CODEWITHSUNDEEP
c++clinuxnetwork-programmingscheduling
Sadeq Dousti
Sadeq Dousti

Reputation: 3526

Scheduling Packet Retransmission

I'm programming a network protocol over UDP, using C/C++ in Linux. The protocol must provide reliability, so I'm going to simulate something like TCP retransmission over UDP.

This can be done using pthreads or fork, but I believe that's an overkill and consumes a lot of system resources. A better approach is to exploit a scheduler.

I probably can't use Linux internal scheduler, since I'm programming in user space. Are there standard C/C++ libraries to accomplish this? How about 3rd party libraries?

Edit: Some people asked why I'm doing this. Why not use the TCP instead?

The answer is, since I'm implementing a tunneling protocol. If someone tunnels TCP over TCP, the efficiency will drop considerably. Here's more info Why TCP Over TCP Is A Bad Idea.

Upvotes: 3

Views: 1166

Answers (3)

MK.
MK.

Reputation: 34527

Not clear what exactly you are trying to schedule. You can use libevent for efficient and somewhat portable interface. This is basically similar to Matthew's suggestion of using select, but using the most efficient interface (which select is not) on FreeBSD, Linux and MacOS X (actually their page now claims Windows support as well but I'm not too familiar with that). This will give ability to do non-blocking event-driven network calls. It will not solve the scheduling part. DOing it in a separate thread is not going to hurt your performance. I think running a pthread per connection is not the best approach, but having a single scheduling thread and some worker threads dealing with the network events and maybe some non-trivial processing usually works well.

Upvotes: 1

SilverbackNet
SilverbackNet

Reputation: 2074

Here's a sample of how to accomplish asynchronous coroutines with Boost. Boost manages the overhead of creating a thread to run the coroutine in this case so that you don't need to. If you would like the kernel to manage your interrupts, you can use alarm & setitimer, but they're very limited in what they can do.

Any solution will include threads, forks, or some variant of them at some level, unless you synchronously manage the transmission in the main thread using something like select().

Upvotes: 1

Matthew Herrmann
Matthew Herrmann

Reputation: 432

The "scheduler" you're after is called "select", and it's a user-space call available in linux. Type "man 2 select" to read the help page for how to use it.

If you need a timeout, just call select() with a timeout value. The select call will return either when new data has arrived, or a timeout has expired. You can then do retransmissions if there was a timeout.

Upvotes: 5

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