On Sat, 23 Apr 2011 19:41:28 -0400
Ken Wesson <[email protected]> wrote:
> > Well, Java servers probably are yes, but traditional Unix servers
> > would normally fork a new process for each incoming connection.
>
> Poor man's threads. Although the insulation of each one against
> crashes in the others might be useful when you're coding in a language
> with memory management tools as primitive as C's. ;)
Or your tools for handling concurrency are as poor as C's (which is
unfortunately most popular languages), or you live in a universe where
cosmic rays can flip bits and other sources of hardware hiccups exist.
> > starting a pool of processes to avoid the startup time of a new process
> > when a new client connects.
>
> With small lightweight C processes and some suitable system for IPC,
> this can work. With JVMs, not so much, unless you have RAM coming out
> of your ears. JVM processes tend to be fairly large; it wouldn't take
> many 64MB java.exe jobs to start the pagefile thrashing. Even with an
> 8GB server, you start paging at 128 simultaneous connections in that
> case, and you certainly can't handle thousands.
I would have expected large chunks of the JVM processes to be shared
between parent and child - especially before the first accept
returns. In particular, the VM implementation and the compiled JVM
bytecodes should all be shared. Data structures & JIT'ed code - well,
it will depend on a variety of implementation details, but they all
start on shared pages with a COW bit set.
Of course, if you're using threads in the parent for other things,
then forking to create new processes creates a bunch of interesting
things to deal with.
<mike
--
Mike Meyer <[email protected]> http://www.mired.org/consulting.html
Independent Software developer/SCM consultant, email for more information.
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