boost.asio服务器使用io_service作为work pool

使用io_service作为处理工作的work pool，可以看到，就是通过io_service.post投递一个Handler到io_service的队列,Handler在这个io_service.run内部得到执行，有可能你会发现，io_services.dispatch的接口也和io_service.post一样，但不同的是它是直接调用而不是经过push到队列然后在io_services.run中执行，而在这个示例当中，显然我们需要把工作交到另一个线程去完成，这样才不会影响网络接收线程池的工作以达到高效率的接收数据，这种设计与前面的netsever其实相同，这就是典型的Half Sync/Half Async。二者的区别就是netsever自己实现了工作队列，而不是直接使用io_service，这种设计实际上在win下是使用了iocp作为工作队列。

不过我更倾向于前一种设计，因为那样做，代码一切都在自己的掌握中，而io_service则是经过许多封装代码，并且本身设计只是用于处理网络完成事件的。

无论如何使用，都能感觉到使用boost.asio实现服务器，不仅是一件非常轻松的事，而且代码很漂亮，逻辑也相当清晰，这点上很不同于ACE。

#include <stdio.h>
#include <cstdlib>
#include <iostream>
#include <boost/thread.hpp>
#include <boost/aligned_storage.hpp>
#include <boost/array.hpp>
#include <boost/bind.hpp>
#include <boost/enable_shared_from_this.hpp>
#include <boost/noncopyable.hpp>
#include <boost/shared_ptr.hpp>
#include <boost/asio.hpp>

using boost::asio::ip::tcp;

class handler_allocator
    : private boost::noncopyable
{
public:
    handler_allocator()
        : in_use_(false)
    {
    }

    void* allocate(std::size_t size)
    {
        if (!in_use_ && size < storage_.size)
        {
            in_use_ = true;
            return storage_.address();
        }
        else
        {
            return ::operator new(size);
        }
    }

    void deallocate(void* pointer)
    {
        if (pointer == storage_.address())
        {
            in_use_ = false;
        }
        else
        {
            ::operator delete(pointer);
        }
    }

private:
    // Storage space used for handler-based custom memory allocation.
    boost::aligned_storage<1024> storage_;

    // Whether the handler-based custom allocation storage has been used.
    bool in_use_;
};

template <typename Handler>
class custom_alloc_handler
{
public:
    custom_alloc_handler(handler_allocator& a, Handler h)
        : allocator_(a),
        handler_(h)
    {
    }

    template <typename Arg1>
    void operator()(Arg1 arg1)
    {
        handler_(arg1);
    }

    template <typename Arg1, typename Arg2>
    void operator()(Arg1 arg1, Arg2 arg2)
    {
        handler_(arg1, arg2);
    }

    friend void* asio_handler_allocate(std::size_t size,
        custom_alloc_handler<Handler>* this_handler)
    {
        return this_handler->allocator_.allocate(size);
    }

    friend void asio_handler_deallocate(void* pointer, std::size_t /*size*/,
        custom_alloc_handler<Handler>* this_handler)
    {
        this_handler->allocator_.deallocate(pointer);
    }

private:
    handler_allocator& allocator_;
    Handler handler_;
};

// Helper function to wrap a handler object to add custom allocation.
template <typename Handler>
inline custom_alloc_handler<Handler> make_custom_alloc_handler(
    handler_allocator& a, Handler h)
{
    return custom_alloc_handler<Handler>(a, h);
}

/// A pool of io_service objects.
class io_service_pool
    : private boost::noncopyable
{
public:
    /// Construct the io_service pool.
    explicit io_service_pool(std::size_t pool_size) : next_io_service_(0)
    {
        if (pool_size == 0)
            throw std::runtime_error("io_service_pool size is 0");

        // Give all the io_services work to do so that their run() functions will not
        // exit until they are explicitly stopped.
        for (std::size_t i = 0; i < pool_size; ++i)
        {
            io_service_ptr io_service(new boost::asio::io_service);
            work_ptr work(new boost::asio::io_service::work(*io_service));
            io_services_.push_back(io_service);
            work_.push_back(work);
        }
    }

    // Run all io_service objects in the pool.
    void run()
    {
        // Create a pool of threads to run all of the io_services.
        std::vector<boost::shared_ptr<boost::thread> > threads;
        for (std::size_t i = 0; i < io_services_.size(); ++i)
        {
            boost::shared_ptr<boost::thread> thread(new boost::thread(
                boost::bind(&boost::asio::io_service::run, io_services_[i])));
            threads.push_back(thread);
        }

        // Wait for all threads in the pool to exit.
        for (std::size_t i = 0; i < threads.size(); ++i)
            threads[i]->join();
    }

    // Stop all io_service objects in the pool.
    void stop()
    {
        // Explicitly stop all io_services.
        for (std::size_t i = 0; i < io_services_.size(); ++i)
            io_services_[i]->stop();
    }

