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#include <boost/asio/execution.hpp>
#include <condition_variable>
#include <iostream>
#include <memory>
#include <mutex>
#include <queue>
namespace execution = boost::asio::execution;
namespace custom_props {
struct priority
{
template <typename T>
static constexpr bool is_applicable_property_v =
execution::is_executor<T>::value;
static constexpr bool is_requirable = true;
static constexpr bool is_preferable = true;
using polymorphic_query_result_type = int;
int value() const { return value_; }
int value_ = 1;
};
constexpr priority low_priority{0};
constexpr priority normal_priority{1};
constexpr priority high_priority{2};
} // namespace custom_props
class priority_scheduler
{
public:
// A class that satisfies the Executor requirements.
class executor_type
{
public:
executor_type(priority_scheduler& ctx) noexcept
: context_(ctx), priority_(custom_props::normal_priority.value())
{
}
priority_scheduler& query(execution::context_t) const noexcept
{
return context_;
}
int query(custom_props::priority) const noexcept
{
return priority_;
}
executor_type require(custom_props::priority pri) const
{
executor_type new_ex(*this);
new_ex.priority_ = pri.value();
return new_ex;
}
template <class Func>
void execute(Func f) const
{
auto p(std::make_shared<item<Func>>(priority_, std::move(f)));
std::lock_guard<std::mutex> lock(context_.mutex_);
context_.queue_.push(p);
context_.condition_.notify_one();
}
friend bool operator==(const executor_type& a,
const executor_type& b) noexcept
{
return &a.context_ == &b.context_;
}
friend bool operator!=(const executor_type& a,
const executor_type& b) noexcept
{
return &a.context_ != &b.context_;
}
private:
priority_scheduler& context_;
int priority_;
};
executor_type executor() noexcept
{
return executor_type(*const_cast<priority_scheduler*>(this));
}
void run()
{
std::unique_lock<std::mutex> lock(mutex_);
for (;;)
{
condition_.wait(lock, [&]{ return stopped_ || !queue_.empty(); });
if (stopped_)
return;
auto p(queue_.top());
queue_.pop();
lock.unlock();
p->execute_(p);
lock.lock();
}
}
void stop()
{
std::lock_guard<std::mutex> lock(mutex_);
stopped_ = true;
condition_.notify_all();
}
private:
struct item_base
{
int priority_;
void (*execute_)(std::shared_ptr<item_base>&);
};
template <class Func>
struct item : item_base
{
item(int pri, Func f) : function_(std::move(f))
{
priority_ = pri;
execute_ = [](std::shared_ptr<item_base>& p)
{
Func tmp(std::move(static_cast<item*>(p.get())->function_));
p.reset();
tmp();
};
}
Func function_;
};
struct item_comp
{
bool operator()(
const std::shared_ptr<item_base>& a,
const std::shared_ptr<item_base>& b)
{
return a->priority_ < b->priority_;
}
};
std::mutex mutex_;
std::condition_variable condition_;
std::priority_queue<
std::shared_ptr<item_base>,
std::vector<std::shared_ptr<item_base>>,
item_comp> queue_;
bool stopped_ = false;
};
int main()
{
priority_scheduler sched;
auto ex = sched.executor();
auto prefer_low = boost::asio::prefer(ex, custom_props::low_priority);
auto low = boost::asio::require(ex, custom_props::low_priority);
auto med = boost::asio::require(ex, custom_props::normal_priority);
auto high = boost::asio::require(ex, custom_props::high_priority);
execution::any_executor<custom_props::priority> poly_high(high);
execution::execute(prefer_low, []{ std::cout << "1\n"; });
execution::execute(low, []{ std::cout << "11\n"; });
execution::execute(low, []{ std::cout << "111\n"; });
execution::execute(med, []{ std::cout << "2\n"; });
execution::execute(med, []{ std::cout << "22\n"; });
execution::execute(high, []{ std::cout << "3\n"; });
execution::execute(high, []{ std::cout << "33\n"; });
execution::execute(high, []{ std::cout << "333\n"; });
execution::execute(poly_high, []{ std::cout << "3333\n"; });
execution::execute(boost::asio::require(ex, custom_props::priority{-1}), [&]{ sched.stop(); });
sched.run();
std::cout << "polymorphic query result = " << boost::asio::query(poly_high, custom_props::priority{}) << "\n";
}
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