rendered_hdf5_sample_count =
            addBytes({.bytes = projection.rendered_hdf5_sample_count},
                     {.bytes = rendered_samples, .overflowed = sample_count_overflowed || if_count_overflowed})
                .bytes;
        const auto resident_samples = if_rate_dechirped ? if_sample_count : projection.streaming_sample_count;
        projection.streaming_iq_buffers =
            addBytes(projection.streaming_iq_buffers,
                     multiplyBytes(resident_samples, static_cast<std::uint64_t>(sizeof(ComplexType)),
                                   sample_count_overflowed || if_count_overflowed));
    }
 
    void addPulsedReceiverProjection(SimulationMemoryProjection& projection, const radar::Receiver& receiver)
    {
        ++projection.pulsed_receiver_count;
        bool window_count_overflowed = false;
        const auto windows = countPulsedWindows(receiver, window_count_overflowed);
        projection.pulsed_window_count = addBytes({.bytes = projection.pulsed_window_count},
                                                  {.bytes = windows, .overflowed = window_count_overflowed})
                                             .bytes;
 
        bool pulsed_sample_count_overflowed = false;
        const auto raw_window_samples = countSamplesForDuration(
            receiver.getWindowLength(), projection.simulation_sample_rate_hz, pulsed_sample_count_overflowed);
        const auto rendered_window_samples = downsampledSampleCount(raw_window_samples);
        const auto rendered_samples =
            multiplyBytes(windows, rendered_window_samples, window_count_overflowed || pulsed_sample_count_overflowed);
        projection.rendered_hdf5_sample_count =
            addBytes({.bytes = projection.rendered_hdf5_sample_count}, rendered_samples).bytes;
    }
 
    SimulationMemoryProjection projectSimulationMemory(const World& world)
    {
        SimulationMemoryProjection projection{};
        projection.duration_seconds = std::max<RealType>(0.0, params::endTime() - params::startTime());
        projection.oversample_ratio = params::oversampleRatio();
        projection.simulation_sample_rate_hz = params::rate() * static_cast<RealType>(projection.oversample_ratio);
 
        bool sample_count_overflowed = false;
        projection.streaming_sample_count = countSamplesForDuration(
            projection.duration_seconds, projection.simulation_sample_rate_hz, sample_count_overflowed);
 
        const RealType phase_noise_lookup_start = world.earliestPhaseNoiseLookupStart();
        bool phase_noise_count_overflowed = false;
        projection.phase_noise_sample_count =
            countSamplesForDuration(std::max<RealType>(0.0, params::endTime() - phase_noise_lookup_start),
                                    projection.simulation_sample_rate_hz, phase_noise_count_overflowed);
        if (projection.phase_noise_sample_count != max_uint64)
        {
            ++projection.phase_noise_sample_count;
        }
        if (phase_noise_count_overflowed)
        {
            projection.phase_noise_sample_count = max_uint64;
        }
 
        const auto timings = collectCwPhaseNoiseTimings(world);
        projection.phase_noise_timing_count = static_cast<std::uint64_t>(timings.size());
        for (const auto& timing : timings)
        {
            if (timing && timing->isEnabled())
            {
                ++projection.enabled_phase_noise_timing_count;
            }
        }
 
        projection.phase_noise_lookup =
            multiplyBytes(projection.phase_noise_sample_count,
                          projection.enabled_phase_noise_timing_count * static_cast<std::uint64_t>(sizeof(RealType)),
                          sample_count_overflowed);
 
        for (const auto& receiver_ptr : world.getReceivers())
        {
            const auto& receiver = *receiver_ptr;
            if (isStreamingReceiver(receiver))
            {
                addStreamingReceiverProjection(projection, receiver, sample_count_overflowed);
                continue;
            }
 
            if (receiver.getMode() == OperationMode::PULSED_MODE)
            {
                addPulsedReceiverProjection(projection, receiver);
            }
        }
 
        projection.rendered_hdf5_payload =
            multiplyBytes(projection.rendered_hdf5_sample_count, 2ULL * static_cast<std::uint64_t>(sizeof(RealType)));
 
        projection.current_resident_set = currentResidentSetBytes();
        if (projection.current_resident_set.has_value())
        {
            projection.resident_baseline = ByteProjection{.bytes = *projection.current_resident_set};
            projection.projected_total_footprint =
                addBytes(addBytes(addBytes(projection.phase_noise_lookup, projection.streaming_iq_buffers),
                                  projection.rendered_hdf5_payload),
                         *projection.resident_baseline);
        }
 
