What is the difference between synchronous and asynchronous transmission in TCP/ IP socket programming?

multithreading asynchronous tcp network-programming synchronous
abhi abhi picture abhi abhi · Jul 5, 2013 · Viewed 33.3k times · Source

I am new to C++ and I am trying to develop a client-server application based on the boost::asio library. I am (still) not able to understand properly the difference between sync and async modes. I've previously studied web protocol services such as HTTP and AJAX. From this explanation, it's clear that HTTP is synchronous and AJAX is asynchronous. What is the difference in TCP socket communication in terms of sync and async? And which mode is better from the perspective of enterprise-level multi-threaded application development, and why?

As I understand synchronous mode, the client blocks for a while until it receives the packet/ data message from the server. And in async mode, the client carries out another operation without blocking the current operation. Why is this different? Is async synonymous with UDP? It seems it doesn't care if it receives transmission acknowledgement.

Answer

user207421 picture user207421 · Jul 5, 2013

  1. TCP transmission is always asynchronous. What's synchronous or asynchronous is the behaviour of the API. A synchronous API does things while you call it: for example, send() moves data to the TCP send buffer and returns when it is done. An asynchronous API starts when you call it, executes independently after it returns to you, and calls you back or provides an interrogable handle via which completion is notified.

  2. HTTP is synchronous in the sense that you send a request, receive a response, display or process the response, all in that order.

  3. Ajax is asynchronous only in the sense that it operates independently of the page request/response cycle in the surrounding HTTP request. It's a poor choice of terminology. It would have been better to use a term like 'nested', 'out of band', ...

Related questions

How to use the CancellationToken property?

Compared to the preceding code for class RulyCanceler, I wanted to run code using CancellationTokenSource. How do I use it as mentioned in Cancellation Tokens, i.e. without throwing/catching an exception? Can I use the IsCancellationRequested property? I attempted …

Read More
How to create threads in nodejs

Is there any way to create threads for running multiple methods at a time? That way, if any method fails in between all the other threads should be killed.

Read More
How to sleep the thread in node.js without affecting other threads?

As per Understanding the node.js event loop, node.js supports a single thread model. That means if I make multiple requests to a node.js server, it won't spawn a new thread for each request but will execute each …

Read More