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

use Fcntl ':flock';
use File::Spec::Functions qw(catfile tmpdir);
use IO::Poll 'POLLIN';
use List::Util 'shuffle';
use POSIX 'WNOHANG';
use Scalar::Util 'weaken';
use Time::HiRes ();

has accepts         => 1000;
has accept_interval => 0.025;
has [qw(graceful_timeout heartbeat_timeout)] => 20;
has heartbeat_interval => 5;
has lock_file          => sub { catfile tmpdir, 'prefork.lock' };
has lock_timeout       => 0.5;
has multi_accept       => 50;
has pid_file           => sub { catfile tmpdir, 'prefork.pid' };
has workers            => 4;

sub DESTROY {
  my $self = shift;

  # Worker
  return unless $self->{finished};

  # Manager
  if (my $file = $self->{lock_file}) { unlink $file if -w $file }
  if (my $file = $self->pid_file)    { unlink $file if -w $file }
}

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 if -w $file;
  return undef;
}

sub run {
  my $self = shift;

  # No Windows support
  say 'Preforking not available for Windows.' and exit 0 if $^O eq 'MSWin32';

  # Prepare lock file and event loop
  $self->{lock_file} = $self->lock_file . ".$$";
  my $loop = $self->ioloop->max_accepts($self->accepts);
  $loop->$_($self->$_) for qw(accept_interval multi_accept);

  # Pipe for worker communication
  pipe($self->{reader}, $self->{writer}) or die "Can't create pipe: $!";
  $self->{poll} = IO::Poll->new;
  $self->{poll}->mask($self->{reader}, POLLIN);

  # Clean manager environment
  local $SIG{INT} = local $SIG{TERM} = sub { $self->_term };
  local $SIG{CHLD} = sub {
    while ((my $pid = waitpid -1, WNOHANG) > 0) { $self->_reap($pid) }
  };
  local $SIG{QUIT} = sub { $self->_term(1) };
  local $SIG{TTIN} = sub { $self->workers($self->workers + 1) };
  local $SIG{TTOU} = sub {
    $self->workers($self->workers - 1) if $self->workers > 0;
    return unless $self->workers;
    $self->{pool}{shuffle keys %{$self->{pool}}}{graceful} ||= time;
  };

  # Preload application and start accepting connections
  $self->start->app->log->info("Manager $$ started.");
  $self->{running} = 1;
  $self->_manage while $self->{running};
}

sub _heartbeat {
  my $self = shift;

  # Poll for heartbeats
  my $poll = $self->{poll};
  $poll->poll(1);
  return unless $poll->handles(POLLIN);
  return unless $self->{reader}->sysread(my $chunk, 4194304);

  # Update heartbeats
  $self->{pool}{$1} and $self->emit(heartbeat => $1)->{pool}{$1}{time} = time
    while $chunk =~ /(\d+)\n/g;
}

sub _manage {
  my $self = shift;

  # Spawn more workers and check PID file
  if (!$self->{finished}) {
    $self->_spawn while keys %{$self->{pool}} < $self->workers;
    $self->_pid_file;
  }

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

  # Manage workers
  $self->emit('wait')->_heartbeat;
  my $log = $self->app->log;
  while (my ($pid, $w) = each %{$self->{pool}}) {

    # No heartbeat (graceful stop)
    my $interval = $self->heartbeat_interval;
    my $timeout  = $self->heartbeat_timeout;
    if (!$w->{graceful} && ($w->{time} + $interval + $timeout <= time)) {
      $log->info("Worker $pid has no heartbeat, restarting.");
      $w->{graceful} = time;
    }

    # Graceful stop with timeout
    $w->{graceful} ||= time if $self->{graceful};
    if ($w->{graceful}) {
      $log->debug("Trying to stop worker $pid gracefully.");
      kill 'QUIT', $pid;
      $w->{force} = 1 if $w->{graceful} + $self->graceful_timeout <= time;
    }

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

sub _pid_file {
  my $self = shift;

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

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

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

  # CLean up dead worker
  $self->app->log->debug("Worker $pid stopped.")
    if delete $self->emit(reap => $pid)->{pool}{$pid};
}

sub _spawn {
  my $self = shift;

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

  # Prepare lock file
  my $file = $self->{lock_file};
  die qq{Can't open lock file "$file": $!} unless open my $handle, '>', $file;

