in reply to Hobo with a bit of recursion

Updated: Fully Perl-like behavior for the 1st demonstration.

Greetings Veltro,

Your post presents an interesting use case, for sure. Let me try and hoping that it all works, eventually :)

Q & A

Problem 1: The join is located at a problematic position due to the nature of how hashes work. Sometimes the code takes 6 seconds to execute and sometimes 2 + 6 seconds.

Hashes are not ordered in Perl. The ref key-value went first. In your execute routine, $hobo->join is called. The remedy is to remove the $hobo->join statement out of the routine. It is not needed inside the execute routine when max_workers is given to MCE::Hobo->init.

Problem 2: L2_counter1 => 3 is not incremented.

The tie statement does not deeply share key-values during construction (bug, fix planned for v1.837). The way to shared nested hash/array structures is explicitly via the STORE method.

Problem 3: Why do I need to use a share? The data is incremented independently, so I would think there should be no problems regards synchronicity. However if I don't use the share, nothing gets incremented at all...

The short answer is that workers have unique copies for non-shared variables. Thus, sharing is necessary. MCE::Shared spawns a separate process (a thread on the Windows platform) where the shared data resides. Workers including the main process communicate to the shared-manager process using sockets.

Demo 1: via Perl-like behavior

Shown with mutex in the event multiple workers update the same key. The reason is because ++ involves two trips to the shared-manager process { FETCH and STORE }.

use strict ;
use warnings ;

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

use Data::Dumper ;

sub task1 {
    print "Starting task 1 for $_[0]\n" ;
    sleep 2 ;
    print "Finished task 1 for $_[0]\n" ;
}

sub task2 {
    print "Starting task 2 for $_[0]\n" ;
    sleep 4 ;
    print "Finished task 2 for $_[0]\n" ;
}

sub task3 {
    print "Starting task 3 for $_[0]\n" ;
    sleep 6 ;
    print "Finished task 3 for $_[0]\n" ;
}

MCE::Hobo->init(
    max_workers  => 2,
#     hobo_timeout => 10,
#     posix_exit   => 1,
) ;

my $mutex = MCE::Mutex->new ;

# Construct the shared hash first before assigning key-value pairs.

tie my %test, 'MCE::Shared' ;

# Internally, STORE deeply-shares array/hash references automatically.

%test = (
        L1_counter1 => 1,
        # L1_counter2 => 2,
        # L1_counter3 => 3,
        nested1 => {
                L2_counter1 => 3,
                # L2_counter2 => 2,
                # L2_counter3 => 1,
        },
) ;

sub executeTasks {
    my $in = $_[0] ;

    foreach( sort keys %{ $in } ) {
        my $ref = ref( my $val = $in->{ $_ } ) ;

        if ( $ref && $val->blessed eq 'MCE::Shared::Hash' ) {
            executeTasks( $val ) ;
        } else {
            if ( $val == 1 ) {
                mce_async {
                    task1( $_ ) ;
                    $mutex->enter(sub {
                        ++$in->{ $_ } ;
                    }) ;
                } ;
            } elsif ( $val == 2 ) {
                mce_async {
                    task2( $_ ) ;
                    $mutex->enter(sub {
                        ++$in->{ $_ } ;
                    }) ;
                } ;
            } elsif ( $val == 3 ) {
                mce_async {
                    task3( $_ ) ;
                    $mutex->enter(sub {
                        ++$in->{ $_ } ;
                    }) ;
                } ;
            } ;
        } ;
    } ;
} ;

# Dump shared hash.

print Dumper( tied( %test )->export( { unbless => 1 } ) ) ;

# Begin processing.

executeTasks( \%test ) ;

# Reap any remaining Hobo workers. MCE::Hobo reaps workers
# automatically to not exceed max_workers when given.

MCE::Hobo->waitall ;

# Dump shared hash.

print "\n", Dumper( tied( %test )->export( { unbless => 1 } ) ) ;

[download]

