On Fri, 2004-11-05 at 13:39, Larsen, Errin M HMMA/IT wrote: > > -----Original Message----- > > From: JupiterHost.Net [mailto:[EMAIL PROTECTED] > > Sent: Friday, November 05, 2004 3:08 PM > > To: [EMAIL PROTECTED] > > Cc: Jose Nyimi > > Subject: Re: RE : start http request and move on > > > > > > > > > Nice approach, I have learned today an easy to do it :) Though care > > > should be taken to not fork many *uncontrolled* childs. > > > > Could you elaborate what uncontrolled children are > > specifically and what > > should be avoided? > > (In context of this thread of course not the little humans running > > around like crazy ;p) > > > > > Rgds, > > > JosÃ. > > > > -- > > Hi, > > I've been lurking on this thread for a bit, and now that you've jumped to children > and fork and related topics I'll chime in! > > I found a lot of useful information about this sort of thing in "perldoc perlipc". > Check out the stuff about Daemons and the REAPER subroutine in that doc. Also, in > the cookbook (I think! I don't have it with me to check) there is some good stuff > about daemons and children. > > More specifically to the questions above, two things to be careful of: > > First, always, ALWAYS check (then, check again!) that you are not going to fork-bomb > your system. If your script, forks (now you have 2), then both of those fork again, > 'cause you have a bug in a loop somewhere (now you have 4) and so on (now there are > 8) and so on (16 ... Can you see where this is goin?!), you will quickly bring your > box to a screaching halt! > > Second, (I'm assuming this is a UNIX-ey OS) make sure you read up on setsid and > sys_wait_h in the POSIX (perldoc POSIX) module, as well as the builtin 'waitpid' > (perldoc -f waitpid). You might have to 'man' the equivelant to get meaningful > documentation (like, 'man setsid'). > > When I fork a process, I like to make sure the child at least does the following: > - chdir / > (it's rude for a random process to sit on a filesystem that might need to be > unmounted) > - change the stdin, stdout and stderr > (also rude to spurt random nonsense from a random process onto the terminal or > somesuch) > - setsid > (So the child can own it's own session) > > Like this: > > sub daemonize { > chdir '/' or die "Can't chdir to /: $!"; > open STDIN, '/dev/null' or die "Can't read /dev/null: $!"; > open STDOUT, '/dev/null' or die "Can't write to /dev/null: $!"; > > defined( my $pid = fork ) or die "Can't fork the child: $!"; > > #The exit below can be replaced with an if-else construct if you want the > original to keep going. > #I believe this has been handled in this thread already! > exit if $pid; # original process dies here > setsid or die "Can't start a new session: $!"; > open STDERR, '>&STDOUT' or die "Can't duplicate STDOUT: $!"; > } > > I hope this helps a bit. Let me know if ya got more questions, > > --Errin
when you do want to code a daemon, you also might take a look at Proc::Daemon which does most, if not all, of what the code above does. --Christopher -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] <http://learn.perl.org/> <http://learn.perl.org/first-response>
