Geek Answers Handbook

How to use boost :: packaged_task, function parameters and boost :: asio :: io_service?

First of all, I want to apologize for the long post. I wanted to be as thorough as possible.

I have been stuck with this problem for several days, and there is surprisingly little information about the proper use boost::packaged_taskfor a function that has input parameters.

System Information

  • C ++ 03
  • Boost 1.54.0
  • CMake 2.8.9

Initial requirement

  • I have a setup consisting of clients, server and devices.
  • The client interacts with the device by sending requests to the server.
    • These requests are checked and sent to the appropriate device.
    • Requests are processed asynchronously, and they are sometimes queued through boost::asio::io_service::strandfor various reasons.
  • , .
    • ( ), .

boost:: futures , boost:: packaged_task , . , , .

, packaged_task :

  • packaged_task<R>
  • packaged_task<R()>
  • packaged_task<R(ArgTypes)>
  • , .

, ; boost:: futures . :

  • int return, .
  • int return, .
  • std::string return, .
  • std::string return, .

std::string ans("forty two");

int int_no_params()
{
    return 42;
}

int int_with_params(int param)
{
    return param;
}

std::string string_no_params()
{
    return std::string("forty two");
}

std::string string_with_params(std::string & param) // Have tried both with and without '&'
{
    return param;
}

1:

int function(void)

    //! Compiles and produces correct result.  
    {
        boost::packaged_task<int()> example(int_no_params);
        boost::future<int> f = example.get_future();
        boost::thread task(boost::move(example));
        int answer = f.get();
        std::cout << "Answer to life and whatnot, in English: " << answer << std::endl;
        task.join();
    }

2:

std::string function(void)

    //! Compiles and produces correct result.
    {
        boost::packaged_task<std::string()> example(string_no_params);
        boost::future<std::string> f = example.get_future();
        boost::thread task(boost::move(example));
        std::string answer = f.get();
        std::cout << "string_no_params: " << answer << std::endl;
        task.join();
    }

3:

std::string(std::string& param)

//! Doesn't compile.
//! error: variable ‘boost::packaged_task<std::basic_string<char>(std::basic_string<char>&)> example’ has initializer but incomplete type

{
    boost::packaged_task<std::string(std::string&)> example(string_with_params);
    boost::future<std::string> f = example.get_future();
    example(ans);
    std::string answer = f.get();
    std::cout << "string_with_params: " << answer << std::endl;
}

4:

boost:: threading

//! Doesn't compile.
//! error: variable ‘boost::packaged_task<std::basic_string<char>(std::basic_string<char>&)> example’ has initializer but incomplete type
{
    boost::packaged_task<std::string(std::string&)> example(string_with_params);
    boost::future<std::string> f = example.get_future();
    boost::thread task(boost::move(example), ans);
    std::string answer = f.get();
    std::cout << "string_with_params: " << answer << std::endl;
    task.join();
}

5:

packaged_task

//! Doesn't compile in C++03, C++11 only.
//! error: extended initializer lists only available with -std=c++11 or -std=gnu++11 [-Werror]
{
    boost::packaged_task<std::string(std::string&)> example
    { boost::bind(&string_with_params, ans) };
    boost::future<std::string> f = example.get_future();
    boost::thread task(boost::move(example), ans);
    std::string answer = f.get();
    std::cout << "string_with_params: " << answer << std::endl;
    task.join();
}

6:

, shared_ptr

typedef boost::packaged_task<std::string(std::string&)> task_t;

, shared_ptr<T>::operator() task .

// error: invalid use of incomplete type ‘class boost::packaged_task<std::basic_string<char>(std::basic_string<char>&)>’
// error: incomplete type ‘task_t {aka boost::packaged_task<std::basic_string<char>(std::basic_string<char>&)>}’ used in nested name specifier
// boost/thread/future.hpp:1320:11: error: declaration of ‘class boost::packaged_task<std::basic_string<char>(std::basic_string<char>&)>’
{
    boost::shared_ptr<task_t> example = boost::make_shared<task_t>(boost::bind(&string_with_params, ans));
    boost::future<std::string> f = example->get_future();
    boost::thread task(boost::bind(&task_t::operator(), example));
    std::string answer = f.get();
    std::cout << "string_with_params: " << answer << std::endl;
    task.join();
}

7:

boost::asio::io_service boost::bind

//: . class boost:: packaged_task (std:: basic_string &) >   //error: incomplete type 'task_t {aka boost:: packaged_task (std:: basic_string &) > }       //boost/thread/future.hpp: 1320: 11: : boost:: packaged_task (std:: basic_string &) >

{
    boost::asio::io_service io_service;
    boost::thread_group threads;
    boost::asio::io_service::work work(io_service);

    for (int i = 0; i < 3; ++i)
    {
        threads.create_thread(boost::bind(&boost::asio::io_service::run,
            &io_service));
    }

    boost::shared_ptr<task_t> example = boost::make_shared<task_t>(boost::bind(&string_with_params, ans));
    boost::future<std::string> f = example->get_future();
    io_service.post(boost::bind(&task_t::operator(), example));
    std::string answer = f.get();
    std::cout << "string_with_params: " << answer << std::endl;
    threads.join_all();
}

-, ? , . , , , . , .

:

promises, . , , -, .

.

+4
1

, , , Boost.Thread packaged_task ++ 11:

++ 11: ArgTypes packaged_task. BOOST_THREAD_PROVIDES_SIGNATURE_PACKAGED_TASK ( Boost 1.55).

ticket , , , ​​ R().