Demo 2: using the OO interface

This eliminates having a mutex at the application level. Btw, the OO interface does not involve TIE for lesser overhead.

use strict ;
use warnings ;

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

use Data::Dumper ;

sub task1 {
    print "Starting task 1 for $_[0]\n" ;
    sleep 2 ;
    print "Finished task 1 for $_[0]\n" ;
}

sub task2 {
    print "Starting task 2 for $_[0]\n" ;
    sleep 4 ;
    print "Finished task 2 for $_[0]\n" ;
}

sub task3 {
    print "Starting task 3 for $_[0]\n" ;
    sleep 6 ;
    print "Finished task 3 for $_[0]\n" ;
}

MCE::Hobo->init(
    max_workers  => 2,
#     hobo_timeout => 10,
#     posix_exit   => 1,
) ;

my $test = MCE::Shared->hash ;

# Must call STORE (not set) for deeply sharing to work.

$test->STORE( L1_counter1 => 1 ) ;
$test->STORE( nested1 => { 'L2_counter1' => 3 } ) ;

sub executeTasks {
    my $in = $_[0] ;

    foreach( sort $in->keys ) {
        my $ref = ref( my $val = $in->get( $_ ) ) ;

        if ( $ref && $val->blessed eq 'MCE::Shared::Hash' ) {
            executeTasks( $val ) ;
        } else {
            if ( $val == 1 ) {
                mce_async {
                    task1( $_ ) ;
                    $in->incr( $_ ) ;
                } ;
            } elsif ( $val == 2 ) {
                mce_async {
                    task2( $_ ) ;
                    $in->incr( $_ ) ;
                } ;
            } elsif ( $val == 3 ) {
                mce_async {
                    task3( $_ ) ;
                    $in->incr( $_ ) ;
                } ;
            } ;
        } ;
    } ;
} ;

# Dump shared hash.

print Dumper( $test->export( { unbless => 1 } ) ) ;

# Begin processing.

executeTasks( $test ) ;

# Reap any remaining Hobo workers. MCE::Hobo reaps workers
# automatically to not exceed max_workers when given.

MCE::Hobo->waitall ;

# Dump shared hash.

print "\n", Dumper( $test->export( { unbless => 1 } ) ) ;

[download]

Output

$VAR1 = {
          'L1_counter1' => 1,
          'nested1' => {
                         'L2_counter1' => 3
                       }
        };
Starting task 1 for L1_counter1
Starting task 3 for L2_counter1
Finished task 1 for L1_counter1
Finished task 3 for L2_counter1

$VAR1 = {
          'nested1' => {
                         'L2_counter1' => 4
                       },
          'L1_counter1' => 2
        };

[download]

Regards, Mario

Replies are listed 'Best First'.
Re^2: Hobo with a bit of recursion
by Veltro (Hermit) on Jun 17, 2018 at 16:23 UTC

    Hello marioroy,

    Thanks for your excellent reply. Besides giving me a couple of very nice examples you also explained sharing to me and the importance of it. I start to see now that I definitively need to do some more studying regards this subject.

    One of your answers (in italic below) leads me to another question regards sharing nested objects

    >> "The tie statement does not deeply share key-values during construction. The way to shared nested hash/array structures is explicitly via the STORE method"

    In case objects are shared that do not have STORE and FETCH methods, and they have nested methods and objects, does this mean that the methods cannot be reached and the objects don't get to be shared?

