<div dir="ltr"><div><div><div><div>Good Morning!<br><br></div>You can spawn a process with spawn_link or spawn_monitor depending on what you want to use.<br><br></div>Links are bidirectional so if your parent process dies then the worker processes will be affected. If you use process_flag(trap_exit, true) on your parent process, then you will receive a message when a linked process exits. If it crashes you get {'EXIT', From, Why} or if it exits normally you get {'EXIT', From, normal}. If you don't use process_flag(trap_exit, true) and let's say a worker process dies, then the links would cascade the exit to the parent and all of the workers.<br>
<br></div>Monitors are one-way. If your monitor process crashes you get the message {'DOWN', Ref, process, Who, Reason} and if it exits normally you get {'DOWN', Ref, process, Who, normal}. There can be nested monitors between processes so watch out if you do not use spawn_monitor but rather setup the monitor later with erlang:monitor/2.<br>
<br></div><div>Aggelos<br></div></div><div class="gmail_extra"><br><br><div class="gmail_quote">On Sun, Nov 17, 2013 at 6:43 AM, akonsu <span dir="ltr"><<a href="mailto:akonsu@gmail.com" target="_blank">akonsu@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">thanks everyone for your help. it is clearer now.<div><br></div><div>I decided to just count my processes to make sure that I do not start more than some maximum number.</div>
<div><br></div><div>I have one more question. Are monitors designed to be used efficiently with a lot of very short lived processes? Are monitors inexpensive to set up? Is this a normal erlang programming practice to use monitors for a lot of short lived processes? Alternatively, I believe I can use spawn_linked to start my processes, and send a message from each worker, when the worker finishes (since otherwise I would only get a message if a linked process crashes). How does this latter approach compare to using monitors?</div>
<div><br></div><div>thanks for help</div><div>konstantin</div><div><br></div></div><div class="HOEnZb"><div class="h5"><div class="gmail_extra"><br><br><div class="gmail_quote">2013/11/15 akonsu <span dir="ltr"><<a href="mailto:akonsu@gmail.com" target="_blank">akonsu@gmail.com</a>></span><br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">Hello,<div><br></div><div>I am looking for an advice on how to architect my system. I am just a beginner...</div>
<div><br></div><div>I have a process that receives messages and this process needs to parse each message, extract some information from the parsed message, and then send this information to the subscribers.</div>
<div><br></div><div>As I read somewhere, in a situation like this, people usually spawn a worker process per message, and let this worker do the work, and then send the results to the publishers.</div><div><br></div><div>
I have an overwhelming amount of incoming messages (these are tweets that I get from a twitter stream), and I am not experienced enough to be able to tell whether this worker-per-task approach is the right way to do it. I am afraid that my application will be flooded with workers and eventually can collapse.</div>
<div><br></div><div>I was thinking that maybe I can use a worker process pool? A process pool seems unusual in an Erlang application, does it not? Although the "Learn yourself Erlang..." does have a chapter on building a pool like this.</div>
<div><br></div><div>Or maybe rate-limit the number of incoming messages?</div><div><br></div><div>I would really appreciate an advice or two.</div><div><br></div><div>Thank you</div><div>Konstantin</div><div><br></div></div>
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