C++ emhash7::HashMap demonstration

llil4emh.cc

// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
// llil4emh.cc
// An emhash6::HashMap demonstration.
// https://www.perlmonks.com/?node_id=11149643
//
// April 25, 2024
//    Based on llil3m.cpp  https://perlmonks.com/?node_id=11149482
//    Original challenge   https://perlmonks.com/?node_id=11147822
//         and summary     https://perlmonks.com/?node_id=11150293
//    Other demonstrations https://perlmonks.com/?node_id=11149907
//
// Authors
//    Mario Roy - C++ demonstration with parallel capabilities
//    eyepopslikeamosquito - Co-author, learning C++ at PerlMonks.com
//
// See also, memory efficient variant
//    https://gist.github.com/marioroy/d02881b96b20fa1adde4388b3e216163
//
// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
// OpenMP Little Book - https://nanxiao.gitbooks.io/openmp-little-book
//
// Obtain the emhash hashmap library (required dependency):
//    git clone --depth=1 https://github.com/ktprime/emhash
//
// Compile on Linux (clang++ or g++):
//    clang++ -o llil4emh -std=c++20 -fopenmp -Wall -O3 llil4emh.cc
//
// On macOS, use g++-12 from https://brew.sh (installation: brew install gcc@12).
// The g++ command also works with mingw C++ compiler (https://sourceforge.net/projects/mingw-w64)
// that comes bundled with Strawberry Perl (C:\Strawberry\c\bin\g++.exe).
//
// Obtain gen-llil.pl and gen-long-llil.pl from https://perlmonks.com/?node_id=11148681
//    perl gen-llil.pl big1.txt 200 3 1
//    perl gen-llil.pl big2.txt 200 3 1
//    perl gen-llil.pl big3.txt 200 3 1
//
// To make random input, obtain shuffle.pl from https://perlmonks.com/?node_id=11149800
//    perl shuffle.pl big1.txt >tmp && mv tmp big1.txt
//    perl shuffle.pl big2.txt >tmp && mv tmp big2.txt
//    perl shuffle.pl big3.txt >tmp && mv tmp big3.txt
//
// Example run:  llil4emh big1.txt big2.txt big3.txt >out.txt
// NUM_THREADS=3 llil4emh ...
// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

#include <cassert>
#include <cstdio>
#include <cstddef>
#include <cstdint>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <compare>
#include <chrono>

#include <string>
#include <string_view>

#include <array>
#include <vector>

#include <thread>
#include <execution>
#include <atomic>

#include <iomanip>
#include <iostream>
#include <fstream>

#if defined(__GNUC__) && !defined(__clang__)
   #pragma GCC diagnostic push
   #pragma GCC diagnostic ignored "-Wunused-but-set-variable"
   #pragma GCC diagnostic ignored "-Wclass-memaccess"
   #include "emhash/hash_table6.hpp"
   #pragma GCC diagnostic pop
#else
   #include "emhash/hash_table6.hpp"
#endif

static_assert(sizeof(size_t) == sizeof(int64_t), "size_t too small, need a 64-bit compile");

// Specify 0/1 to use boost's parallel sorting algorithm; faster than __gnu_parallel::sort.
// https://www.boost.org/doc/libs/1_85_0/libs/sort/doc/html/sort/parallel.html
// https://www.boost.org/doc/libs/1_85_0/libs/sort/doc/papers/block_indirect_sort_en.pdf
// This requires the boost header files: e.g. devpkg-boost bundle on Clear Linux.
// Note: Another option is downloading and unpacking Boost locally.
// (no need to build it because the bits we use are header file only)
#define USE_BOOST_PARALLEL_SORT 1

#if USE_BOOST_PARALLEL_SORT
   #ifdef __clang__
      #pragma clang diagnostic push
      #pragma clang diagnostic ignored "-Wunused-parameter"
      #pragma clang diagnostic ignored "-Wshadow"
      #include <boost/sort/sort.hpp>
      #pragma clang diagnostic pop
   #else
      #include <boost/sort/sort.hpp>
   #endif
#endif