    Example, Bar object has nested Foo object (inside hash key nestedFoo):

    Foo and Bar definitions:

    Read more... (1355 Bytes)

    Main:

    package main ;
use strict ;
use warnings ;
use MCE::Shared ;
use Data::Dumper ;

my $foo = new Foo ;
my $bar = new Bar( $foo ) ;

# my $barShared = MCE::Shared->share( { module => 'Bar' }, $foo ) ;
# or
# from examples: my $ob = MCE::Shared->share( $blessed_object );
my $barSh = MCE::Shared->share( Bar->new( $foo ) ) ;
print Dumper( $barSh->export ) . "\n" ;
$barSh->task( 'Bar' ) ; # OK
$barSh->{ nestedFoo }->task( 'Foo' ) ; # Not a HASH reference
# Program died here
$barSh->export->{ nestedFoo }->task( 'Foo' ) ; # OK, but not shared?
__END__
$VAR1 = bless( {
                 '_var' => 1,
                 'nestedFoo' => bless( {
                                         '_var' => 1
                                       }, 'Foo' )
               }, 'Bar' );

Starting task Bar for Bar
Not a HASH reference at testHobo3.pl line 60, <__ANONIO__> line 1.
Finished task Bar for Bar

    [download]

    Is there a way to 'get' the nestedFoo in shared context?

    Is there a way to execute task for Foo without export?

    edit: I forgot to mention the nested _var in each of the objects. What I mean with 'shared context' is that each _var become 2 inside of the share after the task methods have been executed.

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      Greetings Veltro,

      Yet another interesting use case :)

      Q & A

      In case objects are shared that do not have STORE and FETCH methods, and they have nested methods and objects, does this mean that the methods cannot be reached and the objects don't get to be shared?

      Is there a way to 'get' the nestedFoo in shared context?

      Is there a way to execute task for Foo without export?

      For shared objects, think of them as having an entry point into the shared-manager process. Important for shared-objects, in the case of MCE::Shared, is to pass arguments instead of dereferencing. Please note that calling a method on a shared-object is executed by the shared-manager where the data resides. For this use case, embed the shared-data object inside the class. That will allow workers to run in parallel and update shared-data accordingly.

      Demo 1: via Perl-like behavior

      Shown with mutex in the event multiple workers update the same key. Like in the prior post, the reason is because ++ involves two trips to the shared-manager process { FETCH and STORE }. I added an export routine to filter out the mutex handle.

      use strict;
use warnings;

package Foo {
    use MCE::Shared ;
    sub new {
        my $class = shift ;
        my $this  = { } ;
        tie my %data, 'MCE::Shared', _var => 1 ;
        $this->{ _SHARED_DATA } = \%data ;
        $this->{ _MUTEX } = MCE::Mutex->new ;
        bless $this, $class ;
    }
    sub task {
        # Long operation task Foo ~ 2 seconds
        my $this = shift ;
        print "Starting task Foo for $_[0]\n" ;
        sleep 2 ;
        $this->{ _MUTEX }->enter( sub {
            ++$this->{ _SHARED_DATA }{ _var } ;
        }) ;
        print "Finished task Foo for $_[0]\n" ;
    }
    sub export {
        my $this  = shift ;
        my %clone = %{ $this } ;
        delete $clone{ _MUTEX } ;
        return \%clone ;
    }
} ;

package Bar {
    use MCE::Shared ;
    use Scalar::Util 'blessed' ;
    sub new {
        my $class = shift ;
        # This is not very realistic code.
        # here it is just used as an
        # example to create an object that
        # contains a nested object
        my $this = { nestedFoo => $_[0] } ;
        tie my %data, 'MCE::Shared', _var => 1 ;
        $this->{ _SHARED_DATA } = \%data ;
        $this->{ _MUTEX } = MCE::Mutex->new ;
        bless $this, $class ;
    }
    sub task {
        my $this = shift ;
        if ( @_ == 2 ) {
            $this->{ $_[0] }->task( $_[1] ) ;
            return ;
        }
        # Long operation task Bar ~ 6 seconds
        print "Starting task Bar for $_[0]\n" ;
        sleep 6 ;
        $this->{ _MUTEX }->enter( sub {
            ++$this->{ _SHARED_DATA }{ _var } ;
        }) ;
        print "Finished task Bar for $_[0]\n" ;
    }
    sub export {
        my $this  = shift ;
        my %clone = %{ $this } ;
        delete $clone{ _MUTEX } ;
        for ( keys %clone ) {
            next unless blessed( $clone{ $_ } ) ;
            next unless $clone{ $_ }->can('export') ;
            $clone{ $_ } = $clone{ $_ }->export ;
        }
        return \%clone ;
    }
} ;

