package Server::Starter;
use 5.008;
use strict;
use warnings;
use Carp;
use Fcntl;
use IO::Handle;
use IO::Socket::INET;
use IO::Socket::UNIX;
use List::MoreUtils qw(uniq);
use POSIX qw(:sys_wait_h);
use Proc::Wait3;
use Scope::Guard;
use Exporter qw(import);
our $VERSION = '0.19';
our @EXPORT_OK = qw(start_server restart_server server_ports);
my @signals_received;
sub start_server {
my $opts = {
(@_ == 1 ? @$_[0] : @_),
};
$opts->{interval} = 1
if not defined $opts->{interval};
$opts->{signal_on_hup} ||= 'TERM';
$opts->{signal_on_term} ||= 'TERM';
$opts->{backlog} ||= Socket::SOMAXCONN();
for ($opts->{signal_on_hup}, $opts->{signal_on_term}) {
# normalize to the one that can be passed to kill
tr/a-z/A-Z/;
s/^SIG//i;
}
# prepare args
my $ports = $opts->{port};
my $paths = $opts->{path};
croak "either of ``port'' or ``path'' option is mandatory\n"
unless $ports || $paths;
$ports = [ $ports ]
if ! ref $ports && defined $ports;
$paths = [ $paths ]
if ! ref $paths && defined $paths;
croak "mandatory option ``exec'' is missing or is not an arrayref\n"
unless $opts->{exec} && ref $opts->{exec} eq 'ARRAY';
# set envs
$ENV{ENVDIR} = $opts->{envdir}
if defined $opts->{envdir};
$ENV{ENABLE_AUTO_RESTART} = $opts->{enable_auto_restart}
if defined $opts->{enable_auto_restart};
$ENV{KILL_OLD_DELAY} = $opts->{kill_old_delay}
if defined $opts->{kill_old_delay};
$ENV{AUTO_RESTART_INTERVAL} = $opts->{auto_restart_interval}
if defined $opts->{auto_restart_interval};
# open pid file
my $pid_file_guard = sub {
return unless $opts->{pid_file};
open my $fh, '>', $opts->{pid_file}
or die "failed to open file:$opts->{pid_file}: $!";
print $fh "$$\n";
close $fh;
return Scope::Guard->new(
sub {
unlink $opts->{pid_file};
},
);
}->();
# open log file
if ($opts->{log_file}) {
open my $fh, '>>', $opts->{log_file}
or die "failed to open log file:$opts->{log_file}: $!";
STDOUT->flush;
STDERR->flush;
open STDOUT, '>&', $fh
or die "failed to dup STDOUT to file: $!";
open STDERR, '>&', $fh
or die "failed to dup STDERR to file: $!";
close $fh;
}
# create guard that removes the status file
my $status_file_guard = $opts->{status_file} && Scope::Guard->new(
sub {
unlink $opts->{status_file};
},
);
print STDERR "start_server (pid:$$) starting now...\n";
# start listening, setup envvar
my @sock;
my @sockenv;
for my $port (@$ports) {
my $sock;
if ($port =~ /^\s*(\d+)\s*$/) {
$sock = IO::Socket::INET->new(
Listen => $opts->{backlog},
LocalPort => $port,
Proto => 'tcp',
ReuseAddr => 1,
);
} elsif ($port =~ /^\s*(.*)\s*:\s*(\d+)\s*$/) {
$port = "$1:$2";
$sock = IO::Socket::INET->new(
Listen => $opts->{backlog},
LocalAddr => $port,
Proto => 'tcp',
ReuseAddr => 1,
);
} else {
croak "invalid ``port'' value:$port\n"
}
die "failed to listen to $port:$!"
