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    <p>I have used perl's "threads" on several occasions. They're most useful for launching some process and continuing on with something else. I don't have a lot of experience in the theory of how they work under the hood, but I do have a lot of practical coding experience with them.</p> <p>For example, I have a server thread that listens for incoming network connections and spits out a status response when someone asks for it. I create that thread, then move on and create another thread that monitors the system, checking five items, sleeping a few seconds, and looping again. It might take 3-4 seconds to collect the monitor data, then it gets shoved into a shared variable, and the server thread can read that when needed and immediately return the last known result to whomever asks. The monitor thread, when it finds that an item is in a bad state, kicks off a separate thread to repair that item. Then it moves on, checking the other items while the bad one is repaired, and kicking off other threads for other bad items or joining finished repair threads. The main program all the while is looping every few seconds, making sure that the monitor and server threads aren't joinable/still running. All of this could be written as a bunch of separate programs utilizing some other form of IPC, but perl's threads make it simple.</p> <p>Another place where I've used them is in a fractal generator. I would split up portions of the image using some algorithm and then launch as many threads as I have CPUs to do the work. They'd each stuff their results into a single GD object, which didn't cause problems because they were each working on different portions of the array, and then when done I'd write out the GD image. It was my introduction to using perl threads, and was a good introduction, but then I rewrote it in C and it was two orders of magnitude faster :-). Then I rewrote my perl threaded version to use Inline::C, and it was only 20% slower than the pure C version. Still, in most cases where you'd want to use threads due to being CPU intensive, you'd probably want to just choose another language.</p> <p>As mentioned by others, fork and threads really overlap for a lot of purposes. Coro, however, doesn't really allow for multi-cpu use or parallel processing like fork and thread do, you'll only ever see your process using 100%. I'm over-simplifying this, but I think the easiest way to describe Coro is that it's a scheduler for your subroutines. If you have a subroutine that blocks you can hop to another and do something else while you wait, for example of you have an app that calculates results and writes them to a file. One block might calculate results and push them into a channel. When it runs out of work, another block starts writing them to disk. While that block is waiting on disk, the other block can start calculating results again if it gets more work. Admittedly I haven't done much with Coro; it sounds like a good way to speed some things up, but I'm a bit put off by not being able to do two things at once.</p> <p>My own personal preference if I want to do multiprocessing is to use fork if I'm doing lots of small or short things, threads for a handful of large or long-lived things.</p>
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