package Mojo::Server::Prefork;
use Mojo::Base 'Mojo::Server::Daemon';

use Config;
use File::Spec::Functions 'tmpdir';
use Mojo::File 'path';
use Mojo::Util 'steady_time';
use POSIX 'WNOHANG';
use Scalar::Util 'weaken';

has accepts            => 10000;
has cleanup            => 1;
has graceful_timeout   => 120;
has heartbeat_timeout  => 30;
has heartbeat_interval => 5;
has pid_file           => sub { path(tmpdir, 'prefork.pid')->to_string };
has spare              => 2;
has workers            => 4;

sub DESTROY { unlink $_[0]->pid_file if $_[0]->cleanup }

sub check_pid {
  my $file = shift->pid_file;
  return undef unless open my $handle, '<', $file;
  my $pid = <$handle>;
  chomp $pid;

  # Running
  return $pid if $pid && kill 0, $pid;

  # Not running
  unlink $file;
  return undef;
}

sub ensure_pid_file {
  my ($self, $pid) = @_;

  # Check if PID file already exists
  return if -e (my $file = $self->pid_file);

  # Create PID file
  $self->app->log->error(qq{Can't create process id file "$file": $!})
    and die qq{Can't create process id file "$file": $!}
    unless open my $handle, '>', $file;
  $self->app->log->info(qq{Creating process id file "$file"});
  chmod 0644, $handle;
  print $handle "$pid\n";
}

sub healthy {
  scalar grep { $_->{healthy} } values %{shift->{pool}};
}

sub run {
  my $self = shift;

  # No fork emulation support
  say 'Pre-forking does not support fork emulation.' and exit 0
    if $Config{d_pseudofork};

  # Pipe for worker communication
  pipe($self->{reader}, $self->{writer}) or die "Can't create pipe: $!";

  # Clean manager environment
  local $SIG{CHLD} = sub {
    while ((my $pid = waitpid -1, WNOHANG) > 0) {
      $self->emit(reap => $pid)->_stopped($pid);
    }
  };
  local $SIG{INT} = local $SIG{TERM} = sub { $self->_term };
  local $SIG{QUIT} = sub { $self->_term(1) };
  local $SIG{TTIN} = sub { $self->workers($self->workers + 1) };
  local $SIG{TTOU} = sub {
    $self->workers > 0 ? $self->workers($self->workers - 1) : return;
    for my $w (values %{$self->{pool}}) {
      ($w->{graceful} = steady_time) and last unless $w->{graceful};
    }
  };

  # Preload application before starting workers
  $self->start->app->log->info("Manager $$ started");
  $self->ioloop->max_accepts($self->accepts);
  $self->{running} = 1;
  $self->_manage while $self->{running};
  $self->app->log->info("Manager $$ stopped");
}

sub _heartbeat { shift->{writer}->syswrite("$$:$_[0]\n") or exit 0 }

sub _manage {
  my $self = shift;

  # Spawn more workers if necessary and check PID file
  if (!$self->{finished}) {
    my $graceful = grep { $_->{graceful} } values %{$self->{pool}};
    my $spare = $self->spare;
    $spare = $graceful ? $graceful > $spare ? $spare : $graceful : 0;
    my $need = ($self->workers - keys %{$self->{pool}}) + $spare;
    $self->_spawn while $need-- > 0;
    $self->ensure_pid_file($$);
  }

  # Shutdown
  elsif (!keys %{$self->{pool}}) { return delete $self->{running} }

  # Wait for heartbeats
  $self->_wait;

  my $interval = $self->heartbeat_interval;
  my $ht       = $self->heartbeat_timeout;
  my $gt       = $self->graceful_timeout;
  my $log      = $self->app->log;
  my $time     = steady_time;

  for my $pid (keys %{$self->{pool}}) {
    next unless my $w = $self->{pool}{$pid};

    # No heartbeat (graceful stop)
    $log->error("Worker $pid has no heartbeat ($ht seconds), restarting")
      and $w->{graceful} = $time
      if !$w->{graceful} && ($w->{time} + $interval + $ht <= $time);

    # Graceful stop with timeout
    my $graceful = $w->{graceful} ||= $self->{graceful} ? $time : undef;
    $log->info("Stopping worker $pid gracefully ($gt seconds)")
      and (kill 'QUIT', $pid or $self->_stopped($pid))
      if $graceful && !$w->{quit}++;
    $w->{force} = 1 if $graceful && $graceful + $gt <= $time;

    # Normal stop
    $log->warn("Stopping worker $pid immediately")
      and (kill 'KILL', $pid or $self->_stopped($pid))
      if $w->{force} || ($self->{finished} && !$graceful);
  }
}

sub _spawn {
  my $self = shift;