package main ;

use MCE::Hobo ;
use Data::Dumper ;

my $foo = Foo->new ;
my $bar = Bar->new( $foo ) ;

print Dumper( $bar->export ), "\n" ;

mce_async { $bar->task('Bar') } ;
mce_async { $bar->task('nestedFoo', 'Foo') } ;

MCE::Hobo->waitall ;

print "\n", Dumper( $bar->export ), "\n" ;

      [download]

      Demo 2: using the OO interface

      This eliminates the mutex at the application level. Here, the export routine calls export on the shared-data object.

      use strict;
use warnings;

package Foo {
    use MCE::Shared ;
    sub new {
        my $class = shift ;
        my $this  = { } ;
        $this->{ _SHARED_DATA } = MCE::Shared->hash( _var => 1 ) ;
        bless $this, $class ;
    }
    sub task {
        # Long operation task Foo ~ 2 seconds
        my $this = shift ;
        print "Starting task Foo for $_[0]\n" ;
        sleep 2 ;
        $this->{ _SHARED_DATA }->incr('_var') ;
        print "Finished task Foo for $_[0]\n" ;
    }
    sub export {
        my $this  = shift ;
        my %clone = %{ $this } ;
        $clone{ _SHARED_DATA } = $this->{ _SHARED_DATA }->export(
            { unbless => 1 }
        ) ;
        return \%clone ;
    }
} ;

package Bar {
    use MCE::Shared ;
    use Scalar::Util 'blessed' ;
    sub new {
        my $class = shift ;
        # This is not very realistic code.
        # here it is just used as an
        # example to create an object that
        # contains a nested object
        my $this = { nestedFoo => $_[0] } ;
        $this->{ _SHARED_DATA } = MCE::Shared->hash( _var => 1 ) ;
        bless $this, $class ;
    }
    sub task {
        my $this = shift ;
        if ( @_ == 2 ) {
            $this->{ $_[0] }->task( $_[1] ) ;
            return ;
        }
        # Long operation task Bar ~ 6 seconds
        print "Starting task Bar for $_[0]\n" ;
        sleep 6 ;
        $this->{ _SHARED_DATA }->incr('_var') ;
        print "Finished task Bar for $_[0]\n" ;
    }
    sub export {
        my $this  = shift ;
        my %clone = %{ $this } ;
        for ( keys %clone ) {
            next unless blessed( $clone{ $_ } ) ;
            next unless $clone{ $_ }->can('export') ;
            $clone{ $_ } = $clone{ $_ }->export(
                { unbless => 1 }
            ) ;
        }
        return \%clone ;
    }
} ;

package main ;

use MCE::Hobo ;
use Data::Dumper ;

my $foo = Foo->new ;
my $bar = Bar->new( $foo ) ;

print Dumper( $bar->export ), "\n" ;

mce_async { $bar->task('Bar') } ;
mce_async { $bar->task('nestedFoo', 'Foo') } ;

MCE::Hobo->waitall ;

print "\n", Dumper( $bar->export ), "\n" ;

      [download]

      Output

      $VAR1 = {
          '_SHARED_DATA' => {
                              '_var' => 1
                            },
          'nestedFoo' => {
                           '_SHARED_DATA' => {
                                               '_var' => 1
                                             }
                         }
        };

Starting task Bar for Bar
Starting task Foo for Foo
Finished task Foo for Foo
Finished task Bar for Bar

$VAR1 = {
          '_SHARED_DATA' => {
                              '_var' => 2
                            },
          'nestedFoo' => {
                           '_SHARED_DATA' => {
                                               '_var' => 2
                                             }
                         }
        };

      [download]

      Regards, Mario

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