        return projection;
    }
 
    std::string formatByteSize(const std::uint64_t bytes)
    {
        constexpr std::array units = {"B", "KiB", "MiB", "GiB", "TiB", "PiB", "EiB"};
        auto value = static_cast<long double>(bytes);
        std::size_t unit_index = 0;
        while (value >= 1024.0L && unit_index + 1 < units.size())
        {
            value /= 1024.0L;
            ++unit_index;
        }
        if (unit_index == 0)
        {
            return std::format("{} {}", bytes, units.at(unit_index));
        }
        return std::format("{:.2f} {}", static_cast<double>(value), units.at(unit_index));
    }
 
    std::string memoryProjectionToJsonString(const SimulationMemoryProjection& projection)
    {
        const nlohmann::json result = {
            {"duration_seconds", projection.duration_seconds},
            {"simulation_sample_rate_hz", projection.simulation_sample_rate_hz},
            {"oversample_ratio", projection.oversample_ratio},
            {"sample_counts",
             {{"streaming_samples", projection.streaming_sample_count},
              {"phase_noise_samples_per_enabled_timing", projection.phase_noise_sample_count},
              {"rendered_hdf5_samples", projection.rendered_hdf5_sample_count},
              {"pulsed_windows", projection.pulsed_window_count}}},
            {"object_counts",
             {{"phase_noise_timing_sources", projection.phase_noise_timing_count},
              {"enabled_phase_noise_timing_sources", projection.enabled_phase_noise_timing_count},
              {"streaming_receivers", projection.streaming_receiver_count},
              {"pulsed_receivers", projection.pulsed_receiver_count}}},
            {"phase_noise_lookups", byteProjectionToJson(projection.phase_noise_lookup)},
            {"streaming_iq_buffers", byteProjectionToJson(projection.streaming_iq_buffers)},
            {"rendered_hdf5_dataset_payload", byteProjectionToJson(projection.rendered_hdf5_payload)},
            {"current_resident_set",
             projection.current_resident_set.has_value()
                 ? nlohmann::json{{"bytes", *projection.current_resident_set},
                                  {"human", formatByteSize(*projection.current_resident_set)}}
                 : nlohmann::json{{"bytes", nullptr}, {"human", "unknown"}}},
            {"resident_baseline", optionalByteProjectionToJson(projection.resident_baseline)},
            {"projected_total_footprint", optionalByteProjectionToJson(projection.projected_total_footprint)}};
        return result.dump(2);
    }
 
    void logSimulationMemoryProjection(const World& world)
    {
        const auto projection = projectSimulationMemory(world);
        const std::string resident_baseline =
            projection.resident_baseline.has_value() ? formatByteSize(projection.resident_baseline->bytes) : "unknown";
        const std::string total = projection.projected_total_footprint.has_value()
            ? formatByteSize(projection.projected_total_footprint->bytes)
            : "unknown";
 
        LOG(logging::Level::DEBUG,
            "Projected simulation footprint: phase_noise_lookup_memory={} ({} enabled timing sources x {} samples), "
            "streaming_output_buffer_memory={} ({} streaming receivers, IF-rate receivers use IF sample counts), "
            "rendered_hdf5_dataset_payload={} "
            "({} output samples), resident_baseline={} (current RSS before projected run allocations), "
            "projected_total_footprint={}.",
            formatByteSize(projection.phase_noise_lookup.bytes), projection.enabled_phase_noise_timing_count,
            projection.phase_noise_sample_count, formatByteSize(projection.streaming_iq_buffers.bytes),
            projection.streaming_receiver_count, formatByteSize(projection.rendered_hdf5_payload.bytes),
            projection.rendered_hdf5_sample_count, resident_baseline, total);
 
        constexpr std::uint64_t one_gib = 1024ULL * 1024ULL * 1024ULL;
        for (const auto& receiver_ptr : world.getReceivers())
        {
            const auto& receiver = *receiver_ptr;
            if (!receiver.isDechirpEnabled())
            {
                continue;
            }
            if (receiver.hasFmcwIfSampleRate())
            {
                continue;
            }
            const auto projected_payload =
                multiplyBytes(projection.streaming_sample_count, 2ULL * static_cast<std::uint64_t>(sizeof(RealType)));
            if (projected_payload.bytes > one_gib || projected_payload.overflowed)
            {
                const auto gib = static_cast<long double>(projected_payload.bytes) / static_cast<long double>(one_gib);
                // TODO: UI workflows should have disk+memory usage stats on the SimulationView page (shows before user
                // runs the sim)
                LOG(logging::Level::WARNING,
                    "Receiver {} is outputting RF-rate IF data. Projected file size is {:.2f} GiB. This is expected "
                    "for V1 native dechirping, but ensure you have sufficient disk space. Future versions will support "
                    "IF-rate decimation.",
                    receiver.getName(), static_cast<double>(gib));
            }
        }
    }
}