boost asio 学习(六) 定时器

http://www.gamedev.net/blog/950/entry-2249317-a-guide-to-getting-
started-with-boostasio?pg=7

6 定时器

boost::asio 提供了一个 deadline_timer class来提供同步与异步的接口。
BOOST文档提供了一组优秀示例。
第一个例子，将创建一个间隔5秒的定时器。

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#include <boost/asio.hpp> #include <boost/shared_ptr.hpp> #include <boost/thread.hpp> #include <boost/thread/mutex.hpp> #include <boost/bind.hpp> #include <iostream>   boost::mutex global_stream_lock;   void WorkerThread(boost::shared_ptr< boost::asio::io_service >   io_service) {     global_stream_lock.lock();     std::cout << "[" << boost::this_thread::get_id()         << "] Thread Start" << std::endl;     global_stream_lock.unlock();       while (true)     {         try         {             boost::system::error_code ec;             io_service->run(ec);             if (ec)             {                 global_stream_lock.lock();                 std::cout << "[" <<   boost::this_thread::get_id()                     << "] Error: " << ec <<   std::endl;                 global_stream_lock.unlock();             }             break;         }         catch (std::exception & ex)         {             global_stream_lock.lock();             std::cout << "[" <<   boost::this_thread::get_id()                 << "] Exception: " << ex.what() <<   std::endl;             global_stream_lock.unlock();         }     }       global_stream_lock.lock();     std::cout << "[" << boost::this_thread::get_id()         << "] Thread Finish" << std::endl;     global_stream_lock.unlock(); }   void TimerHandler(const boost::system::error_code & error) {     if (error)     {         global_stream_lock.lock();         std::cout << "[" << boost::this_thread::get_id()             << "] Error: " << error << std::endl;         global_stream_lock.unlock();     }     else     {         global_stream_lock.lock();         std::cout << "[" << boost::this_thread::get_id()             << "] TimerHandler " << std::endl;         global_stream_lock.unlock();     } }   int main(int argc, char * argv[]) {     boost::shared_ptr< boost::asio::io_service > io_service(         new boost::asio::io_service         );     boost::shared_ptr< boost::asio::io_service::work > work(         new boost::asio::io_service::work(*io_service)         );       global_stream_lock.lock();     std::cout << "[" << boost::this_thread::get_id()         << "] Press [return] to exit." << std::endl;     global_stream_lock.unlock();       boost::thread_group worker_threads;     for (int x = 0; x < 2; ++x)     {         worker_threads.create_thread(boost::bind   (&WorkerThread, io_service));     }       boost::asio::deadline_timer timer(*io_service);     timer.expires_from_now(boost::posix_time::seconds(5));     timer.async_wait(TimerHandler);       std::cin.get();       io_service->stop();       worker_threads.join_all();       return 0; }

　　

如果我们想创建一个可冲用的定时器.我们将定时器对象设置为全局，但是可能
导致共享对象不是线程安全的。boost::bind能解决这个问题。使用定时器对象
的shared_ptr指针，我们能使用bind并且传递定时器到指定的handler，保持定
时器可重用。

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#include <boost/asio.hpp> #include <boost/shared_ptr.hpp> #include <boost/thread.hpp> #include <boost/thread/mutex.hpp> #include <boost/bind.hpp> #include <iostream>   boost::mutex global_stream_lock;   void WorkerThread(boost::shared_ptr< boost::asio::io_service >   io_service) {     global_stream_lock.lock();     std::cout << "[" << boost::this_thread::get_id()         << "] Thread Start" << std::endl;     global_stream_lock.unlock();       while (true)     {         try         {             boost::system::error_code ec;             io_service->run(ec);             if (ec)             {                 global_stream_lock.lock();                 std::cout << "[" <<   boost::this_thread::get_id()                     << "] Error: " << ec <<   std::endl;                 global_stream_lock.unlock();             }             break;         }         catch (std::exception & ex)         {             global_stream_lock.lock();             std::cout << "[" <<   boost::this_thread::get_id()                 << "] Exception: " << ex.what() <<   std::endl;             global_stream_lock.unlock();         }     }       global_stream_lock.lock();     std::cout << "[" << boost::this_thread::get_id()         << "] Thread Finish" << std::endl;     global_stream_lock.unlock(); }   void TimerHandler(     const boost::system::error_code & error,     boost::shared_ptr< boost::asio::deadline_timer > timer     ) {     if (error)     {         global_stream_lock.lock();         std::cout << "[" << boost::this_thread::get_id()             << "] Error: " << error << std::endl;         global_stream_lock.unlock();     }     else     {         global_stream_lock.lock();         std::cout << "[" << boost::this_thread::get_id()             << "] TimerHandler " << std::endl;         global_stream_lock.unlock();           timer->expires_from_now(boost::posix_time::seconds   (5));         timer->async_wait(boost::bind(&TimerHandler, _1,   timer));     } }   int main(int argc, char * argv[]) {     boost::shared_ptr< boost::asio::io_service > io_service(         new boost::asio::io_service         );     boost::shared_ptr< boost::asio::io_service::work > work(         new boost::asio::io_service::work(*io_service)         );       global_stream_lock.lock();     std::cout << "[" << boost::this_thread::get_id()         << "] Press [return] to exit." << std::endl;     global_stream_lock.unlock();       boost::thread_group worker_threads;     for (int x = 0; x < 2; ++x)     {         worker_threads.create_thread(boost::bind   (&WorkerThread, io_service));     }       boost::shared_ptr< boost::asio::deadline_timer > timer(         new boost::asio::deadline_timer(*io_service)         );     timer->expires_from_now(boost::posix_time::seconds(5));     timer->async_wait(boost::bind(&TimerHandler, _1, timer));       std::cin.get();       io_service->stop();       worker_threads.join_all();       return 0; }

