NAME

MCE::Hobo - A threads-like parallelization module

VERSION

This document describes MCE::Hobo version 1.886

SYNOPSIS

use MCE::Hobo;

MCE::Hobo->init(
    max_workers => 'auto',   # default undef, unlimited

    # Specify a percentage. MCE::Hobo 1.874+.
    max_workers => '25%',    # 4 on HW with 16 lcores
    max_workers => '50%',    # 8 on HW with 16 lcores

    hobo_timeout => 20,      # default undef, no timeout
    posix_exit => 1,         # default undef, CORE::exit
    void_context => 1,       # default undef

    on_start => sub {
        my ( $pid, $ident ) = @_;
        ...
    },
    on_finish => sub {
        my ( $pid, $exit, $ident, $signal, $error, @ret ) = @_;
        ...
    }
);

MCE::Hobo->create( sub { print "Hello from hobo\n" } )->join();

sub parallel {
    my ($arg1) = @_;
    print "Hello again, $arg1\n" if defined($arg1);
    print "Hello again, $_\n"; # same thing
}

MCE::Hobo->create( \&parallel, $_ ) for 1 .. 3;

my @hobos    = MCE::Hobo->list();
my @pids     = MCE::Hobo->list_pids();
my @running  = MCE::Hobo->list_running();
my @joinable = MCE::Hobo->list_joinable();
my @count    = MCE::Hobo->pending();

# Joining is orderly, e.g. hobo1 is joined first, hobo2, hobo3.
$_->join() for @hobos;   # (or)
$_->join() for @joinable;

# Joining occurs immediately as hobo processes complete execution.
1 while MCE::Hobo->wait_one();

my $hobo = mce_async { foreach (@files) { ... } };

$hobo->join();

if ( my $err = $hobo->error() ) {
    warn "Hobo error: $err\n";
}

# Get a hobo's object
$hobo = MCE::Hobo->self();

# Get a hobo's ID
$pid = MCE::Hobo->pid();  # $$
$pid = $hobo->pid();
$pid = MCE::Hobo->tid();  # tid is an alias for pid
$pid = $hobo->tid();

# Test hobo objects
if ( $hobo1 == $hobo2 ) {
    ...
}

# Give other workers a chance to run
MCE::Hobo->yield();
MCE::Hobo->yield(0.05);

# Return context, wantarray aware
my ($value1, $value2) = $hobo->join();
my $value = $hobo->join();

# Check hobo's state
if ( $hobo->is_running() ) {
    sleep 1;
}
if ( $hobo->is_joinable() ) {
    $hobo->join();
}

# Send a signal to a hobo
$hobo->kill('SIGUSR1');

# Exit a hobo
MCE::Hobo->exit(0);
MCE::Hobo->exit(0, @ret);  # MCE::Hobo 1.827+

DESCRIPTION

A hobo is a migratory worker inside the machine that carries the asynchronous gene. Hobo processes are equipped with threads-like capability for running code asynchronously. Unlike threads, each hobo is a unique process to the underlying OS. The IPC is managed by MCE::Shared, which runs on all the major platforms including Cygwin and Strawberry Perl.

An exception was made on the Windows platform to spawn threads versus children in MCE::Hobo 1.807 through 1.816. For consistency, the 1.817 release reverts back to spawning children on all supported platforms.

MCE::Hobo may be used as a standalone or together with MCE including running alongside threads.

use MCE::Hobo;
use MCE::Shared;

# synopsis: head -20 file.txt | perl script.pl

my $ifh = MCE::Shared->handle( "<", \*STDIN  );  # shared
my $ofh = MCE::Shared->handle( ">", \*STDOUT );
my $ary = MCE::Shared->array();

sub parallel_task {
    my ( $id ) = @_;
    while ( <$ifh> ) {
        printf {$ofh} "[ %4d ] %s", $., $_;
      # $ary->[ $. - 1 ] = "[ ID $id ] read line $.\n" );  # dereferencing
        $ary->set( $. - 1, "[ ID $id ] read line $.\n" );  # faster via OO
    }
}

my $hobo1 = MCE::Hobo->new( "parallel_task", 1 );
my $hobo2 = MCE::Hobo->new( \&parallel_task, 2 );
my $hobo3 = MCE::Hobo->new( sub { parallel_task(3) } );

