190 lines
6 KiB
C++
190 lines
6 KiB
C++
#pragma once
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#include "buffer.hpp"
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#include "config.hpp"
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#include "reader.hpp"
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#include "writer.hpp"
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#include <exception>
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#include <fstream>
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#include <queue>
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#include <stdexcept>
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#include <string>
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// returns amount of records read
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size_t read_chunk(Reader& reader, SubBuffer& buff)
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{
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for (size_t i = 0; i < buff.size(); i++) {
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std::optional<Record> in = reader.read();
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if (!in.has_value()) {
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return i;
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}
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buff[i] = in.value();
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}
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return buff.size();
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}
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void write_to_file(const std::string& filename, SubBuffer& buff, size_t n)
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{
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std::filesystem::path dirPath = std::filesystem::path(filename).parent_path();
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std::filesystem::create_directories(dirPath);
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std::ofstream out_stream(filename);
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Writer output_writer(out_stream);
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for (size_t j = 0; j < n; j++) {
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output_writer.write(buff[j]);
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}
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}
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size_t create_initial_runs(const std::string& input_filename, const std::string& directory, Buffer& main_buffer)
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{
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auto buff = main_buffer.divide(1)[0];
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std::ifstream in_stream(input_filename);
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Reader input_reader(in_stream);
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size_t run_index;
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for (run_index = 0;; run_index++) {
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size_t size = read_chunk(input_reader, buff);
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if (size == 0) {
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break;
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}
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std::sort(buff.begin(), buff.begin() + size);
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write_to_file(directory + "/" + std::to_string(run_index) + ".run", buff, size);
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}
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return run_index;
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}
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void write_block(Writer& w, SubBuffer& buff, size_t n)
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{
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for (size_t i = 0; i < n; i++) {
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w.write(buff[i]);
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}
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}
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void k_way_merge_and_write(std::vector<Reader>& input_readers, Writer& output_writer, std::vector<SubBuffer>& buffers)
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{
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// for debug purposes
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std::cout << "buffers size: " << buffers.size() << " input_readers: " << input_readers.size() << '\n';
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for (size_t i = 0; i < input_readers.size(); i++) {
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std::cout << "reader " << i << ": " << input_readers[i].read().value() << '\n';
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}
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struct HeapElement {
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Record record;
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size_t source_index;
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// priority queue is a max heap by default, so comparison is backwards
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bool operator<(const HeapElement& other) const
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{
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return !(record < other.record);
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}
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};
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using MinHeap = std::priority_queue<HeapElement>;
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MinHeap pq;
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struct BufferState {
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size_t items_total = 0;
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size_t current_idx = 0;
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};
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std::vector<BufferState> buffer_states(input_readers.size());
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// initial fill
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for (size_t i = 0; i < input_readers.size(); i++) {
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SubBuffer& input_buffer = buffers[i];
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buffer_states[i].items_total = read_chunk(input_readers[i], input_buffer);
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buffer_states[i].current_idx = 0;
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if (buffer_states[i].items_total == 0) {
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continue;
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}
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pq.push({ input_buffer[0], i });
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buffer_states[i].current_idx++;
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}
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size_t output_index = 0;
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SubBuffer& output_buffer = buffers[buffers.size() - 1];
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while (!pq.empty()) {
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HeapElement next = pq.top();
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pq.pop();
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output_buffer[output_index] = next.record;
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output_index++;
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if (output_index == output_buffer.size()) {
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write_block(output_writer, output_buffer, output_index);
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output_index = 0;
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}
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size_t source_index = next.source_index;
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if (buffer_states[source_index].current_idx >= buffer_states[source_index].items_total) {
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buffer_states[source_index].items_total = read_chunk(input_readers[source_index], buffers[source_index]);
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buffer_states[source_index].current_idx = 0;
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if (buffer_states[source_index].items_total == 0) {
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continue;
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}
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}
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pq.push({ buffers[source_index][buffer_states[source_index].current_idx], source_index });
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buffer_states[source_index].current_idx++;
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}
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}
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// I think more or less works correctly now
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// creates input readers, and output writer for a merge to be performed by another function
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// if not every file can be processed at once, splits them
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size_t run_merge_pass(std::vector<SubBuffer>& buffers, std::string current_dir, std::string next_dir, size_t file_count)
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{
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const size_t K = buffers.size() - 1; // Merge factor (e.g., 3)
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size_t new_runs = 0;
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for (size_t i = 0; i < file_count; i += K) {
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// std::cout << "pass 0 run " << i << '\n';
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// create input readers, to turn into a function i would have to some complicated ownership semantics, and i don't want to bother with that
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std::vector<std::ifstream> in_streams;
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std::vector<Reader> input_readers;
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in_streams.reserve(K);
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input_readers.reserve(K);
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for (size_t j = 0; j < K; j++) {
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std::string filename = current_dir + "/" + std::to_string(i + j) + ".run";
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in_streams.emplace_back(std::ifstream(filename));
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input_readers.emplace_back(Reader(in_streams[j]));
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}
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// create the output writer -||-
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std::string filename = next_dir + "/" + std::to_string(new_runs) + ".run";
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std::filesystem::path dirPath = std::filesystem::path(filename).parent_path();
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std::filesystem::create_directories(dirPath);
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std::ofstream out_stream(filename);
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Writer output_writer(out_stream);
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k_way_merge_and_write(input_readers, output_writer, buffers);
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new_runs++;
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}
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return new_runs;
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}
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int sort_file(const Configuration& opts)
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{
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Buffer main_buffer(opts.n * opts.b);
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size_t file_count;
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file_count = create_initial_runs(opts.input_file, opts.directory + "/pass0", main_buffer);
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auto buffers = main_buffer.divide(opts.n);
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for (int i = 0;; i++) {
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std::string current_dir = opts.directory + "/pass" + std::to_string(i);
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std::string next_dir = opts.directory + "/pass" + std::to_string(i + 1);
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file_count = run_merge_pass(buffers, current_dir, next_dir, file_count);
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if (file_count == 1) {
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// #todo move the resulting file to the output dir
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break;
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}
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}
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// #todo cleanup tmp files
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return 0;
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}
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