Ubuntu Manpage: Object::Remote - Call methods on objects in other processes or on other hosts

name
synopsis
description
components
methods
environment
known issues
support
author
contributors
sponsors
copyright
license

Provided by: libobject-remote-perl_0.004004-1_all

NAME

       Object::Remote - Call methods on objects in other processes or on other hosts

SYNOPSIS

       Creating a connection:

         use Object::Remote;

         my $conn = Object::Remote->connect('myserver'); # invokes ssh

       Calling a subroutine:

         my $capture = IPC::System::Simple->can::on($conn, 'capture');

         warn $capture->('uptime');

       Using an object:

         my $eval = Eval::WithLexicals->new::on($conn);

         $eval->eval(q{my $x = `uptime`});

         warn $eval->eval(q{$x});

       Importantly: 'myserver' only requires perl 5.8+ - no non-core modules need to be installed on the far
       side, Object::Remote takes care of it for you!

DESCRIPTION

       Object::Remote allows you to create an object in another process - usually one running on another machine
       you can connect to via ssh, although there are other connection mechanisms available.

       The idea here is that in many cases one wants to be able to run a piece of code on another machine, or
       perhaps many other machines - but without having to install anything on the far side.

COMPONENTS

   Object::Remote
       The "main" API, which provides the "connect" method to create a connection to a remote process/host,
       "new::on" to create an object on a connection, and "can::on" to retrieve a subref over a connection.

   Object::Remote::Connection
       The object representing a connection, which provides the "remote_object" in Object::Remote::Connection
       and "remote_sub" in Object::Remote::Connection methods that are used by "new::on" and "can::on" to return
       proxies for objects and subroutines on the far side.

   Object::Remote::Future
       Code for dealing with asynchronous operations, which provides the "start::method" in
       Object::Remote::Future syntax for calling a possibly asynchronous method without blocking, and
       "await_future" in Object::Remote::Future and "await_all" in Object::Remote::Future to block until an
       asynchronous call completes or fails.

METHODS

   connect
         my $conn = Object::Remote->connect('-'); # fork()ed connection

         my $conn = Object::Remote->connect('myserver'); # connection over ssh

         my $conn = Object::Remote->connect('user@myserver'); # connection over ssh

         my $conn = Object::Remote->connect('root@'); # connection over sudo

   new::on
         my $eval = Eval::WithLexicals->new::on($conn);

         my $eval = Eval::WithLexicals->new::on('myserver'); # implicit connect

         my $obj = Some::Class->new::on($conn, %args); # with constructor arguments

   can::on
         my $hostname = Sys::Hostname->can::on($conn, 'hostname');

         my $hostname = Sys::Hostname->can::on('myserver', 'hostname');

ENVIRONMENT

       OBJECT_REMOTE_PERL_BIN
           When starting a new Perl interpreter the contents of this environment variable will be used as the
           path to the executable. If the variable is not set the path is 'perl'

       OBJECT_REMOTE_LOG_LEVEL
           Setting this environment variable will enable logging and send all log messages at the specified
           level or higher to STDERR. Valid level names are: trace debug verbose info warn error fatal

       OBJECT_REMOTE_LOG_FORMAT
           The format of the logging output is configurable. By setting this environment variable the format can
           be controlled via printf style position variables. See Object::Remote::Logging::Logger.

       OBJECT_REMOTE_LOG_FORWARDING
           Forward log events from remote connections to the local Perl interpreter. Set to 1 to enable this
           feature which is disabled by default. See Object::Remote::Logging.

       OBJECT_REMOTE_LOG_SELECTIONS
           Space separated list of class names to display logs for if logging output is enabled. Default value
           is "Object::Remote::Logging" which selects all logs generated by Object::Remote.  See
           Object::Remote::Logging.

KNOWN ISSUES

Large data structures
Object::Remote communication is encapsalated with JSON and values passed to remote objects will be
serialized with it. When sending large data structures or data structures with a lot of deep
complexity (hashes in arrays in hashes in arrays) the processor time and memory requirements for
serialization and deserialization can be either painful or unworkable. During times of serialization
the local or remote nodes will be blocked potentially causing all remote interpreters to block as
well under worse case conditions.

To help deal with this issue it is possible to configure resource ulimits for a Perl interpreter that
is executed by Object::Remote. See "Object::Remote::Role::Connector::PerlInterpreter" for details on
the perl_command attribute.

User can starve run loop of execution opportunities
The Object::Remote run loop is responsible for performing I/O and managing timers in a cooperative
multitasing way but it can only do these tasks when the user has given control to Object::Remote.
There are times when Object::Remote must wait for the user to return control to the run loop and
during these times no I/O can be performed and no timers can be executed.

As an end user of Object::Remote if you depend on connection timeouts, the watch dog or timely
results from remote objects then be sure to hand control back to Object::Remote as soon as you can.

Run loop favors certain filehandles/connections
High levels of load can starve timers of execution opportunities
These are issues that only become a problem at large scales. The end result of these two issues is
quite similar: some remote objects may block while the local run loop is either busy servicing a
different connection or is not executing because control has not yet been returned to it. For the
same reasons timers may not get an opportunity to execute in a timely way.

Internally Object::Remote uses timers managed by the run loop for control tasks. Under high load the
timers can be preempted by servicing I/O on the filehandles and execution can be severely delayed.
This can lead to connection watchdogs not being updated or connection timeouts taking longer than
configured.

Deadlocks
Deadlocks can happen quite easily because of flaws in programs that use Object::Remote or
Object::Remote itself so the "Object::Remote::WatchDog" is available. When used the run loop will
periodically update the watch dog object on the remote Perl interpreter. If the watch dog goes longer
than the configured interval with out being updated then it will terminate the Perl process. The
watch dog will terminate the process even if a deadlock condition has occurred.

Log forwarding at scale can starve timers of execution opportunities
Currently log forwarding can be problematic at large scales. When there is a large amount of log
events the load produced by log forwarding can be high enough that it starves the timers and the
remote object watch dogs (if in use) don't get updated in timely way causing them to erroneously
terminate the Perl process. If the watch dog is not in use then connection timeouts can be delayed
but will execute when load settles down enough.

Because of the load related issues Object::Remote disables log forwarding by default. See
"Object::Remote::Logging" for information on log forwarding.

SUPPORT

       IRC: #web-simple on irc.perl.org

AUTHOR

       mst - Matt S. Trout (cpan:MSTROUT) <mst@shadowcat.co.uk>

CONTRIBUTORS

       bfwg - Colin Newell (cpan:NEWELLC) <colin.newell@gmail.com>

       phaylon - Robert Sedlacek (cpan:PHAYLON) <r.sedlacek@shadowcat.co.uk>

       triddle - Tyler Riddle (cpan:TRIDDLE) <t.riddle@shadowcat.co.uk>

COPYRIGHT

       Copyright (c) 2012 the Object::Remote "AUTHOR", "CONTRIBUTORS" and "SPONSORS" as listed above.

LICENSE

       This library is free software and may be distributed under the same terms as perl itself.