Writing a server that queues tasks

I'm writing a server in python that needs to take requests from clients, queue the requests, execute them one at a time, then tell the clients that their particular request has been processed.

Currently the way I've approached it is using a TCP socket server -- however, I'm not sure how to make it so that only one request is being executed at a time from a queue?

The way I would like for it to look:

Client1 -> (a) -> Server
Client2 -> (b) -> Server
Client3 -> (c) -> Server

Server makes queue |a, b, c|
Execute a first. Done? Tell Client 1
Execute b second. Done? Tell Client 2
Execute c third. Done? Tell Client 3

From what I understand, if I have the server recv the client's request, execute it, and respond, that may happen at the same time in different threa开发者_开发百科ds. I only want one thread executing all the tasks (because I anticipate many tasks coming in and it'd be slow if everyone was running one at the same time). How do I accomplish that?

---

There are tons of ways to skin it, but a solution is going to look something like the below:

Client -> Client-Mediator (TCP Port) <--> Server Mediator -> (ServerQ) <- Task Process

The flow would be like this:

Client Process:

1. Client creates a client mediator on a tcp socket.
2. Sends whatever info it needs over the port.
3. Server Mediator receives the request
   1. Creates a response Q for the Task Process
   2. Places the request on the Server Q (command + responseQ)
4. Wait for response on responseQ
   1. No response after X time timeout ?
   2. Once response comes, read and send response over tcp port.

Server Process:

1. Reads from Server Q.
   1. Processes command
   2. Write the response to the response Q

---

Components involved

Client - Simple process that sends requests for tasks to be completed.

Client-Mediator - Creates a connection to the server process.

Server-Mediator - Accepts a client request for task processing, enqueues tasks and waits for response.

Task Process - Reads from ServerQ and waits for a task to come in.

---

Okay so what Nix said was right but I wasn't sure how to make that exactly happen (my question was how to go about actually making this)

As it turns out I had to start 2 threads: one that executes from the queue, and the other being the main server handler. The server handler spawns threads for each new connection, and the client blocks after sending a request / if the request is successfully queued. This means that the queue needs to be thread-safe / protected with a semaphore or mutex. In the case of python, there is a multiprocessing.Queue class that handles that for you. Whenever a task is executed, the execution thread does a notifyAll() which causes all sleeping threads to wake up and check if their requested task is done. I use a condition variable for that.