  # Manager
  die "Can't fork: $!" unless defined(my $pid = fork);
  return $self->emit(spawn => $pid)->{pool}{$pid} = {time => steady_time}
    if $pid;

  # Heartbeat messages
  my $loop     = $self->cleanup(0)->ioloop;
  my $finished = 0;
  $loop->on(finish => sub { $finished = 1 });
  weaken $self;
  my $cb = sub { $self->_heartbeat($finished) };
  $loop->next_tick($cb);
  $loop->recurring($self->heartbeat_interval => $cb);

  # Clean worker environment
  $SIG{$_} = 'DEFAULT' for qw(CHLD INT TERM TTIN TTOU);
  $SIG{QUIT} = sub { $loop->stop_gracefully };
  $loop->on(finish => sub { $self->max_requests(1) });
  delete $self->{reader};
  srand;

  $self->app->log->info("Worker $$ started");
  $loop->start;
  exit 0;
}

sub _stopped {
  my ($self, $pid) = @_;

  return unless my $w = delete $self->{pool}{$pid};

  my $log = $self->app->log;
  $log->info("Worker $pid stopped");
  $log->error("Worker $pid stopped too early, shutting down") and $self->_term
    unless $w->{healthy};
}

sub _term {
  my ($self, $graceful) = @_;
  @{$self->emit(finish => $graceful)}{qw(finished graceful)} = (1, $graceful);
}

sub _wait {
  my $self = shift;

  # Poll for heartbeats
  my $reader = $self->emit('wait')->{reader};
  return unless Mojo::Util::_readable(1000, fileno($reader));
  return unless $reader->sysread(my $chunk, 4194304);

  # Update heartbeats (and stop gracefully if necessary)
  my $time = steady_time;
  while ($chunk =~ /(\d+):(\d)\n/g) {
    next unless my $w = $self->{pool}{$1};
    @$w{qw(healthy time)} = (1, $time) and $self->emit(heartbeat => $1);
    $w->{graceful} ||= $time if $2;
  }
}

1;

=encoding utf8

=head1 NAME

Mojo::Server::Prefork - Pre-forking non-blocking I/O HTTP and WebSocket server

=head1 SYNOPSIS

  use Mojo::Server::Prefork;

  my $prefork = Mojo::Server::Prefork->new(listen => ['http://*:8080']);
  $prefork->unsubscribe('request')->on(request => sub {
    my ($prefork, $tx) = @_;

    # Request
    my $method = $tx->req->method;
    my $path   = $tx->req->url->path;

    # Response
    $tx->res->code(200);
    $tx->res->headers->content_type('text/plain');
    $tx->res->body("$method request for $path!");

    # Resume transaction
    $tx->resume;
  });
  $prefork->run;

=head1 DESCRIPTION

L<Mojo::Server::Prefork> is a full featured, UNIX optimized, pre-forking
non-blocking I/O HTTP and WebSocket server, built around the very well tested
and reliable L<Mojo::Server::Daemon>, with IPv6, TLS, SNI, UNIX domain socket,
Comet (long polling), keep-alive and multiple event loop support. Note that the
server uses signals for process management, so you should avoid modifying signal
handlers in your applications.

For better scalability (epoll, kqueue) and to provide non-blocking name
resolution, SOCKS5 as well as TLS support, the optional modules L<EV> (4.0+),
L<Net::DNS::Native> (0.15+), L<IO::Socket::Socks> (0.64+) and
L<IO::Socket::SSL> (1.84+) will be used automatically if possible. Individual
features can also be disabled with the C<MOJO_NO_NNR>, C<MOJO_NO_SOCKS> and
C<MOJO_NO_TLS> environment variables.

See L<Mojolicious::Guides::Cookbook/"DEPLOYMENT"> for more.

=head1 MANAGER SIGNALS

The L<Mojo::Server::Prefork> manager process can be controlled at runtime with
the following signals.

=head2 INT, TERM

Shut down server immediately.

=head2 QUIT

Shut down server gracefully.

=head2 TTIN

Increase worker pool by one.

=head2 TTOU

Decrease worker pool by one.

=head1 WORKER SIGNALS

L<Mojo::Server::Prefork> worker processes can be controlled at runtime with the
following signals.

=head2 QUIT

Stop worker gracefully.

=head1 EVENTS

L<Mojo::Server::Prefork> inherits all events from L<Mojo::Server::Daemon> and
can emit the following new ones.

=head2 finish

  $prefork->on(finish => sub {
    my ($prefork, $graceful) = @_;
    ...
  });

Emitted when the server shuts down.

