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#include <chrono>
#include <vector>
#include <iostream>
#include <algorithm>
#include <string>
#include <thread>
#include <random>
#include <cstddef>
#include <algorithm>
#include <concepts>
#include <future>
#include <ranges>
class Measure
{
public:
Measure()
: start(std::chrono::high_resolution_clock::now())
{
}
~Measure()
{
auto end = std::chrono::high_resolution_clock::now();
std::chrono::duration<double> delta = end - start;
std::cout << " " << delta.count() * 1000 << " ms passed" << std::endl;
}
std::chrono::time_point<std::chrono::high_resolution_clock> start{};
};
template<typename Callable>
void measure(const std::string& text, Callable c)
{
std::cout << text << ":\n";
for(int i = 0; i < 3; ++i)
{ // RAII timed scoped
Measure m;
c();
}
}
template<typename T>
std::vector<T> get_random_vector(std::size_t size,
T min = std::numeric_limits<T>::min(),
T max = std::numeric_limits<T>::max())
{
std::default_random_engine generator;
// Randomly generate T-values from the range [min; max]
std::uniform_int_distribution<T> distrib(min, max);
std::vector<T> v;
v.resize(size);
for(auto& item : v)
{
item = distrib(generator);
}
return v;
}
std::vector<std::string> get_random_strings(std::size_t size,
std::size_t length,
char min, char max)
{
std::default_random_engine generator;
// Randomly generate T-values from the range [min; max]
std::uniform_int_distribution<char> distrib(min, max);
std::vector<std::string> v;
v.resize(size);
for(auto& str : v)
{
str.reserve(length);
for(auto i = 0u; i < str.capacity(); ++i)
{
str += distrib(generator);
}
}
return v;
}
template<typename C, typename T>
// requires std::forward_iterator<Iter>
requires std:: ranges::input_range<C>
//std::vector<const T*> find_all(Iter begin, Iter end, const T& key)
std::vector<const T*> find_all(const C& c, const T& key)
{
std::vector<const T*> res{};
std::for_each(c.begin(), c.end(),
[&key, &res](const T& value)
{
if(value == key)
{
res.push_back(&value);
}
});
return res;
}
template<typename C, typename T>
//requires /*std::is_container<C> &&*/ std::is_same<C::value_type, T>::value
requires std:: ranges::input_range<C>
std::vector<const T*> find_all(const C& v, const T& key, std::size_t n)
{
std::condition_variable cv;
bool run{false};
std::vector<const T*> res{};
// Calculate the chunk size needed for splitting the values into
// (at most) n portions and at least 1 big portion.
std::ptrdiff_t chunk_size =
static_cast<std::ptrdiff_t>(std::ceil(static_cast<float>(v.size()) / static_cast<float>(n)));
std::vector<std::future<std::vector<const T*>>> futures;
auto begin = v.begin();
auto end = v.end();
while(begin < v.end())
{
end = begin + chunk_size;
if(end > v.end())
{
end = v.end();
}
// create suspended thread for searching on [begin, end[ range
futures.emplace_back(std::async(std::launch::async,
[&key, &cv, &run, begin, end]()
{
std::mutex m;
std::unique_lock lk(m);
cv.wait(lk, [&run](){ return run; });
return find_all(std::ranges::subrange(begin, end), key);
}));
begin = end;
}
{
Measure meas;
// Signal all threads to run
run = true;
cv.notify_all();
// Get and append the result from each thread into accumulated results
// vector
for(auto& future : futures)
{
auto v = future.get();
res.insert(res.end(), v.begin(), v.end());
}
}
return res;
}
int main()
{
{
auto v = get_random_vector<int>(10'000'000, 0, 100);
// std::array<int, 10> v{1,2,42,4,5,6,7,8,42,10}; // - this also works
// int v[] = {1,2,42,4,5,6,7,8,42,10}; // - doesn't seem to work :-(
// 42 is expected to be in the vector in ~1/100th of the indices
int needle{42};
std::size_t found_items{};
{ // non-threaded
measure("Single threaded search for int",
[&]()
{
auto res = find_all(v, needle);
found_items = res.size(); // consider this the 'truth"
});
}
for(auto num_threads = 1u; num_threads < 17u; ++num_threads)
{
std::cout << "Multi threaded (" << num_threads << ") search for int:\n";
for(int i = 0; i < 3; ++i)
{
auto res = find_all(v, needle, num_threads);
if(res.size() != found_items)
{
std::cout << "That was unexpected!\n";
}
}
}
}
{
auto v = get_random_strings(10'000'000, 20, 'a', 'z');
// Pick middle string as needle so we get one match:
std::string needle{v[v.size() / 2]};
{ // non-threaded
measure("Single threaded search for string",
[&]()
{
auto res = find_all(v, needle);
if(res.size() != 1)
{
std::cout << "That was unexpected!\n";
}
});
}
for(auto num_threads = 1u; num_threads < 17u; ++num_threads)
{
std::cout << "Multi threaded (" << num_threads << ") search for string:\n";
for(int i = 0; i < 3; ++i)
{
auto res = find_all(v, needle, num_threads);
if(res.size() != 1)
{
std::cout << "That was unexpected!\n";
}
}
}
}
}
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