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    <p>Ahh yes... the dangers of "We should do more of this" without explaining what each of those do and in what circumstances you'd use them. For something like <code>delayed_job</code> you may even be using <code>fork</code> without knowing that you're using <code>fork</code>. That said, it really doesn't matter. Ryan was talking about using <code>fork</code> for preforking servers. <code>delayed_job</code> would use <code>fork</code> for turning a process into a daemon. Same system call, different purposes. Running <code>delayed_job</code> in the foreground (without <code>fork</code>) vs in the background (with <code>fork</code>) will result in a negligible performance difference.</p> <p>However, if you write a server that accepts concurrent connections, now Ryan's advice is right on the money.</p> <ul> <li><code>fork</code>: creates a copy of the original process</li> <li><code>execve</code>: stops executing the current file and begins executing a new file in the same process (very useful in rake tasks)</li> <li><code>pipe</code>: creates a pipe (two file descriptors, one for read, one for write)</li> <li><code>socketpair</code>: like a pipe, but for sockets</li> <li><code>select</code>: let's you wait for one or more of multiple file descriptors to be ready with a timeout</li> <li><code>kill</code>: used to send a signal to a process</li> <li><code>sigaction</code>: lets you change what happens when a process receives a signal</li> </ul>
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    1. COSo instead of creating a (green) Thread, I could use fork(2) instead and git a PID back. This much I have done. How do I work with the block for trap('USR1') which wakes up the thread when I new job hits the queue? How would I create more then one process and get them to pull off the queue optimally. The magic seems to be in pipe and select but I don't understand the intricacies. I can use the daemon gem to create a daemon process which uses fork under the hood. I want to start some child processes to run the queue.
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      1. USJohn F. Miller
    2. CODepends on what "work" means in this context. If "work" is I/O, it might be different and yeah, `select` is important. I prefer to design work queues in such a way that work can be executed in any order. So if work unit #1 gets executed concurrently with work unit #2, that's not an issue. As for the daemons gem... I used to use it, but now I either use `fork` directly or I use my ChainGang library. I found that daemons hid too much important stuff, and it was unnecessary overhead for something that's actually not that hard. Note that ChainGang is very alpha quality.
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    3. COEssentially, worrying about "pulling off the queue optimally" doesn't make a whole lot of sense in most contexts. Either you're working with I/O, in which case you're probably not using a `delayed_job` queue, or you are executing things as discrete work units, in which case `select` and `pipe` don't make any sense. Either way, the right way to deal with a work queue is to just grab whatever's on top whenever you're free. And if there's nothing there, it's probably OK to just block until there is.
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