What are Asynchronous Operations and Agents in Asio?

Asynchronous Operations

The Asio asynchronous model promotes asynchronous operations as the fundamental composition. They are the basic unit and represent the background work except for the user’s code which can carry on with other tasks. They support many approaches like callbacks, fibers, futures (eager and lazy), and many others. These approaches help the programmers to choose the best approach for the trade-offs.

Let’s understand the functioning of the life cycle of an asynchronous operation. 

Also read, Abstract Data Types in C++ and Application of Oops

The Life Cycle of an Asynchronous Operation 

The asynchronous operations overall are divided into two phases. Let’s see both phases with the events of the operation.

Phase-1

This phase starts with the call of the initiating function to the asynchronous operation; the operation is in the outstanding stage. 

Phase-2 

Phase 2 begins when the queueing of the completion handler is completed for the execution. When the asynchronous operation is completed, the resultant is displayed by the completion handler.

Initiating Function and Completion Handler

We have used the terms initiating function and the completion handler in the life cycle; these two are the important functions that are present in the user’s code. Refer to the following image.

Initiating Function

The initiating function is a function that can be called by the user to invoke the asynchronous operation.

Completion Handler

A completion handler is a function object that is provided by the user, which can be invoked only once to get the output of the asynchronous operation. 

Inheritance from Synchronous Operation

Many properties of asynchronous operations are inherited from the synchronous operation. These semantic properties improve flexibility and enhance the composition. Let’s look at the properties of synchronous operations and equivalent properties of asynchronous operations.

Now let’s move on to the next section, Asynchronous agents.

Asynchronous Agents

An asynchronous agent comprises asynchronous operations. These agents work collectively with other agents, and every asynchronous operation belongs to the agent. The asynchronous agents might also contain only one operation. Just like threads are for synchronous operations, here, asynchronous agents are for asynchronous operations.

Let’s understand, with a flowchart, what are the associated characteristics of asynchronous agents that are used by asynchronous operations.

The asynchronous agent does not require a concrete mechanism; it is completely based on the imaginary construct, which provides the construct and the composition of the asynchronous operation. The asynchronous agents run the completion handler after the asynchronous operation is completed. These are just the smaller units of the work that needs to be scheduled, which is done by asynchronous agents after waiting for the asynchronous operation to end. This can be better understood by this figure.

Let’s understand asynchronous operations better with the help of an example. 

Implementation of Asynchronous Operation

#include <iostream>
#include <asio.hpp>

using namespace std;

void print(const asio::error_code& /*e*/)
{
    cout << "Hello, Ninjas!!" << std::endl;
}

int main()
{
    asio::io_context io;

    asio::steady_timer t(io, asio::chrono::seconds(5));

    t.async_wait(&print);

    std::cout << "This statement is printed before the function call and we know async_wait() returns immediately.\nThis confirms async_wait() is non-blocking call!\n";

    io.run();

    return 0;
}

You can also try this code with Online C++ Compiler

Run Code

Explanation

We have shown the use of the asynchronous operation async_wait() in this example. In the Asio library, the function async_wait() is used to wait till the completion of an asynchronous operation. The asynchronous operation does not block the execution of any operation if more than one operations are in progress. We have called a function that prints a statement and, after that, another print statement. This second statement will be printed before.

Output

Also see, Abstract Data Types in C++

Frequently Asked Questions

What is Asio?

Asio is a cross-platform, open-source C++ library. It is an underrated C++ library designed for input, output, and networking purposes. Asio stands for asynchronous input-output. Christopher M. Kohlhoff developed Asio in 2003. 

What does asynchronous mean?

Asynchronous means that a process is independent of the execution of any other process. The execution is not blocked for operations if more than one is in progress.

What are the events in the life cycle of asynchronous operations?

The asynchronous operation starts with a call to the initiating function; In this phase, the operation is called outstanding. After this, the completion handler is placed in the queue for execution. The operation is completed, and the results are displayed.

How are asynchronous operations different from synchronous operations?

The operations and programs in asynchronous operations can run in parallel, while the programs in synchronous operations will run one at a time. The asynchronous operations are non-blocking, i.e., they can send more than one request to the server, while the synchronous operation is blocking and can send only one request.

Conclusion

This article was about Asio, which is a C++ library for networking and communication. We have discussed the asynchronous operation and its lifecycle. We have also learned about asynchronous agents and it’s working mechanisms. You can check out our other articles if you want to dive deep into other concepts related to Asio -

👉 Asio Timers 

👉 SSL Support in Asio

👉 TCP, UDP, and ICMP Networking 

You can refer to our guided paths on the Coding Ninjas Studio platform to learn more about DSA, DBMS, Competitive Programming, Python, Java, JavaScript, etc. To practice and improve yourself in the interview, you can also check out Top 100 SQL problems, Interview experience, Coding interview questions, and the Ultimate guide path for interviews. Do upvote our blog to help other ninjas grow.

Happy Coding !!