　　

使用bind可以做许多有趣的事情，_1参数是一个占位符。因为TimerHandler 函
数需要一个参数用于回调，我们需要引用这个bind调用。_1意味着第一个参数，
我们稍后提供。

运行上面例子，我们将获得一个每五秒激活一次的定时器。
如果想保证定时器不和work处理器同时运行，我们可以使用strand。
代码如下

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#include <boost/asio.hpp> #include <boost/shared_ptr.hpp> #include <boost/thread.hpp> #include <boost/thread/mutex.hpp> #include <boost/bind.hpp> #include <iostream>   boost::mutex global_stream_lock;   void WorkerThread(boost::shared_ptr< boost::asio::io_service > io_service) {     global_stream_lock.lock();     std::cout << "[" << boost::this_thread::get_id()         << "] Thread Start" << std::endl;     global_stream_lock.unlock();       while (true)     {         try         {             boost::system::error_code ec;             io_service->run(ec);             if (ec)             {                 global_stream_lock.lock();                 std::cout << "[" << boost::this_thread::get_id()                     << "] Error: " << ec << std::endl;                 global_stream_lock.unlock();             }             break;         }         catch (std::exception & ex)         {             global_stream_lock.lock();             std::cout << "[" << boost::this_thread::get_id()                 << "] Exception: " << ex.what() << std::endl;             global_stream_lock.unlock();         }     }       global_stream_lock.lock();     std::cout << "[" << boost::this_thread::get_id()         << "] Thread Finish" << std::endl;     global_stream_lock.unlock(); }   void TimerHandler(     const boost::system::error_code & error,     boost::shared_ptr< boost::asio::deadline_timer > timer,     boost::shared_ptr< boost::asio::io_service::strand > strand     ) {     if (error)     {         global_stream_lock.lock();         std::cout << "[" << boost::this_thread::get_id()             << "] Error: " << error << std::endl;         global_stream_lock.unlock();     }     else     {         std::cout << "[" << boost::this_thread::get_id()             << "] TimerHandler " << std::endl;           timer->expires_from_now(boost::posix_time::seconds(1));         timer->async_wait(             strand->wrap(boost::bind(&TimerHandler, _1, timer, strand))             );     } }   void PrintNum(int x) {     std::cout << "[" << boost::this_thread::get_id()         << "] x: " << x << std::endl;     boost::this_thread::sleep(boost::posix_time::milliseconds(1000)); }   int main(int argc, char * argv[]) {     boost::shared_ptr< boost::asio::io_service > io_service(         new boost::asio::io_service         );     boost::shared_ptr< boost::asio::io_service::work > work(         new boost::asio::io_service::work(*io_service)         );     boost::shared_ptr< boost::asio::io_service::strand > strand(         new boost::asio::io_service::strand(*io_service)         );       global_stream_lock.lock();     std::cout << "[" << boost::this_thread::get_id()         << "] Press [return] to exit." << std::endl;     global_stream_lock.unlock();       boost::thread_group worker_threads;     for (int x = 0; x < 2; ++x)     {         worker_threads.create_thread(boost::bind(&WorkerThread, io_service));     }       boost::this_thread::sleep(boost::posix_time::seconds(1));       strand->post(boost::bind(&PrintNum, 1));     strand->post(boost::bind(&PrintNum, 2));     strand->post(boost::bind(&PrintNum, 3));     strand->post(boost::bind(&PrintNum, 4));     strand->post(boost::bind(&PrintNum, 5));       boost::shared_ptr< boost::asio::deadline_timer > timer(         new boost::asio::deadline_timer(*io_service)         );     timer->expires_from_now(boost::posix_time::seconds(1));     timer->async_wait(         strand->wrap(boost::bind(&TimerHandler, _1, timer, strand))         );       std::cin.get();       io_service->stop();       worker_threads.join_all();       return 0; }

　　

我们需要使用strand封装定时器处理器，strand能确保工作对象先运行而后定时器线程后运行。

本章节我们学习如何使用bind strand shard_ptr来获取灵活性和实现功能。在后面的网络系统中我们将使用这些组件。