[Beowulf] Re: dealing with lots of sockets

Perry E. Metzger perry at piermont.com
Thu Jul 3 13:59:06 EDT 2008


Bogdan Costescu <Bogdan.Costescu at iwr.uni-heidelberg.de> writes:
> On Wed, 2 Jul 2008, Perry E. Metzger wrote:
>
>> Event driven programming typically uses registered callbacks that
>> are triggered by a central "Event Loop" when events happen. In such
>> a system, one never blocks for anything -- all activity is performed
>> in callbacks, and one simply returns from a callback if one can't
>> proceed further.
>
> And here is one of the problems that event driven programming can't
> really solve: separation between the central event loop and the code
> to run when events happen.

I don't understand what you mean.

> fork() allows the newly created process to proceed at its own will
> and possibly doing its own mistakes (like buffer overflows) in its
> own address space - the parent process is not affected in any way
> and this allows f.e. daemons to run their core loop with
> administrative priviledges while the real work can be done as a dumb
> user.

Oh, that's not an issue at all. For example, say you wanted to run an
SMTP daemon as a pure event app but you don't want it to run as
root. So, you're screwed because you can't open port 25 as a normal
user, right? Well, you can either change privs after opening 25, or
you can use fd passing to pass open file descriptors between a small
rootly process and the mail processing event driven process.

Anyway, yah, bugs are a problem. If you have a bug in an event driven
system you bring down 10,000 connections at once instead of 1. You
do indeed have to be confident your code doesn't suck.

-- 
Perry E. Metzger		perry at piermont.com
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