cpp-taskflow/examples/parallel_reduce.cpp at master · feiyunwill/cpp-taskflow · GitHub

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// This example demonstrates how to create a parallel-reduction task.

#include <taskflow/taskflow.hpp>

#include <taskflow/algorithm/reduce.hpp>

struct Data {

int a {::rand()};

int b {::rand()};

int transform() const {

return a*a + 2*a*b + b*b;

}

};

// Procedure: reduce

// This procedure demonstrates

void reduce(size_t N) {

std::cout << "Benchmark: reduce" << std::endl;

std::vector<int> data;

data.reserve(N);

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

data.push_back(::rand());

}

// sequential method

auto sbeg = std::chrono::steady_clock::now();

auto smin = std::numeric_limits<int>::max();

for(auto& d : data) {

smin = std::min(smin, d);

}

auto send = std::chrono::steady_clock::now();

std::cout << "[sequential] reduce: "

<< std::chrono::duration_cast<std::chrono::microseconds>(send - sbeg).count()

<< " us\n";

// taskflow

auto tbeg = std::chrono::steady_clock::now();

tf::Taskflow taskflow;

tf::Executor executor;

auto tmin = std::numeric_limits<int>::max();

taskflow.reduce(

data.begin(),

data.end(),

tmin,

[] (int& l, const auto& r) { return std::min(l, r); }

);

executor.run(taskflow).get();

auto tend = std::chrono::steady_clock::now();

std::cout << "[taskflow] reduce: "

<< std::chrono::duration_cast<std::chrono::microseconds>(tend - tbeg).count()

<< " us\n";

// assertion

if(tmin == smin) {

std::cout << "result is correct" << std::endl;

}

else {

std::cout << "result is incorrect: " << smin << " != " << tmin << std::endl;

}

taskflow.dump(std::cout);

}

// Procedure: transform_reduce

void transform_reduce(size_t N) {

std::cout << "Benchmark: transform_reduce" << std::endl;

std::vector<Data> data(N);

// sequential method

auto sbeg = std::chrono::steady_clock::now();

auto smin = std::numeric_limits<int>::max();

for(auto& d : data) {

smin = std::min(smin, d.transform());

}

auto send = std::chrono::steady_clock::now();

std::cout << "[sequential] transform_reduce "

<< std::chrono::duration_cast<std::chrono::microseconds>(send - sbeg).count()

<< " us\n";

// taskflow

auto tbeg = std::chrono::steady_clock::now();

tf::Taskflow tf;

auto tmin = std::numeric_limits<int>::max();

tf.transform_reduce(data.begin(), data.end(), tmin,

[] (int l, int r) { return std::min(l, r); },

[] (const Data& d) { return d.transform(); }

);

tf::Executor().run(tf).get();

auto tend = std::chrono::steady_clock::now();

std::cout << "[taskflow] transform_reduce "

<< std::chrono::duration_cast<std::chrono::microseconds>(tend - tbeg).count()

<< " us\n";

// assertion

assert(tmin == smin);

}

void reduce_by_index(size_t N) {

std::cout << "Benchmark: reduce_by_key" << std::endl;

tf::Executor executor;

tf::Taskflow taskflow;

std::vector<double> data(N);

double res = 1.0;

auto tbeg = std::chrono::steady_clock::now();

taskflow.reduce_by_index(

tf::IndexRange<size_t>(0, N, 1),

// final result

res,

// local reducer

[&](tf::IndexRange<size_t> subrange, std::optional<double> running_total) {

double residual = running_total ? *running_total : 0.0;

for(size_t i=subrange.begin(); i<subrange.end(); i+=subrange.step_size()) {

data[i] = 1.0;

residual += data[i];

}

printf("partial sum = %lf\n", residual);

return residual;

// global reducer

std::plus<double>()

);

executor.run(taskflow).wait();

auto tend = std::chrono::steady_clock::now();

std::cout << "[taskflow] reduce_by_key "

<< std::chrono::duration_cast<std::chrono::microseconds>(tend - tbeg).count()

<< " us\n";

}

// ----------------------------------------------------------------------------

// Function: main

int main(int argc, char* argv[]) {

if(argc != 3) {

std::cerr << "usage: ./reduce [reduce|transform_reduce|reduce_by_index] N" << std::endl;

std::exit(EXIT_FAILURE);

}

if(std::strcmp(argv[1], "reduce") == 0) {

reduce(std::stoul(argv[2]));

}

else if(std::strcmp(argv[1], "transform_reduce") == 0) {

transform_reduce(std::stoul(argv[2]));

}

else if(std::strcmp(argv[1], "reduce_by_index") == 0) {

reduce_by_index(std::stoul(argv[2]));

}

else {

std::cerr << "invalid method " << argv[1] << std::endl;

std::exit(EXIT_FAILURE);

}

return 0;

}

cpp-taskflow/examples/parallel_reduce.cpp at master · feiyunwill/cpp-taskflow · GitHub

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