$_->join for MCE::Hobo->list();  # ditto: MCE::Hobo->wait_all();

# search array (total one round-trip via IPC)
my @vals = $ary->vals( "val =~ / ID 2 /" );

print {*STDERR} join("", @vals);

API DOCUMENTATION

$hobo = MCE::Hobo->create( FUNCTION, ARGS )

$hobo = MCE::Hobo->new( FUNCTION, ARGS )

This will create a new hobo process that will begin execution with function as the entry point, and optionally ARGS for list of parameters. It will return the corresponding MCE::Hobo object, or undef if hobo creation failed.

FUNCTION may either be the name of a function, an anonymous subroutine, or a code ref.

my $hobo = MCE::Hobo->create( "func_name", ... );
    # or
my $hobo = MCE::Hobo->create( sub { ... }, ... );
    # or
my $hobo = MCE::Hobo->create( \&func, ... );

$hobo = MCE::Hobo->create( { options }, FUNCTION, ARGS )

$hobo = MCE::Hobo->create( IDENT, FUNCTION, ARGS )

Options, excluding ident, may be specified globally via the init function. Otherwise, ident, hobo_timeout, posix_exit, and void_context may be set uniquely.

The ident option, available since 1.827, is used by callback functions on_start and on_finish for identifying the started and finished hobo process respectively.

my $hobo1 = MCE::Hobo->create( { posix_exit => 1 }, sub {
    ...
} );

$hobo1->join;

my $hobo2 = MCE::Hobo->create( { hobo_timeout => 3 }, sub {
    sleep 1 for ( 1 .. 9 );
} );

$hobo2->join;

if ( $hobo2->error() eq "Hobo timed out\n" ) {
    ...
}

The new() method is an alias for create().

mce_async { BLOCK } ARGS;

mce_async { BLOCK };

mce_async runs the block asynchronously similarly to MCE::Hobo->create(). It returns the hobo object, or undef if hobo creation failed.

my $hobo = mce_async { foreach (@files) { ... } };

$hobo->join();

if ( my $err = $hobo->error() ) {
    warn("Hobo error: $err\n");
}

$hobo->join()

This will wait for the corresponding hobo process to complete its execution. In non-voided context, join() will return the value(s) of the entry point function.

The context (void, scalar or list) for the return value(s) for join is determined at the time of joining and mostly wantarray aware.

my $hobo1 = MCE::Hobo->create( sub {
    my @res = qw(foo bar baz);
    return (@res);
});

my @res1 = $hobo1->join();  # ( foo, bar, baz )
my $res1 = $hobo1->join();  #   baz

my $hobo2 = MCE::Hobo->create( sub {
    return 'foo';
});

my @res2 = $hobo2->join();  # ( foo )
my $res2 = $hobo2->join();  #   foo

$hobo1->equal( $hobo2 )

Tests if two hobo objects are the same hobo or not. Hobo comparison is based on process IDs. This is overloaded to the more natural forms.

if ( $hobo1 == $hobo2 ) {
    print("Hobo objects are the same\n");
}
# or
if ( $hobo1 != $hobo2 ) {
    print("Hobo objects differ\n");
}

$hobo->error()

Hobo processes are executed in an eval context. This method will return undef if the hobo terminates normally. Otherwise, it returns the value of $@ associated with the hobo's execution status in its eval context.

$hobo->exit()

This sends 'SIGQUIT' to the hobo process, notifying the hobo to exit. It returns the hobo object to allow for method chaining. It is important to join later if not immediately to not leave a zombie or defunct process.

$hobo->exit()->join();
...

