CppCon 2016: Michael Caisse “Asynchronous IO with Boost.Asio"

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Uploaded on 10/05/2016

http://CppCon.org

Presentation Slides, PDFs, Source Code and other presenter materials are available at: https://github.com/cppcon/cppcon2016

Reactive systems are found everywhere. The temptation to implement them with legions of waiting threads can be strong; however, the result is nearly always disappointing. The Boost.Asio library provides a framework to handle asynchronous resources with specific classes directed toward networking, serial port I/O, timers and more. In this session we will introduce Asio and some best practices while implementing a simple TCP client and server.

Asio has been submitted to the C++ Standards Committee for inclusion and can be found in the Boost library collection or as a stand-alone version. Come and learn a better way to implement reactive systems with the Asynchronous I/O library.

Michael Caisse
Ciere, Inc.
Michael Caisse has been crafting code in C++ for 25-years. He is a regular speaker at various conferences and is passionate about teaching and training. Michael is the owner of Ciere Consulting which provides software consulting and contracting services, C++ training, and Project Recovery for failing multidisciplinary engineering projects. When he isn't fighting with compilers or robots, he enjoys fencing with a sabre. :: ciere.com

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Comments (6):

By anonymous    2017-09-20

Connection lifetime is a fundamental issue with boost::asio. Speaking from experience, I can assure you that getting it wrong causes "undefined behaviour"...

The asio examples use shared_ptr to ensure that a connection is kept alive whilst it may have outstanding handlers in an asio::io_service. Note that even in a single thread, an asio::io_service runs asynchronously to the application code, see CppCon 2016: Michael Caisse "Asynchronous IO with Boost.Asio" for an excellent description of the precise mechanism.

A shared_ptr enables the lifetime of a connection to be controlled by the shared_ptr instance count. IMHO it's not "cheating and cheating big"; but an elegant solution to complicated problem.

However, I agree with you that just using shared_ptr's to control connection lifetimes is not a complete solution since it can lead to resource leaks.

In my answer here: Boost async_* functions and shared_ptr's, I proposed using a combination of shared_ptr and weak_ptr to manage connection lifetimes. An HTTP server using a combination of shared_ptr's and weak_ptr's can be found here: via-httplib.

The HTTP server is built upon an asynchronous TCP server which uses a collection of (shared_ptr's to) connections, created on connects and destroyed on disconnects as you propose.

Original Thread

By anonymous    2017-09-20

Instead of using an io_service in a thread per pair of network cards, you may be better off wrapping your sockets in an asio::io_service::strand and using a single io_service in a thread pool, see: Strands: Use Threads Without Explicit Locking and Asynchronous IO with boost asio.

It is easiest to put the sockets and strands together in a class as in this example: Timer 5 example. There is some code that supports asio UDP sockets and strands here.

Original Thread

By anonymous    2017-09-20

No, you cannot safely call async_send_to multiple times in a row WITHOUT waiting for the write handler to be called. See Asynchronous IO with Boost.Asio to see precisely why.

However, asio supports scatter gather and so you can call async_send_to with multiple buffers, e.g.:

typedef std::deque<boost::asio::const_buffer> ConstBuffers;

std::string msg_1("Blah");
...
std::string msg_n("Blah");

ConstBuffers buffers;
buffers.push_back(msg_1);
...
buffers.push_back(msg_n);

socket_.async_send_to(buffers, tx_endpoint_, write_handler);

So you could increase your throughput by double buffering your message queue and using gathered writes...

Original Thread

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