#ifdef _OPENMP
   #include <omp.h>
#endif

class spinlock_mutex {
// https://rigtorp.se/spinlock/
// https://vorbrodt.blog/2019/02/12/fast-mutex/
public:
   // Assignment is disabled.
   spinlock_mutex& operator=(const spinlock_mutex& rhs) = delete;

   void lock() noexcept {
      for (;;) {
         if (!lock_.exchange(true, std::memory_order_acquire))
            break;
         while (lock_.load(std::memory_order_relaxed))
            __builtin_ia32_pause();
      }
   }

   void unlock() noexcept {
      lock_.store(false, std::memory_order_release);
   }

private:
   alignas(4 * sizeof(std::max_align_t)) std::atomic_bool lock_ = false;
};

// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

typedef uint32_t int_type;

// All words in big1.txt, big2.txt, big3.txt are <= 6 chars in length.
// big.txt  max word length is 6
// long.txt max word length is 208
//
// Based on rough benchmarking, the short fixed string hack below is only
// worth trying for MAX_STR_LEN_L up to about 30.
// See also https://backlinko.com/google-keyword-study
//
// To use (limited length) fixed length strings uncomment the next line.
#define MAX_STR_LEN_L (size_t) 12

#ifdef MAX_STR_LEN_L
using hash_type = uint32_t;
struct str_type : std::array<char, MAX_STR_LEN_L> {
   bool operator==( const str_type& o ) const {
      return ::memcmp(this->data(), o.data(), MAX_STR_LEN_L) == 0;
   }
   bool operator<( const str_type& o ) const {
      return ::memcmp(this->data(), o.data(), MAX_STR_LEN_L) < 0;
   }
};
// inject specialization of std::hash for str_type into namespace std
namespace std {
   template<> struct hash<str_type> {
      std::size_t operator()( str_type const& v ) const noexcept {
         std::basic_string_view<char> bv {
            reinterpret_cast<const char*>(v.data()), v.size() * sizeof(char) };
         return (hash_type) std::hash<std::basic_string_view<char>>()(bv);
      }
   };
}
#else
using hash_type        = uint64_t;
using str_type         = std::basic_string<char>;
#endif

using str_int_type     = std::pair<str_type, int_type>;
using vec_str_int_type = std::vector<str_int_type>;

struct Key {
   hash_type hash;
   str_type  name;
};

using map_str_int_type = emhash6::HashMap<
   Key, int_type,
   decltype( [](const Key& k) { return k.hash; } ),
   decltype( [](const Key& l, const Key& r) { return l.name == r.name; } )
>;

// Mimic the Perl get_properties subroutine ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

// convert positive number from string to uint32_t
inline uint32_t fast_atoll64(const char* str)
{
   uint32_t val = 0;
   uint8_t digit;
   while ((digit = uint8_t(*str++ - '0')) <= 9)
      val = val * 10 + digit;
   return val;
}

// Helper function to find a character.
inline char* find_char(char* first, char* last, char c)
{
   while (first != last) {
      if (*first == c) break;
      ++first;
   }
   return first;
}

// Limit chunk size and line length.
inline constexpr size_t CHUNK_SIZE   = 32768;
inline constexpr size_t MAX_LINE_LEN = 255;
inline constexpr size_t NUM_MAPS     = 1 << 12;

static int64_t get_properties(
   const char*        fname,     // in    : the input file name
   const int          nthds,     // in    : the number of threads
   auto&              L,         // in    : the locks array
   auto&              M)         // inout : the maps array
{
   int64_t num_lines = 0;
   std::ifstream fin(fname, std::ifstream::binary);
   if (!fin.is_open()) {
      std::cerr << "Error opening '" << fname << "' : " << strerror(errno) << '\n';
      return num_lines;
   }

   #pragma omp parallel reduction(+:num_lines)
   {
      std::string buf;
      buf.resize(CHUNK_SIZE + MAX_LINE_LEN + 1, '\0');

      while (fin.good()) {
         size_t len = 0;

         // Read the next chunk serially.
         #pragma omp critical
         {
            fin.read(&buf[0], CHUNK_SIZE);
            if ((len = fin.gcount()) > 0) {
               if (buf[len - 1] != '\n' && fin.getline(&buf[len], MAX_LINE_LEN)) {
                  // Getline discards the newline char and appends null char.
                  // Therefore, change '\0' to '\n'.
                  len += fin.gcount();
                  buf[len - 1] = '\n';
               }
            }
         }

         if (!len)
            break;

         buf[len]    = '\0';
         char *first = &buf[0];
         char *last  = &buf[len];

