#!/usr/bin/perl
use strict;
use warnings;
use threads;
use threads::shared;
use Thread::Queue;
use Time::HiRes qw( usleep time );
use IPC::Open3;

my $DEFAULTS = {
  'exit_success'    => 0,   ## success exit.
  'exit_failure'    => 1,   ## failure exit.
  'ret_success'     => 1,   ## success return.
  'ret_failure'     => 0,   ## failure return.

  'random'          => 10,  ## Random amount of time to sleep.
  'max_threads'     => 10,  ## Max # of threads to maintain.
  'test_jobs'       => 20,  ## # of test jobs to run.
};

my @q_JOBS  :shared;            ## shared jobs queue.
my $f_TERM  :shared = 0;        ## main term flag.
my $f_TERM_PRINT  :shared = 0;  ## print term flag.
my $l_PRINT :shared;            ## print lock
my $q_IDLE  :shared;            ## idle queue.
   $q_IDLE = Thread::Queue->new();
my $q_PRINT :shared;            ## print queue.
   $q_PRINT = Thread::Queue->new();

local $SIG{'INT'} = local $SIG{'TERM'} =
sub {
  $q_PRINT->enqueue( 'Signaled TERMINATION' );
  $f_TERM = 1;
  $q_IDLE->insert(0, -1);
};
local $SIG{'KILL'} = sub { threads->exit(); };

sub main {
  ## populate a dummy list of jobs to work.
  ## this could be some server list, or whatever.
  @q_JOBS = map{ 'JOB-'.$_ }(1..$DEFAULTS->{'test_jobs'});

  my $thr_pm = threads->create( \&print_manager )->detach();

  for ( 1..$DEFAULTS->{'max_threads'} ) {
    my $thr_wk = threads->create( \&thread_worker );
  } ## end for max_threads.

  while ( ! $f_TERM ) {
    usleep( 250_000 );
    my $tid = $q_IDLE->dequeue();
    last if ( $tid < 0 );
  }

  $q_PRINT->enqueue( 'Shutdown on main started' );
  shutdown_engine();

} ## end main.

sub shutdown_engine {
  ## Centralized cleanup and shutdown.
  $_->join foreach ( threads->list() );

  while( $q_PRINT->pending() > 0 ) {
    usleep( 250_000 );
  }
  $f_TERM_PRINT = 1;
  exit $DEFAULTS->{'exit_success'};
}

sub get_next_job {
  lock @q_JOBS;
  return shift @q_JOBS;
}

sub thread_worker {
  my $tid = threads->tid();

  while ( ( $#q_JOBS > 0 ) && ( ! $f_TERM ) ) {
    $q_PRINT->enqueue( "Thread $tid is IDLE" );
    $q_IDLE->enqueue($tid, 0);
    my $job = get_next_job();
    do_work( $job, $tid ); ## do whatever work...
  } ## end

  $q_PRINT->enqueue( "Thread $tid is FINISHED" );
  $q_IDLE->insert($tid, -1);

  return $DEFAULTS->{'ret_success'};
} ## end thread_worker.

sub run_external_command {
  ## serves as a place for extensive
  ## external command where output
  ## and secondary processing may
  ## take place.
  my ( $job, $tid ) = @_;
  $q_PRINT->enqueue( "Thread $tid is running exteral job $job" );
  local( *w_IN, *w_OUT, *w_ERR );
  my $pid = open3( \*w_IN, \*w_OUT, \*w_ERR, '/bin/sleep', int( rand($DEFAULTS->{'random'} ) ) );
  waitpid( $pid, 0 );
  return $DEFAULTS->{'ret_success'};
}
sub do_work {
  ## do_work could be a wrapper to whatever type
  ## of work needs to be accomplished. For now,
  ## I will just sleep.
  my ($job, $tid) = @_;
  $q_IDLE->enqueue($tid, 1);
  $q_PRINT->enqueue( "Thread $tid is WORKING [$job]" );
  ## pretend it takes some time before running the
  ## external command -- i.e. mix shit up a bit.
  sleep( int( rand( 5 ) ) );
  run_external_command( $job, $tid );
  $q_PRINT->enqueue( "Thread $tid COMPLETED [$job]" );
  return $DEFAULTS->{'ret_success'};
} ## end do_work.

sub timestamp {
  return localtime time;
} ## end timestamp.

sub print_manager {
  lock $l_PRINT;
  while ( ! $f_TERM_PRINT ) {
    usleep(100_000);
    print STDOUT  '[' . timestamp() . ']: '
                  . $q_PRINT->dequeue() . "\n";
  }
  threads->exit();
} ## end print_manager.

main();

exit $DEFAULTS->{'exit_success'};
__END__