Boost::asio can perform synchronous or asynchronous operations on I/O objects such as sockets, it is necessary to understand Boost::asio, your programs, and the process of their interaction before using Boost::asio. As an example of a bootstrap, we think about what happens when a socket performs a connection operation, and we start with a synchronous example where your program needs a Io_service object, and Io_service links your program to the OS I/O device. Boost::asio::io_service Io_service;
Your program requires an I/O object to perform I/O operations, such as a TCP socketboost::asio::ip::tcp::socket socket (io_service);
The following events occur sequentially when a synchronous connection operation is performed
1. Your program initiates the connection operation by invoking the I/O object Socket.connect (server_endpoint);
2.I/O object forwarding request to Io_service
3.io_service notifies the operating system to perform a connection operation
4. The operating system returns the results of the connection operation to the Io_service
5.io_service the error of the operation into Boost::system::error_code, a error_code may be compared with a specific value, or as a boolen (false result means that no error occurred), the result is transmitted i/ O object.
6. If the operation fails the I/O object throws an exception Boost::system::error_code, if the start operation is replaced with the following Boost::system::error_code Ec;socket.connect (Server_ Endpoint, EC); Then the result of the operation is written to the Error_code type variable EC, and no exception is returned when an asynchronous operation is executed and another different sequence of events 1. Your program initiates a connection operation by invoking an I/O object socket.async_ Connect (server_endpoint, your_completion_handler); Your_completion_handler is a function or a named function object void Your_completion_ Handler (const boost::system::error_code& EC); This function object relies on the asynchronous operation being performed, and each operation is started in the appropriate manner
The 2.I/O object passes the request to Io_service
3.io_service signaling notifies the operating system to initiate an asynchronous connection
Time passes (synchronous operation will wait here)
4. The operating system puts the results of the operation in a queue to indicate that the connection is starting to complete, for Io_service to extract the results
5. Your program gets the result of the operation by calling Io_service::run () (get some other similar io_service member function), if there is an incomplete asynchronous operation Io_service::run () will block, You must call it periodically after initiating your asynchronous operation.
6. Inside Io_service::run (), io_service the result of the operation and sends it to Your_completion_handler, which is a brief flow of Boost::asio work, if you want to understand advanced functions, such as boost :: ASIO extends to other types of asynchronous operations that you need to understand more deeply.
Boost::asio Getting Started anatomy