         // Process max Nthreads chunks concurrently.
         while (first < last) {
            char* beg_ptr{first};
            char* end_ptr{find_char(first, last, '\n')};
            char* found = find_char(beg_ptr, end_ptr, '\t');

            first = end_ptr + 1;
            if (found == end_ptr)
               continue;

            assert(*found == '\t');
            int_type count = fast_atoll64(found + 1);
            size_t klen = found - beg_ptr;

#ifdef MAX_STR_LEN_L
            str_type s {};  // {} initializes all elements of s to '\0'
            ::memcpy(s.data(), beg_ptr, std::min(MAX_STR_LEN_L, klen));
#else
            str_type s(beg_ptr, klen);
#endif
            hash_type hv = (hash_type) std::hash<std::basic_string_view<char>>{}(
               std::basic_string_view<char>{ reinterpret_cast<const char*>(s.data()), klen });

            if (nthds == 1) {
               auto [it, success] = M[0].try_emplace(Key{ hv, std::move(s) }, count);
               if (!success) it->second += count;
            }
            else {
               size_t idx = ( ((hv & 0x000000000000ffffULL) << 16) |
                              ((hv & 0x00000000ffff0000ULL) >> 16) ) % NUM_MAPS;

               L[idx].lock();
               auto [it, success] = M[idx].try_emplace(Key{ hv, std::move(s) }, count);
               if (!success) it->second += count;
               L[idx].unlock();
            }

            ++num_lines;
         }
      }
   }

   fin.close();
   // std::cerr << "getprops done\n";
   return num_lines;
}

// Output subroutine ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

size_t divide_up(size_t dividend, size_t divisor)
{
   if (dividend % divisor)
      return (size_t)(dividend / divisor) + 1;
   else
      return (size_t)(dividend / divisor);
}

static void out_properties(
   const int          nthds,     // in   : the number of threads
   vec_str_int_type&  vec)       // in   : the vector to output
{
   size_t num_chunks = divide_up(vec.size(), CHUNK_SIZE);
   int nthds_out = 1;
#ifdef _OPENMP
   nthds_out = std::min(nthds, 32);
#endif

   #pragma omp parallel for ordered schedule(static, 1) num_threads(nthds_out)
   for (size_t chunk_id = 1; chunk_id <= num_chunks; ++chunk_id) {
      std::string str(""); str.reserve(2048 * 1024);
      auto it  = vec.begin() + (chunk_id - 1) * CHUNK_SIZE;
      auto it2 = vec.begin() + std::min(vec.size(), chunk_id * CHUNK_SIZE);

      for (; it != it2; ++it) {
#ifdef MAX_STR_LEN_L
         str.append(it->first.data());
#else
         str.append(it->first.data(), it->first.size());
#endif
         str.append("\t", 1);
         str.append(std::to_string(it->second));
         str.append("\n", 1);
      }

      #pragma omp ordered
      std::cout << str << std::flush;
   }
}

typedef std::chrono::high_resolution_clock high_resolution_clock;
typedef std::chrono::high_resolution_clock::time_point time_point;
typedef std::chrono::milliseconds milliseconds;

double elaspe_time(time_point cend, time_point cstart) {
   return double (
      std::chrono::duration_cast<milliseconds>(cend - cstart).count()
   ) * 1e-3;
}

// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

int main(int argc, char* argv[])
{
   if (argc < 2) {
      if (argc > 0)
         std::cerr << "usage: llil4emh file1 file2 ... >out.txt\n";
      return 1;
   }

   std::cerr << std::setprecision(3) << std::setiosflags(std::ios::fixed);
#ifdef MAX_STR_LEN_L
   std::cerr << "llil4emh (fixed string length=" << MAX_STR_LEN_L << ") start\n";
#else
   std::cerr << "llil4emh start\n";
#endif
#ifdef _OPENMP
   std::cerr << "use OpenMP\n";
#else
   std::cerr << "don't use OpenMP\n";
#endif
#if USE_BOOST_PARALLEL_SORT == 0
   std::cerr << "don't use boost sort\n";
#else
   std::cerr << "use boost sort\n";
#endif
   time_point cstart1, cend1, cstart2, cend2, cstart3, cend3s, cend3;
   cstart1 = high_resolution_clock::now();

