io_service作为work pool

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。
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 <port>/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"; 
    } 

    return 0; 
}