I'm trying to implement a pool of workers in Go. The go-wiki (and Effective Go in the Channels section) feature excellent examples of bounding resource use. Simply make a channel with a buffer that's as large as the worker pool. Then fill that channel with workers, and send them back into the channel when they're done. Receiving from the channel blocks until a worker is available. So the channel and a loop is the entire implementation -- very cool!
Alternatively one could block on sending into the channel, but same idea.
My question is about changing the size of the worker pool while it's running. I don't believe there's a way to change the size of a channel. I have some ideas, but most of them seem way too complicated. This page actually implements a semaphore using a channel and empty structs in much the same way, but it has the same problem (these things come up all the time while Googling for "golang semaphore".
I would do it the other way round. Instead of spawning many goroutines (which still require a considerable amount of memory) and use a channel to block them, I would model the workers as goroutines and use a channel to distribute the work. Something like this:
It might be a good idea to create a separate WorkerPool type with some convenient methods. Also, instead of
type Task string
it is quite common to use a struct that also contains adone
channel that is used to signal that the task had been executed successfully.Edit: I've played around a bit more and came up with the following: http://play.golang.org/p/VlEirPRk8V. It's basically the same example, with a nicer API.