$hobo->join();  # later

MCE::Hobo->exit( 0 )

MCE::Hobo->exit( 0, @ret )

A hobo can exit at any time by calling MCE::Hobo->exit(). Otherwise, the behavior is the same as exit(status) when called from the main process. Current since 1.827, the hobo process may optionally return data, to be sent via IPC.

MCE::Hobo->finish()

This class method is called automatically by END, but may be called explicitly. An error is emitted via croak if there are active hobo processes not yet joined.

MCE::Hobo->create( 'task1', $_ ) for 1 .. 4;
$_->join for MCE::Hobo->list();

MCE::Hobo->create( 'task2', $_ ) for 1 .. 4;
$_->join for MCE::Hobo->list();

MCE::Hobo->create( 'task3', $_ ) for 1 .. 4;
$_->join for MCE::Hobo->list();

MCE::Hobo->finish();

MCE::Hobo->init( options )

The init function accepts a list of MCE::Hobo options.

MCE::Hobo->init(
    max_workers => 'auto',   # default undef, unlimited

    # Specify a percentage. MCE::Hobo 1.874+.
    max_workers => '25%',    # 4 on HW with 16 lcores
    max_workers => '50%',    # 8 on HW with 16 lcores

    hobo_timeout => 20,      # default undef, no timeout
    posix_exit => 1,         # default undef, CORE::exit
    void_context => 1,       # default undef

    on_start => sub {
        my ( $pid, $ident ) = @_;
        ...
    },
    on_finish => sub {
        my ( $pid, $exit, $ident, $signal, $error, @ret ) = @_;
        ...
    }
);

# Identification given as an option or the 1st argument.
# Current API available since 1.827.

for my $key ( 'aa' .. 'zz' ) {
    MCE::Hobo->create( { ident => $key }, sub { ... } );
    MCE::Hobo->create( $key, sub { ... } );
}

MCE::Hobo->wait_all;

Set max_workers if you want to limit the number of workers by waiting automatically for an available slot. Specify a percentage or auto to obtain the number of logical cores via MCE::Util::get_ncpu().

Set hobo_timeout, in number of seconds, if you want the hobo process to terminate after some time. The default is 0 for no timeout.

Set posix_exit to avoid all END and destructor processing. Constructing MCE::Hobo inside a thread implies 1 or if present CGI, FCGI, Coro, Curses, Gearman::Util, Gearman::XS, LWP::UserAgent, Mojo::IOLoop, STFL, Tk, Wx, or Win32::GUI.

Set void_context to create the hobo process in void context for the return value. Otherwise, the return context is wantarray-aware for join() and result() and determined when retrieving the data.

The callback options on_start and on_finish are called in the parent process after starting the worker and later when terminated. The arguments for the subroutines were inspired by Parallel::ForkManager.

The parameters for on_start are the following:

- pid of the hobo process
- identification (ident option or 1st arg to create)

The parameters for on_finish are the following:

- pid of the hobo process
- program exit code
- identification (ident option or 1st arg to create)
- exit signal id
- error message from eval inside MCE::Hobo
- returned data

$hobo->is_running()

Returns true if a hobo is still running.

$hobo->is_joinable()

Returns true if the hobo has finished running and not yet joined.

$hobo->kill( 'SIG...' )

Sends the specified signal to the hobo. Returns the hobo object to allow for method chaining. As with exit, it is important to join eventually if not immediately to not leave a zombie or defunct process.

$hobo->kill('SIG...')->join();

The following is a parallel demonstration comparing MCE::Shared against Redis and Redis::Fast on a Fedora 23 VM. Joining begins after all workers have been notified to quit.

use Time::HiRes qw(time);

use Redis;
use Redis::Fast;

use MCE::Hobo;
use MCE::Shared;

my $redis = Redis->new();
my $rfast = Redis::Fast->new();
my $array = MCE::Shared->array();

sub parallel_redis {
    my ($_redis) = @_;
    my ($count, $quit, $len) = (0, 0);

