提升ASIO异常传播

Question

我注意到，在许多Boost ASIO示例中，正在对可能抛出错误的函数进行调用，但未使用try/catch。例如，封锁UDP客户端的例子here具有以下功能：

void check_deadline() 
    { 
    // Check whether the deadline has passed. We compare the deadline against 
    // the current time since a new asynchronous operation may have moved the 
    // deadline before this actor had a chance to run. 
    if (deadline_.expires_at() <= deadline_timer::traits_type::now()) 
    { 
     // The deadline has passed. The outstanding asynchronous operation needs 
     // to be cancelled so that the blocked receive() function will return. 
     // 
     // Please note that cancel() has portability issues on some versions of 
     // Microsoft Windows, and it may be necessary to use close() instead. 
     // Consult the documentation for cancel() for further information. 
     socket_.cancel(); 

     // There is no longer an active deadline. The expiry is set to positive 
     // infinity so that the actor takes no action until a new deadline is set. 
     deadline_.expires_at(boost::posix_time::pos_infin); 
    } 

    // Put the actor back to sleep. 
    deadline_.async_wait(boost::bind(&client::check_deadline, this)); 
    } 

为deadline_.expires_at（here）的机制的文档指出，这个函数抛出一个boost ::系统:: SYSTEM_ERROR例外。

这是不是在这个例子中被捕获，因为它只是一个例子，或者像这样的调用抛出的异常通过调用run，run-one等来传播？换句话说，用try catch来调用io_service.run（）是否足以处理这些类型的异常？

此外，我还注意到deadline_.async_wait文档here指出处理程序需要一个引用boost :: system :: system_error :: error_code的签名。我在check_deadline（）函数中看不到引用或占位符。

Answer 1

basic_deadline_timer::async_wait文档状态：

Regardless of whether the asynchronous operation completes immediately or not, the handler will not be invoked from within this function. Invocation of the handler will be performed in a manner equivalent to using boost::asio::io_service::post().

这意味着该处理器将会从内部io_service::run()调用（调用它的线程），所以异常会被自动传播到用户代码，并没有特殊的处理是需要在Asio内部。通常，为了简化，样本不包含错误处理。

对不起，我不知道为什么样本中没有指定error_code占位符。需要看看Asio的消息来源。