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C++ phmap::flat_hash_map demonstration
// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
// llil4hmap.cc
// https://www.perlmonks.com/?node_id=11149643
// A phmap::flat_hash_map demonstration.
// By Mario Roy, April 7, 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
// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
// OpenMP Little Book - https://nanxiao.gitbooks.io/openmp-little-book
//
// Obtain the parallel hashmap library (required dependency):
// git clone --depth=1 https://github.com/greg7mdp/parallel-hashmap
//
// Compile on Linux (clang++ or g++):
// clang++ -o llil4hmap -std=c++20 -fopenmp -Wall -O3 llil4hmap.cc -I./parallel-hashmap
//
// 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
// perl gen-long-llil.pl long1.txt 600
// perl gen-long-llil.pl long2.txt 600
// perl gen-long-llil.pl long3.txt 600
//
// 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: llil4hmap big1.txt big2.txt big3.txt >out.txt
// NUM_THREADS=3 llil4hmap ...
// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
#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>
#include <parallel_hashmap/phmap.h>
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_81_0/libs/sort/doc/html/sort/parallel.html
// 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 = phmap::flat_hash_map<
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 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
// fast_atoll64
// https://stackoverflow.com/questions/16826422/
// c-most-efficient-way-to-convert-string-to-int-faster-than-atoi
// convert positive number from string to uint32_t
inline uint32_t fast_atoll64(const char* str)
{
uint32_t val = 0;
// int sign = 0;
// if (*str == '-') {
// sign = 1, ++str;
// }
uint8_t digit;
while ((digit = uint8_t(*str++ - '0')) <= 9)
val = val * 10 + digit;
// return sign ? -val : val;
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');
char *first, *last, *found;
size_t len, klen, idx;
int_type count;
hash_type hv;
while (fin.good()) {
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';
first = &buf[0];
last = &buf[len];
// Process max Nthreads chunks concurrently.
while (first < last) {
char* beg_ptr{first}; first = find_char(first, last, '\n');
char* end_ptr{first}; ++first, ++num_lines;
if ((found = find_char(beg_ptr, end_ptr, '\t')) == end_ptr) continue;
count = fast_atoll64(found + 1);
#ifdef MAX_STR_LEN_L
str_type s {}; // {} initializes all elements of s to '\0'
klen = std::min(MAX_STR_LEN_L, (size_t)(found - beg_ptr));
::memcpy(s.data(), beg_ptr, klen);
#else
klen = found - beg_ptr;
str_type s(beg_ptr, klen);
#endif
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 {
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();
}
}
}
}
fin.close();
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: llil4hmap file1 file2 ... >out.txt\n";
return 1;
}
std::cerr << std::setprecision(3) << std::setiosflags(std::ios::fixed);
#ifdef MAX_STR_LEN_L
std::cerr << "llil4hmap (fixed string length=" << MAX_STR_LEN_L << ") start\n";
#else
std::cerr << "llil4hmap 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);
// phmap'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;
}
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