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17.12. Pre-Forking ServersProblemYou want to write a server that concurrently processes several clients (as in "Forking Servers"), but connections are coming in so fast that forking slows the server too much. SolutionHave a master server maintain a pool of pre-forked children, as shown in Example 17.5. Example 17.5: preforker#!/usr/bin/perl # preforker - server who forks first use IO::Socket; use Symbol; use POSIX; # establish SERVER socket, bind and listen. $server = IO::Socket::INET->new(LocalPort => 6969, Type => SOCK_STREAM, Proto => 'tcp', Reuse => 1, Listen => 10 ) or die "making socket: $@\n"; # global variables $PREFORK = 5; # number of children to maintain $MAX_CLIENTS_PER_CHILD = 5; # number of clients each child should process %children = (); # keys are current child process IDs $children = 0; # current number of children sub REAPER { # takes care of dead children $SIG{CHLD} = \&REAPER; my $pid = wait; $children --; delete $children{$pid}; } sub HUNTSMAN { # signal handler for SIGINT local($SIG{CHLD}) = 'IGNORE'; # we're going to kill our children kill 'INT' => keys %children; exit; # clean up with dignity } # Fork off our children. for (1 .. $PREFORK) { make_new_child(); } # Install signal handlers. $SIG{CHLD} = \&REAPER; $SIG{INT} = \&HUNTSMAN; # And maintain the population. while (1) { sleep; # wait for a signal (i.e., child's death) for ($i = $children; $i < $PREFORK; $i++) { make_new_child(); # top up the child pool } } sub make_new_child { my $pid; my $sigset; # block signal for fork $sigset = POSIX::SigSet->new(SIGINT); sigprocmask(SIG_BLOCK, $sigset) or die "Can't block SIGINT for fork: $!\n"; die "fork: $!" unless defined ($pid = fork); if ($pid) { # Parent records the child's birth and returns. sigprocmask(SIG_UNBLOCK, $sigset) or die "Can't unblock SIGINT for fork: $!\n"; $children{$pid} = 1; $children++; return; } else { # Child can *not* return from this subroutine. $SIG{INT} = 'DEFAULT'; # make SIGINT kill us as it did before # unblock signals sigprocmask(SIG_UNBLOCK, $sigset) or die "Can't unblock SIGINT for fork: $!\n"; # handle connections until we've reached $MAX_CLIENTS_PER_CHILD for ($i=0; $i < $MAX_CLIENTS_PER_CHILD; $i++) { $client = $server->accept() or last; # do something with the connection } # tidy up gracefully and finish # this exit is VERY important, otherwise the child will become # a producer of more and more children, forking yourself into # process death. exit; } } DiscussionWhew. Although this is a lot of code, the logic is simple: the parent process never deals with clients but instead forks The code is a reasonably direct implementation of the logic above. The only trick comes with signal handlers: we want the parent to catch SIGINT and kill its children, so we install our signal handler When you use this code in your programs, be sure that On some operating systems, notably Solaris, you cannot have multiple children doing an See AlsoThe
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