    # instead, use a flag to exit loop
    $SIG{'QUIT'} = sub { $quit = 1 };

    while () {
        $len = $_redis->rpush('list', $count++);
        last if $quit;
    }

    $count;
}

sub parallel_array {
    my ($count, $quit, $len) = (0, 0);

    # do not exit from inside handler
    $SIG{'QUIT'} = sub { $quit = 1 };

    while () {
        $len = $array->push($count++);
        last if $quit;
    }

    $count;
}

sub benchmark_this {
    my ($desc, $num_procs, $timeout, $code, @args) = @_;
    my ($start, $total) = (time(), 0);

    MCE::Hobo->new($code, @args) for 1..$num_procs;
    sleep $timeout;

    # joining is not immediate; ok
    $_->kill('QUIT') for MCE::Hobo->list();

    # joining later; ok
    $total += $_->join() for MCE::Hobo->list();

    printf "$desc <> duration: %0.03f secs, count: $total\n",
        time() - $start;

    sleep 0.2;
}

benchmark_this('Redis      ', 8, 5.0, \&parallel_redis, $redis);
benchmark_this('Redis::Fast', 8, 5.0, \&parallel_redis, $rfast);
benchmark_this('MCE::Shared', 8, 5.0, \&parallel_array);

MCE::Hobo->list()

Returns a list of all hobo objects not yet joined.

@hobos = MCE::Hobo->list();

MCE::Hobo->list_pids()

Returns a list of all hobo pids not yet joined (available since 1.849).

@pids = MCE::Hobo->list_pids();

$SIG{INT} = $SIG{HUP} = $SIG{TERM} = sub {
    # Signal workers and the shared manager all at once
    CORE::kill('KILL', MCE::Hobo->list_pids(), MCE::Shared->pid());
    exec('reset');
};

MCE::Hobo->list_running()

Returns a list of all hobo objects that are still running.

@hobos = MCE::Hobo->list_running();

MCE::Hobo->list_joinable()

Returns a list of all hobo objects that have completed running. Thus, ready to be joined without blocking.

@hobos = MCE::Hobo->list_joinable();

MCE::Hobo->max_workers([ N ])

Getter and setter for max_workers. Specify a number or 'auto' to acquire the total number of cores via MCE::Util::get_ncpu. Specify a false value to set back to no limit.

API available since 1.835.

MCE::Hobo->pending()

Returns a count of all hobo objects not yet joined.

$count = MCE::Hobo->pending();

$hobo->result()

Returns the result obtained by join, wait_one, or wait_all. If the process has not yet exited, waits for the corresponding hobo to complete its execution.

use MCE::Hobo;
use Time::HiRes qw(sleep);

sub task {
    my ($id) = @_;
    sleep $id * 0.333;
    return $id;
}

MCE::Hobo->create('task', $_) for ( reverse 1 .. 3 );

# 1 while MCE::Hobo->wait_one();

while ( my $hobo = MCE::Hobo->wait_one() ) {
    my $err = $hobo->error() || 'no error';
    my $res = $hobo->result();
    my $pid = $hobo->pid();

    print "[$pid] $err : $res\n";
}

Like join described above, the context (void, scalar or list) for the return value(s) is determined at the time result is called and mostly wantarray aware.

my $hobo1 = MCE::Hobo->create( sub {
    my @res = qw(foo bar baz);
    return (@res);
});

my @res1 = $hobo1->result();  # ( foo, bar, baz )
my $res1 = $hobo1->result();  #   baz

my $hobo2 = MCE::Hobo->create( sub {
    return 'foo';
});

my @res2 = $hobo2->result();  # ( foo )
my $res2 = $hobo2->result();  #   foo

MCE::Hobo->self()

Class method that allows a hobo to obtain it's own MCE::Hobo object.