unless $sock;
fcntl($sock, F_SETFD, my $flags = '')
or die "fcntl(F_SETFD, 0) failed:$!";
push @sockenv, "$port=" . $sock->fileno;
push @sock, $sock;
}
my $path_remove_guard = Scope::Guard->new(
sub {
-S $_ and unlink $_
for @$paths;
},
);
for my $path (@$paths) {
if (-S $path) {
warn "removing existing socket file:$path";
unlink $path
or die "failed to remove existing socket file:$path:$!";
}
unlink $path;
my $saved_umask = umask(0);
my $sock = IO::Socket::UNIX->new(
Listen => $opts->{backlog},
Local => $path,
) or die "failed to listen to file $path:$!";
umask($saved_umask);
fcntl($sock, F_SETFD, my $flags = '')
or die "fcntl(F_SETFD, 0) failed:$!";
push @sockenv, "$path=" . $sock->fileno;
push @sock, $sock;
}
$ENV{SERVER_STARTER_PORT} = join ";", @sockenv;
$ENV{SERVER_STARTER_GENERATION} = 0;
# setup signal handlers
$SIG{$_} = sub {
push @signals_received, $_[0];
} for (qw/INT TERM HUP ALRM/);
$SIG{PIPE} = 'IGNORE';
# setup status monitor
my ($current_worker, %old_workers, $last_restart_time);
my $update_status = $opts->{status_file}
? sub {
my $tmpfn = "$opts->{status_file}.$$";
open my $tmpfh, '>', $tmpfn
or die "failed to create temporary file:$tmpfn:$!";
my %gen_pid = (
($current_worker
? ($ENV{SERVER_STARTER_GENERATION} => $current_worker)
: ()),
map { $old_workers{$_} => $_ } keys %old_workers,
);
print $tmpfh "$_:$gen_pid{$_}\n"
for sort keys %gen_pid;
close $tmpfh;
rename $tmpfn, $opts->{status_file}
or die "failed to rename $tmpfn to $opts->{status_file}:$!";
} : sub {
};
# setup the start_worker function
my $start_worker = sub {
my $pid;
while (1) {
$ENV{SERVER_STARTER_GENERATION}++;
$pid = fork;
die "fork(2) failed:$!"
unless defined $pid;
if ($pid == 0) {
my @args = @{$opts->{exec}};
# child process
if (defined $opts->{dir}) {
chdir $opts->{dir} or die "failed to chdir:$!";
}
{ exec { $args[0] } @args };
print STDERR "failed to exec $args[0]$!";
exit(255);
}
print STDERR "starting new worker $pid\n";
sleep $opts->{interval};
if ((grep { $_ ne 'HUP' } @signals_received)
|| waitpid($pid, WNOHANG) <= 0) {
last;
}
print STDERR "new worker $pid seems to have failed to start, exit status:$?\n";
}
# ready, update the environment
$current_worker = $pid;
$last_restart_time = time;
$update_status->();
};
# setup the wait function
my $wait = sub {
my $block = @signals_received == 0;
my @r;
if ($block && $ENV{ENABLE_AUTO_RESTART}) {
alarm(1);
@r = wait3($block);
alarm(0);
} else {
@r = wait3($block);
}
return @r;
};
# setup the cleanup function
my $cleanup = sub {
my $sig = shift;
my $term_signal = $sig eq 'TERM' ? $opts->{signal_on_term} : 'TERM';
$old_workers{$current_worker} = $ENV{SERVER_STARTER_GENERATION};
undef $current_worker;
print STDERR "received $sig, sending $term_signal to all workers:",
join(',', sort keys %old_workers), "\n";
kill $term_signal, $_
for sort keys %old_workers;
while (%old_workers) {
if (my @r = wait3(1)) {
my ($died_worker, $status) = @r;
print STDERR "worker $died_worker died, status:$status\n";
delete $old_workers{$died_worker};
$update_status->();
}
}
print STDERR "exiting\n";
};
# the main loop
$start_worker->();
while (1) {
# wait for next signal (or when auto-restart becomes necessary)
my @r = $wait->();
# reload env if necessary
my %loaded_env = _reload_env();
my @loaded_env_keys = keys %loaded_env;
local @ENV{@loaded_env_keys} = map { $loaded_env{$_} } (@loaded_env_keys);
$ENV{AUTO_RESTART_INTERVAL} ||= 360
if $ENV{ENABLE_AUTO_RESTART};
# restart if worker died
if (@r) {
my ($died_worker, $status) = @r;
if ($died_worker == $current_worker) {
print STDERR "worker $died_worker died unexpectedly with status:$status, restarting\n";
$start_worker->();
} else {
print STDERR "old worker $died_worker died, status:$status\n";
delete $old_workers{$died_worker};
$update_status->();
}
}
# handle signals
my $restart;
while (@signals_received) {
my $sig = shift @signals_received;
if ($sig eq 'HUP') {
print STDERR "received HUP, spawning a new worker\n";
$restart = 1;
last;
} elsif ($sig eq 'ALRM') {
# skip
} else {
return $cleanup->($sig);
}
}
if (! $restart && $ENV{ENABLE_AUTO_RESTART}) {
my $auto_restart_interval = $ENV{AUTO_RESTART_INTERVAL};
my $elapsed_since_restart = time - $last_restart_time;
if ($elapsed_since_restart >= $auto_restart_interval && ! %old_workers) {
print STDERR "autorestart triggered (interval=$auto_restart_interval)\n";
$restart = 1;
} elsif ($elapsed_since_restart >= $auto_restart_interval * 2) {