    // Get an io_service to use.
    boost::asio::io_service& get_io_service()
    {
        // Use a round-robin scheme to choose the next io_service to use.
        boost::asio::io_service& io_service = *io_services_[next_io_service_];
        ++next_io_service_;
        if (next_io_service_ == io_services_.size())
            next_io_service_ = 0;
        return io_service;
    }

private:
    typedef boost::shared_ptr<boost::asio::io_service> io_service_ptr;
    typedef boost::shared_ptr<boost::asio::io_service::work> work_ptr;

    /// The pool of io_services.
    std::vector<io_service_ptr> io_services_;

    /// The work that keeps the io_services running.
    std::vector<work_ptr> work_;

    /// The next io_service to use for a connection.
    std::size_t next_io_service_;
};

class session
    : public boost::enable_shared_from_this<session>
{
public:
    session(boost::asio::io_service& work_service
        , boost::asio::io_service& io_service)
        : socket_(io_service)
        , io_work_service(work_service)
    {
    }

    tcp::socket& socket()
    {
        return socket_;
    }

    void start()
    {
        socket_.async_read_some(boost::asio::buffer(data_),
            make_custom_alloc_handler(allocator_,
            boost::bind(&session::handle_read,
            shared_from_this(),
            boost::asio::placeholders::error,
            boost::asio::placeholders::bytes_transferred)));
    }

    void handle_read(const boost::system::error_code& error,
        size_t bytes_transferred)
    {
        if (!error)
        {
            boost::shared_ptr<std::vector<char> > buf(new std::vector<char>);

            buf->resize(bytes_transferred);
            std::copy(data_.begin(), data_.begin() + bytes_transferred, buf->begin());
            io_work_service.post(boost::bind(&session::on_receive
                , shared_from_this(), buf, bytes_transferred));

            socket_.async_read_some(boost::asio::buffer(data_),
                make_custom_alloc_handler(allocator_,
                boost::bind(&session::handle_read,
                shared_from_this(),
                boost::asio::placeholders::error,
                boost::asio::placeholders::bytes_transferred)));
        }
    }

    void handle_write(const boost::system::error_code& error)
    {
        if (!error)
        {
        }
    }

    void on_receive(boost::shared_ptr<std::vector<char> > buffers
        , size_t bytes_transferred)
    {
        char* data_stream = &(*buffers->begin());
        // in here finish the work.
        std::cout << "receive :" << bytes_transferred << " bytes." <<
            "message :" << data_stream << std::endl;
    }

private:
    // The io_service used to finish the work.
    boost::asio::io_service& io_work_service;

    // The socket used to communicate with the client.
    tcp::socket socket_;

    // Buffer used to store data received from the client.
    boost::array<char, 1024> data_;

    // The allocator to use for handler-based custom memory allocation.
    handler_allocator allocator_;
};

typedef boost::shared_ptr<session> session_ptr;

class server
{
public:
    server(short port, std::size_t io_service_pool_size)
        : io_service_pool_(io_service_pool_size)
        , io_service_work_pool_(io_service_pool_size)
        , acceptor_(io_service_pool_.get_io_service(), tcp::endpoint(tcp::v4(), port))
    {
        session_ptr new_session(new session(io_service_work_pool_.get_io_service()
            , io_service_pool_.get_io_service()));
        acceptor_.async_accept(new_session->socket(),
            boost::bind(&server::handle_accept, this, new_session,
            boost::asio::placeholders::error));
    }

    void handle_accept(session_ptr new_session,
        const boost::system::error_code& error)
    {
        if (!error)
        {
            new_session->start();
            new_session.reset(new session(io_service_work_pool_.get_io_service()
                , io_service_pool_.get_io_service()));
            acceptor_.async_accept(new_session->socket(),
                boost::bind(&server::handle_accept, this, new_session,
                boost::asio::placeholders::error));
        }
    }

    void run()
    {
        io_thread_.reset(new boost::thread(boost::bind(&io_service_pool::run
            , &io_service_pool_)));
        work_thread_.reset(new boost::thread(boost::bind(&io_service_pool::run
            , &io_service_work_pool_)));
    }

    void stop()
    {
        io_service_pool_.stop();
        io_service_work_pool_.stop();

        io_thread_->join();
        work_thread_->join();
    }

private:
    boost::shared_ptr<boost::thread> io_thread_;
    boost::shared_ptr<boost::thread> work_thread_;
    io_service_pool io_service_pool_;
    io_service_pool io_service_work_pool_;
    tcp::acceptor acceptor_;
};

int main(int argc, char* argv[])
{
    try
    {
        if (argc != 2)
        {
            std::cerr << "Usage: server /n";
            return 1;
        }

        using namespace std; // For atoi.
        server s(atoi(argv[1]), 10);

        s.run();

        getchar();

        s.stop();
    }
    catch (std::exception& e)
    {
        std::cerr << "Exception: " << e.what() << "/n";
    }

    getchar();
    return 0;
}