$hobo->pid()

$hobo->tid()

Returns the ID of the hobo.

pid: $$  process id
tid: $$  alias for pid

MCE::Hobo->pid()

MCE::Hobo->tid()

Class methods that allows a hobo to obtain its own ID.

pid: $$  process id
tid: $$  alias for pid

MCE::Hobo->wait_one()

MCE::Hobo->waitone()

MCE::Hobo->wait_all()

MCE::Hobo->waitall()

Meaningful for the manager process only, waits for one or all hobo processes to complete execution. Afterwards, returns the corresponding hobo objects. If a hobo doesn't exist, returns the undef value or an empty list for wait_one and wait_all respectively.

The waitone and waitall methods are aliases since 1.827 for backwards compatibility.

use MCE::Hobo;
use Time::HiRes qw(sleep);

sub task {
    my $id = shift;
    sleep $id * 0.333;
    return $id;
}

MCE::Hobo->create('task', $_) for ( reverse 1 .. 3 );

# join, traditional use case
$_->join() for MCE::Hobo->list();

# wait_one, simplistic use case
1 while MCE::Hobo->wait_one();

# wait_one
while ( my $hobo = MCE::Hobo->wait_one() ) {
    my $err = $hobo->error() || 'no error';
    my $res = $hobo->result();
    my $pid = $hobo->pid();

    print "[$pid] $err : $res\n";
}

# wait_all
my @hobos = MCE::Hobo->wait_all();

for ( @hobos ) {
    my $err = $_->error() || 'no error';
    my $res = $_->result();
    my $pid = $_->pid();

    print "[$pid] $err : $res\n";
}

MCE::Hobo->yield( [ floating_seconds ] )

Prior API till 1.826.

Let this hobo yield CPU time to other workers. By default, the class method calls sleep(0.008) on UNIX and sleep(0.015) on Windows including Cygwin.

MCE::Hobo->yield();
MCE::Hobo->yield(0.05);

# total run time: 0.25 seconds, sleep occuring in parallel

MCE::Hobo->create( sub { MCE::Hobo->yield(0.25) } ) for 1 .. 4;
MCE::Hobo->wait_all();

Current API available since 1.827.

Give other workers a chance to run, optionally for given time. Yield behaves similarly to MCE's interval option. It throttles workers from running too fast. A demonstration is provided in the next section for fetching URLs in parallel.

The default floating_seconds is 0.008 and 0.015 on UNIX and Windows, respectively. Pass 0 if simply wanting to give other workers a chance to run.

# total run time: 1.00 second

MCE::Hobo->create( sub { MCE::Hobo->yield(0.25) } ) for 1 .. 4;
MCE::Hobo->wait_all();

THREADS-like DETACH CAPABILITY

Threads-like detach capability was added starting with the 1.867 release.

A threads example is shown first followed by the MCE::Hobo example. All one needs to do is set the CHLD signal handler to IGNORE. Unfortunately, this works on UNIX platforms only. The hobo process restores the CHLD handler to default, so is able to deeply spin workers and reap if desired.

use threads;

for ( 1 .. 8 ) {
    async {
        # do something
    }->detach;
}

use MCE::Hobo;

# Have the OS reap workers automatically when exiting.
# The on_finish option is ignored if specified (no-op).
# Ensure not inside a thread on UNIX platforms.

$SIG{CHLD} = 'IGNORE';

for ( 1 .. 8 ) {
    mce_async {
        # do something
    };
}

# Optionally, wait for any remaining workers before leaving.
# This is necessary if workers are consuming shared objects,
# constructed via MCE::Shared. 

MCE::Hobo->wait_all;

The following is another way and works on Windows. Here, the on_finish handler works as usual.

use MCE::Hobo;

MCE::Hobo->init(
    on_finish = sub {
        ...
    },
);

for ( 1 .. 8 ) {
    $_->join for MCE::Hobo->list_joinable;
    mce_async {
        # do something
    };
}

MCE::Hobo->wait_all;

PARALLEL::FORKMANAGER-like DEMONSTRATION

MCE::Hobo behaves similarly to threads for the most part. It also provides Parallel::ForkManager-like capabilities. The Parallel::ForkManager example is shown first followed by a version using MCE::Hobo.

