boost库asio详解3——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;
 }