++ 03 , 3-7 . , 6 7. task_t std::string(std::string&), boost::bind(). , , packaged_task, std::string().

packaged_task ++ 03, , boost::promise. operator(). , -, promise future:

/// @brief basic_task to support function types with arguments.  This
///        provides a minimal feature workaround to Boost.Thread's
///        packaged_task not supporting argument types for C++03.
template <typename Fn>
class basic_task
{
public:
  // @brief The type the future will return.
  typedef typename boost::function_types::result_type<Fn>::type result_type;

  typedef boost::promise<result_type> promise_type;

  /// @brief Constructor.
  template <typename F> 
  explicit basic_task(const F& f)
    : fn_(f),
      promise_(boost::make_shared<promise_type>())
  {}

  // Overload operator() functions.

  void operator()()
  {
    promise_->set_value(fn_());
  }

  template <typename A1>
  void operator()(const A1& a1)
  {
    promise_->set_value(fn_(a1));
  }

  template <typename A1>
  void operator()(A1& a1)
  {
    promise_->set_value(fn_(a1));
  }

  /// @brief Get a future for this task' promise.
  boost::unique_future<result_type>
  get_future()
  {
    return promise_->get_future();
  }

private:
  boost::function<Fn> fn_;
  boost::shared_ptr<promise_type> promise_;
};

:

#include <iostream>
#include <string>

#define BOOST_THREAD_PROVIDES_SIGNATURE_PACKAGED_TASK

#include <boost/asio.hpp>
#include <boost/function_types/result_type.hpp>
#include <boost/make_shared.hpp>
#include <boost/thread.hpp>

/// @brief basic_task to support function types with arguments.  This
///        provides a minimal feature workaround to Boost.Thread's
///        packaged_task not supporting argument types for C++03.
template <typename Fn>
class basic_task
{
public:
  // @brief The type the future will return.
  typedef typename boost::function_types::result_type<Fn>::type result_type;

  typedef boost::promise<result_type> promise_type;

  /// @brief Constructor.
  template <typename F> 
  explicit basic_task(const F& f)
    : fn_(f),
      promise_(boost::make_shared<promise_type>())
  {}

  // Overload operator() functions.

  void operator()()
  {
    promise_->set_value(fn_());
  }

  template <typename A1>
  void operator()(const A1& a1)
  {
    promise_->set_value(fn_(a1));
  }

  template <typename A1>
  void operator()(A1& a1)
  {
    promise_->set_value(fn_(a1));
  }

  /// @brief Get a future for this task' promise.
  boost::unique_future<result_type>
  get_future()
  {
    return promise_->get_future();
  }

private:
  boost::function<Fn> fn_;
  boost::shared_ptr<promise_type> promise_;
};

std::string ans("forty two");

int int_no_params()
{
  return 42;
}

int int_with_params(int param)
{
  return param;
}

std::string string_no_params()
{
  return std::string("forty two");
}

std::string string_with_params(std::string & param)
{
  return param;
}

int main()
{
  // example 1
  {
    boost::packaged_task<int()> example(&int_no_params);
    boost::unique_future<int> f = example.get_future();
    boost::thread task(boost::move(example));
    int answer = f.get();
    std::cout << "Answer to life and whatnot, in English: "
              << answer << std::endl;
    task.join();
  }

  // example 2
  {
    boost::packaged_task<std::string()> example(&string_no_params);
    boost::unique_future<std::string> f = example.get_future();
    boost::thread task(boost::move(example));
    std::string answer = f.get();
    std::cout << "string_no_params: " << answer << std::endl;
    task.join();
  }

  // example 3
  {
    basic_task<std::string(std::string&)> example(&string_with_params);
    boost::unique_future<std::string> f = example.get_future();
    example(ans);
    std::string answer = f.get();
    std::cout << "string_with_params: " << answer << std::endl;
  }

  // example 4
  {
    basic_task<std::string(std::string&)> example(&string_with_params);
    boost::unique_future<std::string> f = example.get_future();
    boost::thread task(boost::move(example), ans);
    std::string answer = f.get();
    std::cout << "string_with_params: " << answer << std::endl;
    task.join();
  }

  // example 5
  {
    basic_task<std::string(std::string&)>
        example(boost::bind(&string_with_params, ans));
    boost::unique_future<std::string> f = example.get_future();
    boost::thread task(boost::move(example), ans);
    std::string answer = f.get();
    std::cout << "string_with_params: " << answer << std::endl;
    task.join();
  }

  // example 6
  {
    typedef boost::packaged_task<std::string()> task_t;
    boost::shared_ptr<task_t> example =
        boost::make_shared<task_t>(boost::bind(&string_with_params, ans));
    boost::unique_future<std::string> f = example->get_future();
    boost::thread task(boost::bind(&task_t::operator(), example));
    std::string answer = f.get();
    std::cout << "string_with_params: " << answer << std::endl;
    task.join();
  }

  // example 7
  {
    boost::asio::io_service io_service;
    boost::thread_group threads;
    boost::asio::io_service::work work(io_service);

    for (int i = 0; i < 3; ++i)
      threads.create_thread(
          boost::bind(&boost::asio::io_service::run, &io_service));

    typedef boost::packaged_task<std::string()> task_t;
    boost::shared_ptr<task_t> example =
        boost::make_shared<task_t>(boost::bind(&string_with_params, ans));
    boost::unique_future<std::string> f = example->get_future();
    io_service.post(boost::bind(&task_t::operator(), example));
    std::string answer = f.get();
    std::cout << "string_with_params: " << answer << std::endl;
    io_service.stop();
    threads.join_all();
  }
}

:

Answer to life and whatnot, in English: 42
string_no_params: forty two
string_with_params: forty two
string_with_params: forty two
string_with_params: forty two
string_with_params: forty two
string_with_params: forty two
+5

More articles:


All Articles