Parallel::ForkManager

use strict;
use warnings;

use Parallel::ForkManager;
use Time::HiRes 'time';

my $start = time;

my $pm = Parallel::ForkManager->new(10);
$pm->set_waitpid_blocking_sleep(0);

$pm->run_on_finish( sub {
    my ($pid, $exit_code, $ident, $exit_signal, $core_dumped, $resp) = @_;
    print "child $pid completed: $ident => ", $resp->[0], "\n";
});

DATA_LOOP:
foreach my $data ( 1..2000 ) {
    # forks and returns the pid for the child
    my $pid = $pm->start($data) and next DATA_LOOP;
    my $ret = [ $data * 2 ];

    $pm->finish(0, $ret);
}

$pm->wait_all_children;

printf STDERR "duration: %0.03f seconds\n", time - $start;

MCE::Hobo

use strict;
use warnings;

use MCE::Hobo 1.843;
use Time::HiRes 'time';

my $start = time;

MCE::Hobo->init(
    max_workers => 10,
    on_finish   => sub {
        my ($pid, $exit_code, $ident, $exit_signal, $error, $resp) = @_;
        print "child $pid completed: $ident => ", $resp->[0], "\n";
    }
);

foreach my $data ( 1..2000 ) {
    MCE::Hobo->create( $data, sub {
        [ $data * 2 ];
    });
}

MCE::Hobo->wait_all;

printf STDERR "duration: %0.03f seconds\n", time - $start;

Time to spin 2,000 workers and obtain results (in seconds).

Results were obtained on a Macbook Pro (2.6 GHz ~ 3.6 GHz with Turbo Boost). Parallel::ForkManager 2.02 uses Moo. Therefore, I ran again with Moo loaded at the top of the script.

MCE::Hobo uses MCE::Shared to retrieve data during reaping.
MCE::Child uses MCE::Channel, no shared-manager.

         Version  Cygwin   Windows  Linux   macOS  FreeBSD

MCE::Child 1.843  19.099s  17.091s  0.965s  1.534s  1.229s
 MCE::Hobo 1.843  20.514s  19.594s  1.246s  1.629s  1.613s
     P::FM 1.20   19.703s  19.235s  0.875s  1.445s  1.346s

MCE::Child 1.843  20.426s  18.417s  1.116s  1.632s  1.338s  Moo loaded
 MCE::Hobo 1.843  21.809s  20.810s  1.407s  1.759s  1.722s  Moo loaded
     P::FM 2.02   21.668s  25.927s  1.882s  2.612s  2.483s  Moo used

Set posix_exit to avoid all END and destructor processing.

This is helpful for reducing overhead when workers exit. Ditto if using a Perl module not parallel safe. The option is ignored on Windows $^O eq 'MSWin32'.

MCE::Child->init( posix_exit => 1, ... );
 MCE::Hobo->init( posix_exit => 1, ... );

         Version  Cygwin   Windows  Linux   macOS  FreeBSD

MCE::Child 1.843  19.815s  ignored  0.824s  1.284s  1.245s  Moo loaded
 MCE::Hobo 1.843  21.029s  ignored  0.953s  1.335s  1.439s  Moo loaded

PARALLEL HTTP GET DEMONSTRATION USING ANYEVENT

This demonstration constructs two queues, two handles, starts the shared-manager process if needed, and spawns four workers. For this demonstration, am chunking 64 URLs per job. In reality, one may run with 200 workers and chunk 300 URLs on a 24-way box.

# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# perl demo.pl              -- all output
# perl demo.pl  >/dev/null  -- mngr/hobo output
# perl demo.pl 2>/dev/null  -- show results only
#
# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

use strict;
use warnings;

use AnyEvent;
use AnyEvent::HTTP;
use Time::HiRes qw( time );

use MCE::Hobo;
use MCE::Shared;

# Construct two queues, input and return.

my $que = MCE::Shared->queue();
my $ret = MCE::Shared->queue();

# Construct shared handles for serializing output from many workers
# writing simultaneously. This prevents garbled output.

mce_open my $OUT, ">>", \*STDOUT or die "open error: $!";
mce_open my $ERR, ">>", \*STDERR or die "open error: $!";

# Spawn workers early for minimum memory consumption.

MCE::Hobo->create({ posix_exit => 1 }, 'task', $_) for 1 .. 4;

# Obtain or generate input data for workers to process.

my ( $count, @urls ) = ( 0 );

push @urls, map { "http://127.0.0.$_/"   } 1..254;
push @urls, map { "http://192.168.0.$_/" } 1..254; # 508 URLs total

while ( @urls ) {
    my @chunk = splice(@urls, 0, 64);
    $que->enqueue( { ID => ++$count, INPUT => \@chunk } );
}

# So that workers leave the loop after consuming the queue.

$que->end();

# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Loop for the manager process. The manager may do other work if
# need be and periodically check $ret->pending() not shown here.
#
# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

my $start = time;

printf {$ERR} "Mngr - entering loop\n";

while ( $count ) {
    my ( $result, $failed ) = $ret->dequeue( 2 );

    # Remove ID from result, so not treated as a URL item.

    printf {$ERR} "Mngr - received job %s\n", delete $result->{ID};

    # Display the URL and the size captured.

    foreach my $url ( keys %{ $result } ) {
        printf {$OUT} "%s: %d\n", $url, length($result->{$url})
            if $result->{$url};  # url has content
    }

    # Display URLs could not reach.

    if ( @{ $failed } ) {
        foreach my $url ( @{ $failed } ) {
            print {$OUT} "Failed: $url\n";
        }
    }

    # Decrement the count.

    $count--;
}

MCE::Hobo->wait_all();

printf {$ERR} "Mngr - exiting loop\n\n";
printf {$ERR} "Duration: %0.3f seconds\n\n", time - $start;

exit;

# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Hobo processes enqueue two items ( $result and $failed ) per each
# job for the manager process. Likewise, the manager process dequeues
# two items above. Optionally, hobo processes may include the ID in
# the result.
#
# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

sub task {
    my ( $id ) = @_;
    printf {$ERR} "Hobo $id entering loop\n";

    while ( my $job = $que->dequeue() ) {
        my ( $result, $failed ) = ( { ID => $job->{ID} }, [ ] );

        # Walk URLs, provide a hash and array refs for data.

        printf {$ERR} "Hobo $id running  job $job->{ID}\n";
        walk( $job, $result, $failed );

        # Send results to the manager process.

        $ret->enqueue( $result, $failed );
    }

    printf {$ERR} "Hobo $id exiting loop\n";
}

sub walk {
    my ( $job, $result, $failed ) = @_;

    # Yielding is critical when running an event loop in parallel.
    # Not doing so means that the app may reach contention points
    # with the firewall and likely impose unnecessary hardship at
    # the OS level. The idea here is not to have multiple workers
    # initiate HTTP requests to a batch of URLs at the same time.
    # Yielding in 1.827+ behaves similarly like scatter to have
    # the hobo process run solo for a fraction of time.

    MCE::Hobo->yield( 0.03 );   # MCE::Hobo 1.827+

    my $cv = AnyEvent->condvar();

    # Populate the hash ref for the URLs it could reach.
    # Do not mix AnyEvent timeout with hobo timeout.
    # Therefore, choose event timeout when available.

    foreach my $url ( @{ $job->{INPUT} } ) {
        $cv->begin();
        http_get $url, timeout => 2, sub {
            my ( $data, $headers ) = @_;
            $result->{$url} = $data;
            $cv->end();
        };
    }

    $cv->recv();