  # Change user/group
  my $loop = $self->setuidgid->ioloop;

  # Accept mutex
  $loop->lock(
    sub {

      # Blocking ("ualarm" can't be imported on Windows)
      my $l;
      if ($_[1]) {
        eval {
          local $SIG{ALRM} = sub { die "alarm\n" };
          my $old = Time::HiRes::ualarm $self->lock_timeout * 1000000;
          $l = flock $handle, LOCK_EX;
          Time::HiRes::ualarm $old;
        };
        if ($@) { $l = $@ eq "alarm\n" ? 0 : die($@) }
      }

      # Non blocking
      else { $l = flock $handle, LOCK_EX | LOCK_NB }

      return $l;
    }
  );
  $loop->unlock(sub { flock $handle, LOCK_UN });

  # Heartbeat messages (stop sending during graceful stop)
  weaken $self;
  $loop->recurring(
    $self->heartbeat_interval => sub {
      return unless shift->max_connections;
      $self->{writer}->syswrite("$$\n") or exit 0;
    }
  );

  # Clean worker environment
  $SIG{$_} = 'DEFAULT' for qw(INT TERM CHLD TTIN TTOU);
  $SIG{QUIT} = sub { $loop->max_connections(0) };
  delete $self->{$_} for qw(poll reader);

  # Start event loop
  $self->app->log->debug("Worker $$ started.");
  $loop->start;
  exit 0;
}

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

1;

=head1 NAME

Mojo::Server::Prefork - Preforking 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');
  $prefork->on(request => sub {
    my ($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, preforking
non-blocking I/O HTTP and WebSocket server, built around the very well tested
and reliable L<Mojo::Server::Daemon>, with C<IPv6>, C<TLS>, C<Comet> (long
polling) and multiple event loop support. Note that the server uses signals
for process management, so you should avoid modifying signal handlers in your
applications.

Optional modules L<EV> (4.0+), L<IO::Socket::IP> (0.16+) and
L<IO::Socket::SSL> (1.75+) are supported transparently through
L<Mojo::IOLoop>, and used if installed. Individual features can also be
disabled with the C<MOJO_NO_IPV6> and C<MOJO_NO_TLS> environment variables.

See L<Mojolicious::Guides::Cookbook> for more.

=head1 SIGNALS

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

=head2 Manager

=over 2

=item INT, TERM

Shutdown server immediately.

=item QUIT

Shutdown server gracefully.

=item TTIN

Increase worker pool by one.

=item TTOU

Decrease worker pool by one.

=back

=head2 Worker

=over 2

=item INT, TERM

Stop worker immediately.

=item QUIT

Stop worker gracefully.

=back

=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 dies.

  $prefork->on(reap => sub {
    my ($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 accept_interval

  my $interval = $prefork->accept_interval;
  $prefork     = $prefork->accept_interval(0.5);

Interval in seconds for trying to reacquire the accept mutex and connection
management, defaults to C<0.025>. Note that changing this value can affect
performance and idle CPU usage.

=head2 accepts

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

Maximum number of connections a worker is allowed to accept before stopping
gracefully, defaults to C<1000>. 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 that worker processes
will stop sending heartbeat messages once the limit has been reached.

=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<20>.

=head2 heartbeat_interval

  my $interval = $prefork->heartbeat_intrval;
  $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<20>.

=head2 lock_file

  my $file = $prefork->lock_file;
  $prefork = $prefork->lock_file('/tmp/prefork.lock');

Full path of accept mutex lock file prefix, to which the process id will be
appended, defaults to a random temporary path.

=head2 lock_timeout

  my $timeout = $prefork->lock_timeout;
  $prefork    = $prefork->lock_timeout(1);

Maximum amount of time in seconds a worker may block when waiting for the
accept mutex, defaults to C<0.5>.

=head2 multi_accept

  my $multi = $prefork->multi_accept;
  $prefork  = $prefork->multi_accept(100);

Number of connections to accept at once, defaults to C<50>.

=head2 pid_file

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

Full path of process id file, defaults to a random temporary path.

=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.

=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 C<pid_file> or delete it if server is
not running.

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

=head2 run

  $prefork->run;

Run server.

=head1 SEE ALSO

L<Mojolicious>, L<Mojolicious::Guides>, L<http://mojolicio.us>.

=cut