cpp-taskflow/example/threadpool.cpp at master · WhyBingo/cpp-taskflow · GitHub

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// 2018/12/08 modified by Tsung-Wei Huang

// - refactored the output format

// 2018/12/07 modified by Tsung-Wei Huang

// - refactored the output format

// 2018/12/06 modified by Tsung-Wei Huang

// - added nested insertions test

// 2018/12/04 modified by Tsung-Wei Huang

// - replace privatized threadpool with work stealing threadpool

// 2018/10/04 modified by Tsung-Wei Huang

// - removed binary_tree

// - removed modulo_insertions

// - adopted to the new threadpool implementation

// 2018/09/19 modified by Tsung-Wei Huang

// - added binary_tree benchmark

// - added modulo_insertions benchmark

// - refactored benchmark calls

// 2018/08/31 contributed by Guannan

// Examples to test different threadpool implementations:

// - SimpleThreadpool

// - ProactiveThreadpool

// - SpeculativeThreadpool

// - PrivatizedThreadpool

#include <taskflow/threadpool/threadpool.hpp>

#include <chrono>

#include <cmath>

#include <random>

#include <numeric>

#include <climits>

#include <iomanip>

constexpr int WIDTH = 12;

using Closure = std::function<void()>;

// Procedure: benchmark

#define BENCHMARK(TITLE, F) \

std::cout \

<< std::setw(WIDTH) << TITLE << std::flush \

<< std::setw(WIDTH) << F<tf::SimpleThreadpool<Closure>>() << std::flush \

<< std::setw(WIDTH) << F<tf::ProactiveThreadpool<Closure>>() << std::flush \

<< std::setw(WIDTH) << F<tf::SpeculativeThreadpool<Closure>>() << std::flush \

<< std::setw(WIDTH) << F<tf::WorkStealingThreadpool<Closure>>() << std::flush \

<< std::endl;

// ============================================================================

// Divide and conquer to solve max subarray sum problem

// https://www.geeksforgeeks.org/divide-and-conquer-maximum-sum-subarray/

// ============================================================================

constexpr auto tree_height = 20u;

constexpr auto total_nodes = 1u << tree_height;

void update_max(std::atomic<int>& max_val, const int value) {

int old = max_val;

while(old < value && !max_val.compare_exchange_weak(old, value));

}

int max_cross_sum(const std::vector<int>& vec, int l, int m, int r){

// Include elements on left of mid.

auto sum = 0;

auto left_sum = INT_MIN;

for (auto i = m; i >= l; i--){

sum = sum + vec[i];

if (sum > left_sum)

left_sum = sum;

}

// Include elements on right of mid

sum = 0;

auto right_sum = INT_MIN;

for (auto i = m+1; i <= r; i++)

{

sum = sum + vec[i];

if (sum > right_sum)

right_sum = sum;

}

// Return sum of elements on left and right of mid

return left_sum + right_sum;

}

template<typename T>

void max_subsum(

const std::vector<int>& vec,

int l, int r,

std::atomic<int>& max_num,

T& tp,

std::atomic<size_t>& counter,

std::promise<void>& promise

) {

// Base Case: Only one element

if (l == r) {

update_max(max_num, vec[l]);

if(++counter == total_nodes*2-1){

promise.set_value();

}

return ;

}

// Find middle point

int m = (l + r)/2;

tp.emplace([&, l=l, m=m] () {

max_subsum(vec, l, m, max_num, tp, counter, promise);

});

tp.emplace([&, m=m, r=r] () {

max_subsum(vec, m+1, r, max_num, tp, counter, promise);

});

update_max(max_num, max_cross_sum(vec, l, m, r));

if(++counter == total_nodes*2-1){

promise.set_value();

}

template<typename T>

auto subsum(){

std::vector<int> vec(total_nodes);

std::iota(vec.begin(), vec.end(), -50);

std::atomic<int> result {INT_MIN};

std::atomic<size_t> counter{0};

std::promise<void> promise;

auto future = promise.get_future();

auto start = std::chrono::high_resolution_clock::now();

T tp(std::thread::hardware_concurrency());

max_subsum(vec, 0, total_nodes-1, result, tp, counter, promise);

future.get();

auto end = std::chrono::high_resolution_clock::now();

auto elapsed = std::chrono::duration_cast<std::chrono::milliseconds>(end - start);

return elapsed.count();

}

// ============================================================================

// Dynamic tasking through linear insertions

// ============================================================================

// Procedure: linear_insertions

template <typename T>

auto linear_insertions() {

const int num_threads = std::thread::hardware_concurrency();

const int num_tasks = 2000000;

auto beg = std::chrono::high_resolution_clock::now();

T threadpool(num_threads);

std::atomic<int> sum {0};

std::function<void(int)> insert;

std::promise<int> promise;

auto future = promise.get_future();

insert = [&threadpool, &insert, &sum, &promise] (int i) {

if(i > 0) {

threadpool.emplace([i=i-1, &insert] () {

insert(i);

});

}

else {

if(size_t s = ++sum; s == threadpool.num_workers()) {

promise.set_value(1);

}

};

for(int i=0; i<num_threads; i++){

insert(num_tasks / num_threads);

}

// synchronize until all tasks finish

assert(future.get() == 1);

assert(sum == num_threads);

auto end = std::chrono::high_resolution_clock::now();

return std::chrono::duration_cast<std::chrono::milliseconds>(end - beg).count();

}

// ============================================================================

// Insertions with atomic summation

// ============================================================================

// Function: atomic_add

template <typename T>

auto atomic_add() {

const int num_threads = std::thread::hardware_concurrency();

const int num_tasks = 1000000;

std::atomic<int> counter(0);

auto beg = std::chrono::high_resolution_clock::now();

std::promise<void> promise;

auto future = promise.get_future();

T threadpool(num_threads);

for(size_t i=0; i<num_tasks; i++){

threadpool.emplace([&](){

if(counter.fetch_add(1, std::memory_order_relaxed) + 1 == num_tasks) {

promise.set_value();

}

});

}

future.get();

assert(counter == num_tasks);

auto end = std::chrono::high_resolution_clock::now();

return std::chrono::duration_cast<std::chrono::milliseconds>(end - beg).count();

}

// ============================================================================

// skewed insertions

// ============================================================================

// Function: nested_insertions

template <typename T>

auto nested_insertions() {

const int num_threads = std::thread::hardware_concurrency();

const int num_tasks = 32;

auto beg = std::chrono::high_resolution_clock::now();

std::atomic<int64_t> counter(0);

std::promise<void> promise;

auto future = promise.get_future();

auto increment = [&] () {

int64_t sum = 0;

for(int i=0; i<5; ++i) {

sum = (sum + 1)*num_tasks;

}

if(++counter == sum) {

promise.set_value();

}

};

T threadpool(num_threads);

threadpool.emplace([&] () {

std::this_thread::sleep_for(std::chrono::microseconds(100));