    # Populate the array ref for URLs it could not reach.

    foreach my $url ( @{ $job->{INPUT} } ) {
        push @{ $failed }, $url unless (exists $result->{ $url });
    }

    return;
}

__END__

$ perl demo.pl

Hobo 1 entering loop
Hobo 2 entering loop
Hobo 3 entering loop
Mngr - entering loop
Hobo 2 running  job 2
Hobo 3 running  job 3
Hobo 1 running  job 1
Hobo 4 entering loop
Hobo 4 running  job 4
Hobo 2 running  job 5
Mngr - received job 2
Hobo 3 running  job 6
Mngr - received job 3
Hobo 1 running  job 7
Mngr - received job 1
Hobo 4 running  job 8
Mngr - received job 4
http://192.168.0.1/: 3729
Hobo 2 exiting loop
Mngr - received job 5
Hobo 3 exiting loop
Mngr - received job 6
Hobo 1 exiting loop
Mngr - received job 7
Hobo 4 exiting loop
Mngr - received job 8
Mngr - exiting loop

Duration: 4.131 seconds

CROSS-PLATFORM TEMPLATE FOR BINARY EXECUTABLE

Making an executable is possible with the PAR::Packer module. On the Windows platform, threads, threads::shared, and exiting via threads are necessary for the binary to exit successfully.

# https://metacpan.org/pod/PAR::Packer
# https://metacpan.org/pod/pp
#
#   pp -o demo.exe demo.pl
#   ./demo.exe

use strict;
use warnings;

use if $^O eq "MSWin32", "threads";
use if $^O eq "MSWin32", "threads::shared";

# Include minimum dependencies for MCE::Hobo.
# Add other modules required by your application here.

use Storable ();
use Time::HiRes ();

# use IO::FDPass ();  # optional: for condvar, handle, queue
# use Sereal ();      # optional: for faster serialization

use MCE::Hobo;
use MCE::Shared;

# For PAR to work on the Windows platform, one must include manually
# any shared modules used by the application.

# use MCE::Shared::Array;    # if using MCE::Shared->array
# use MCE::Shared::Cache;    # if using MCE::Shared->cache
# use MCE::Shared::Condvar;  # if using MCE::Shared->condvar
# use MCE::Shared::Handle;   # if using MCE::Shared->handle, mce_open
# use MCE::Shared::Hash;     # if using MCE::Shared->hash
# use MCE::Shared::Minidb;   # if using MCE::Shared->minidb
# use MCE::Shared::Ordhash;  # if using MCE::Shared->ordhash
# use MCE::Shared::Queue;    # if using MCE::Shared->queue
# use MCE::Shared::Scalar;   # if using MCE::Shared->scalar

# Et cetera. Only load modules needed for your application.

use MCE::Shared::Sequence;   # if using MCE::Shared->sequence

my $seq = MCE::Shared->sequence( 1, 9 );

sub task {
    my ( $id ) = @_;
    while ( defined ( my $num = $seq->next() ) ) {
        print "$id: $num\n";
        sleep 1;
    }
}

sub main {
    MCE::Hobo->new( \&task, $_ ) for 1 .. 3;
    MCE::Hobo->wait_all();
}

# Main must run inside a thread on the Windows platform or workers
# will fail duing exiting, causing the exe to crash. The reason is
# that PAR or a dependency isn't multi-process safe.

( $^O eq "MSWin32" ) ? threads->create(\&main)->join() : main();

threads->exit(0) if $INC{"threads.pm"};

CREDITS

The inspiration for MCE::Hobo comes from wanting threads-like behavior for processes. Both can run side-by-side including safe-use by MCE workers. Likewise, the documentation resembles threads.

The inspiration for wait_all and wait_one comes from the Parallel::WorkUnit module.

SEE ALSO

• forks

• forks::BerkeleyDB

• MCE::Child

• Parallel::ForkManager

• Parallel::Loops

• Parallel::Prefork

• Parallel::WorkUnit

• Proc::Fork

• Thread::Tie

• threads

INDEX

MCE, MCE::Channel, MCE::Shared

AUTHOR

Mario E. Roy, <marioeroy AT gmail DOT com>

cpanm MCE::Shared

perl -MCPAN -e shell
install MCE::Shared