print STDERR "autorestart triggered (forced, interval=$auto_restart_interval)\n";
$restart = 1;
}
}
# restart if requested
if ($restart) {
$old_workers{$current_worker} = $ENV{SERVER_STARTER_GENERATION};
$start_worker->();
print STDERR "new worker is now running, sending $opts->{signal_on_hup} to old workers:";
if (%old_workers) {
print STDERR join(',', sort keys %old_workers), "\n";
} else {
print STDERR "none\n";
}
my $kill_old_delay = defined $ENV{KILL_OLD_DELAY} ? $ENV{KILL_OLD_DELAY} : $ENV{ENABLE_AUTO_RESTART} ? 5 : 0;
if ($kill_old_delay != 0) {
print STDERR "sleeping $kill_old_delay secs before killing old workers\n";
sleep $kill_old_delay;
}
print STDERR "killing old workers\n";
kill $opts->{signal_on_hup}, $_
for sort keys %old_workers;
}
}
die "unreachable";
}
sub restart_server {
my $opts = {
(@_ == 1 ? @$_[0] : @_),
};
die "--restart option requires --pid-file and --status-file to be set as well\n"
unless $opts->{pid_file} && $opts->{status_file};
# get pid
my $pid = do {
open my $fh, '<', $opts->{pid_file}
or die "failed to open file:$opts->{pid_file}:$!";
my $line = <$fh>;
chomp $line;
$line;
};
# function that returns a list of active generations in sorted order
my $get_generations = sub {
open my $fh, '<', $opts->{status_file}
or die "failed to open file:$opts->{status_file}:$!";
uniq sort { $a <=> $b } map { /^(\d+):/ ? ($1) : () } <$fh>;
};
# wait for this generation
my $wait_for = do {
my @gens = $get_generations->()
or die "no active process found in the status file";
pop(@gens) + 1;
};
# send HUP
kill 'HUP', $pid
or die "failed to send SIGHUP to the server process:$!";
# wait for the generation
while (1) {
my @gens = $get_generations->();
last if scalar(@gens) == 1 && $gens[0] == $wait_for;
sleep 1;
}
}
sub server_ports {
die "no environment variable SERVER_STARTER_PORT. Did you start the process using server_starter?",
unless $ENV{SERVER_STARTER_PORT};
my %ports = map {
+(split /=/, $_, 2)
} split /;/, $ENV{SERVER_STARTER_PORT};
\%ports;
}
sub _reload_env {
my $dn = $ENV{ENVDIR};
return if !defined $dn or !-d $dn;
my $d;
opendir($d, $dn) or return;
my %env;
while (my $n = readdir($d)) {
next if $n =~ /^\./;
open my $fh, '<', "$dn/$n" or next;
chomp(my $v = <$fh>);
$env{$n} = $v if defined $v;
}
return %env;
}
1;
__END__
=head1 NAME
Server::Starter - a superdaemon for hot-deploying server programs
=head1 SYNOPSIS
# from command line
% start_server --port=80 my_httpd
# in my_httpd
use Server::Starter qw(server_ports);
my $listen_sock = IO::Socket::INET->new(
Proto => 'tcp',
);
$listen_sock->fdopen((values %{server_ports()})[0], 'w')
or die "failed to bind to listening socket:$!";
while (1) {
if (my $conn = $listen_sock->accept) {
....
}
}
=head1 DESCRIPTION
It is often a pain to write a server program that supports graceful restarts, with no resource leaks. L<Server::Starter> solves the problem by splitting the task into two. One is L<start_server>, a script provided as a part of the module, which works as a superdaemon that binds to zero or more TCP ports or unix sockets, and repeatedly spawns the server program that actually handles the necessary tasks (for example, responding to incoming commenctions). The spawned server programs under L<Server::Starter> call accept(2) and handle the requests.
To gracefully restart the server program, send SIGHUP to the superdaemon. The superdaemon spawns a new server program, and if (and only if) it starts up successfully, sends SIGTERM to the old server program.
By using L<Server::Starter> it is much easier to write a hot-deployable server. Following are the only requirements a server program to be run under L<Server::Starter> should conform to:
- receive file descriptors to listen to through an environment variable
- perform a graceful shutdown when receiving SIGTERM
A Net::Server personality that can be run under L<Server::Starter> exists under the name L<Net::Server::SS::PreFork>.
=head1 METHODS
=over 4
=item server_ports
Returns zero or more file descriptors on which the server program should call accept(2) in a hashref. Each element of the hashref is: (host:port|port|path_of_unix_socket) => file_descriptor.
=item start_server
Starts the superdaemon. Used by the C<start_server> script.
=back
=head1 AUTHOR
Kazuho Oku
=head1 SEE ALSO
L<Net::Server::SS::PreFork>
=head1 LICENSE
This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
=cut