#ifdef _OPENMP
   // Determine the number of threads.
   const char* env_nthds = std::getenv("NUM_THREADS");
   int nthds = ( env_nthds && strlen(env_nthds) )
      ? ::atoi(env_nthds)
      : std::thread::hardware_concurrency();
   omp_set_dynamic(false);
   omp_set_num_threads(nthds);
   omp_set_max_active_levels(1);
   int nthds_move = std::min(nthds, 12);
#else
   int nthds = 1;
   int nthds_move = 1;
#endif

   // Get the list of input files from the command line
   int    nfiles = argc - 1;
   char** fname  = &argv[1];

   // Store the properties into a vector
   vec_str_int_type propvec;
   int64_t num_lines = 0;
   int64_t num_keys = 0;

   {
      // Enclose shared vars L and M inside a block, for running parallel.
      // So GC releases the objects immediately after exiting the scope.
      spinlock_mutex    L[NUM_MAPS];
      map_str_int_type  M[NUM_MAPS];

      for (int i = 0; i < nfiles; ++i)
         num_lines += get_properties(fname[i], nthds, L, M);

      for (size_t i = 0; i < NUM_MAPS; ++i)
         num_keys += M[i].size();

      cend1 = high_resolution_clock::now();
      double ctaken1 = elaspe_time(cend1, cstart1);
      std::cerr << "get properties      " << std::setw(8) << ctaken1 << " secs\n";

      if (num_keys == 0) {
         std::cerr << "No work, exiting...\n";
         return 1;
      }

      cstart2 = high_resolution_clock::now();

      if (nthds == 1) {
         propvec.reserve(num_keys);
         for (auto const& x : M[0])
            propvec.emplace_back(std::move(x.first.name), x.second);

         // emhash's clear() retains capacity until out of scope
         // swap map with an empty temporary, which is immediately destroyed
         // M[0].clear();
         map_str_int_type().swap(M[0]);
      }
      else {
         propvec.resize(num_keys);
         std::array<vec_str_int_type::iterator, NUM_MAPS> I;
         I[0] = propvec.begin();

         for (size_t i = 1; i < NUM_MAPS; ++i)
            I[i] = I[i-1] + M[i-1].size();

         #pragma omp parallel for schedule(static, 1) num_threads(nthds_move)
         for (size_t i = 0; i < NUM_MAPS; ++i) {
            auto it = I[i];
            for (auto const& x : M[i])
               *it++ = std::make_pair(std::move(x.first.name), x.second);

            // M[i].clear();
            map_str_int_type().swap(M[i]);
         }
      }

      cend2 = high_resolution_clock::now();
      double ctaken2 = elaspe_time(cend2, cstart2);
      std::cerr << "map to vector       " << std::setw(8) << ctaken2 << " secs\n";
   }

   cstart3 = high_resolution_clock::now();

   // Sort the vector by (count) in reverse order, (name) in lexical order
   auto reverse_order = [](const str_int_type& left, const str_int_type& right) {
      return left.second != right.second
         ? left.second > right.second
         : left.first  < right.first;
   };
#if USE_BOOST_PARALLEL_SORT == 0
   // Standard sort
   std::sort(propvec.begin(), propvec.end(), reverse_order);
#else
   // Parallel sort
   boost::sort::block_indirect_sort(
      propvec.begin(), propvec.end(), reverse_order,
   #ifdef __NVCOMPILER_LLVM__
      std::min(nthds, 32)
   #else
      nthds
   #endif
   );
#endif

   cend3s = high_resolution_clock::now();

   // Output the sorted vector
   out_properties(nthds, propvec);
   cend3 = high_resolution_clock::now();

   double ctaken   = elaspe_time(cend3, cstart1);
   double ctaken3s = elaspe_time(cend3s, cstart3);
   double ctaken3o = elaspe_time(cend3, cend3s);

   std::cerr << "vector stable sort  " << std::setw(8) << ctaken3s << " secs\n";
   std::cerr << "write stdout        " << std::setw(8) << ctaken3o << " secs\n";
   std::cerr << "total time          " << std::setw(8) << ctaken   << " secs\n";
   std::cerr << "    count lines     " << num_lines << "\n";
   std::cerr << "    count unique    " << propvec.size() << "\n";

   // Hack to see Private Bytes in Windows Task Manager
   // (uncomment next line so process doesn't exit too quickly)
   // std::this_thread::sleep_for(milliseconds(9000));

   return 0;
}