  $prefork->on(finish => sub {
    my ($prefork, $graceful) = @_;
    say $graceful ? 'Graceful server shutdown' : 'Server shutdown';
  });

=head2 heartbeat

  $prefork->on(heartbeat => sub {
    my ($prefork, $pid) = @_;
    ...
  });

Emitted when a heartbeat message has been received from a worker.

  $prefork->on(heartbeat => sub {
    my ($prefork, $pid) = @_;
    say "Worker $pid has a heartbeat";
  });

=head2 reap

  $prefork->on(reap => sub {
    my ($prefork, $pid) = @_;
    ...
  });

Emitted when a child process exited.

  $prefork->on(reap => sub {
    my ($prefork, $pid) = @_;
    say "Worker $pid stopped";
  });

=head2 spawn

  $prefork->on(spawn => sub {
    my ($prefork, $pid) = @_;
    ...
  });

Emitted when a worker process is spawned.

  $prefork->on(spawn => sub {
    my ($prefork, $pid) = @_;
    say "Worker $pid started";
  });

=head2 wait

  $prefork->on(wait => sub {
    my $prefork = shift;
    ...
  });

Emitted when the manager starts waiting for new heartbeat messages.

  $prefork->on(wait => sub {
    my $prefork = shift;
    my $workers = $prefork->workers;
    say "Waiting for heartbeat messages from $workers workers";
  });

=head1 ATTRIBUTES

L<Mojo::Server::Prefork> inherits all attributes from L<Mojo::Server::Daemon>
and implements the following new ones.

=head2 accepts

  my $accepts = $prefork->accepts;
  $prefork    = $prefork->accepts(100);

Maximum number of connections a worker is allowed to accept, before stopping
gracefully and then getting replaced with a newly started worker, passed along
to L<Mojo::IOLoop/"max_accepts">, defaults to C<10000>. Setting the value to
C<0> will allow workers to accept new connections indefinitely. Note that up to
half of this value can be subtracted randomly to improve load balancing, and to
make sure that not all workers restart at the same time.

=head2 cleanup

  my $bool = $prefork->cleanup;
  $prefork = $prefork->cleanup($bool);

Delete L</"pid_file"> automatically once it is not needed anymore, defaults to
a true value.

=head2 graceful_timeout

  my $timeout = $prefork->graceful_timeout;
  $prefork    = $prefork->graceful_timeout(15);

Maximum amount of time in seconds stopping a worker gracefully may take before
being forced, defaults to C<120>. Note that this value should usually be a
little larger than the maximum amount of time you expect any one request to
take.

=head2 heartbeat_interval

  my $interval = $prefork->heartbeat_interval;
  $prefork     = $prefork->heartbeat_interval(3);

Heartbeat interval in seconds, defaults to C<5>.

=head2 heartbeat_timeout

  my $timeout = $prefork->heartbeat_timeout;
  $prefork    = $prefork->heartbeat_timeout(2);

Maximum amount of time in seconds before a worker without a heartbeat will be
stopped gracefully, defaults to C<30>. Note that this value should usually be a
little larger than the maximum amount of time you expect any one operation to
block the event loop.

=head2 pid_file

  my $file = $prefork->pid_file;
  $prefork = $prefork->pid_file('/tmp/prefork.pid');

Full path of process id file, defaults to C<prefork.pid> in a temporary
directory.

=head2 spare

  my $spare = $prefork->spare;
  $prefork  = $prefork->spare(4);

Temporarily spawn up to this number of additional workers if there is a need,
defaults to C<2>. This allows for new workers to be started while old ones are
still shutting down gracefully, drastically reducing the performance cost of
worker restarts.

=head2 workers

  my $workers = $prefork->workers;
  $prefork    = $prefork->workers(10);

Number of worker processes, defaults to C<4>. A good rule of thumb is two
worker processes per CPU core for applications that perform mostly non-blocking
operations, blocking operations often require more and benefit from decreasing
concurrency with L<Mojo::Server::Daemon/"clients"> (often as low as C<1>).

=head1 METHODS

L<Mojo::Server::Prefork> inherits all methods from L<Mojo::Server::Daemon> and
implements the following new ones.

=head2 check_pid

  my $pid = $prefork->check_pid;

Get process id for running server from L</"pid_file"> or delete it if server is
not running.

  say 'Server is not running' unless $prefork->check_pid;

=head2 ensure_pid_file

  $prefork->ensure_pid_file($pid);

Ensure L</"pid_file"> exists.

=head2 healthy

  my $healthy = $prefork->healthy;

Number of currently active worker processes with a heartbeat.

=head2 run

  $prefork->run;

Run server and wait for L</"MANAGER SIGNALS">.

=head1 SEE ALSO

L<Mojolicious>, L<Mojolicious::Guides>, L<https://mojolicious.org>.

=cut
