Multithreaded Server Issue

Question

I am writing a server in linux that is supposed to serve an API.

Initially, I wanted to make it Multi-threaded on a single port, meaning that I'd have multiple threads working on various request received on a single port.

One of my friends told me that it not the way it is supposed to work. He told me that when a request is received, I first have to follow a Handshake procedure, create a thread that is listening to some other port dedicated to the request and then redirect the requested client to the new port.

Theoretically, it's very interesting but I could not find any information on how to implement the handshake and do the redirection. Can someone help?

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If I'm not wrong in interpreting your responses, once I create a multithreaded server with a main thread listening to a port, and creates a new thread to handle requests, I'm essentially making it multithreaded on a single port?

Consider the scenario where I get a large number of requests every second. Isn't it true that every request on the port should now wait for the "current" request to complete? If not, how would the communication still be done: Say a browser sends a request, so the thread handling this has to first listen to the port, block it, process it, respond and then unblock it.

By this, eventhough I'm having "multithreads" , all I'm using is one single thread at a time apart from the main thread because the port is being blocked.

Answer 1

TCP/IP does the handshake, if you can't think of any reason to do a handshake than your application does not demand it.

An example of an application specific handshake could be for user authentication.

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What your colleague is suggesting sounds like the way FTP works. This is not a good thing to do -- the internet these days is more or less used for protocols which use a single port, and having a command port is bad. One of the reasons is because statefull firewalls aren't designed for multi-port applications; they have to be extended for each individual application that does things this way.

Answer 2

What your friend told you is similar to passive FTP - a client tells the server that it needs a connection, the server sends back the port number and the client creates a data connection to that port.

But all you wanted to do is a multithreaded server. All you need is one server socket listening and accepting connections on a given port. As soon as the automatic TCP handshake is finished, you'll get a new socket from the accept function - that socket will be used for communication with the client that has just connected. So now you only have to create a new thread, passing that client socket to the thread function. In your server thread, you will then call accept again in order to accept another connection.

Answer 3

Look at ASIO's tutorial on async TCP. There one part accept connections on TCP and spawns handlers that each communicate with a single client. That's how TCP-servers usually work (including HTTP/web, the most common tcp protocol.)

You may disregard the asynchronous stuff of ASIO if you're set on creating a thread per connection. It doesn't apply to your question. (Going fully async and have one worker-thread per core is nice, but it might not integrate well with the rest of your environment.)