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ChangeLog

NAME

C<Log::Dispatch> - Dispatching multi-source, multi-destination logging


SYNOPSIS

code

=begin code :lang<raku>
use Log::Dispatch;
use Log::Dispatch::Destination;
use Log::Dispatch::Source;

class DBDestination does Log::Ddispatch::Destination {
    method report(Log::Dispatch::Msg:D $message) {
        ... # Implement writing log messages to a database table
    }
}

class MyApp does Log::Dispatch::Source {
    has Log::Dispatch:D $!logger .= new;
    has Str:D $.log-file is required;
    submethod TWEAK {
        $!logger.add: Log::Dispatch::TTY, :max-level(LOG-LEVEL::DEBUG);
        $!logger.add: 'File', file => $!log-file;
        $!logger.add: DBDestination;
    }
    method do-an-action {
        my Bool $success;
        my $diagnostics;

        self.log: :debug, "Trying an action...";

        ... # Do something

        if $success {
            self.log: "All done";
        }
        else {
            self.log: :critical, "Something is wrong! Cause: ", $diagnostics;
        }
    }
}
=end code


DESCRIPTION

This module provide a means to have multiple log destinations withing single application with extra hassle
but with easy support for concurrency.


The model this module is based upon is built around a single dispatcher, which can be considered as a minimalistic
wrapper around a L<C<Supplier>|https://docs.raku.org/type/Supplier>. The dispatcher accepts message objects from sources and dispatches them into
destinations.


A source here is any instance of a class consuming L<C<Log::Dispatch::Source>|Dispatch/Source.md> role.


A destination is an instance of a class consuming L<C<Log::Dispatch::Destination>|Dispatch/Destination.md> role. It represented an endpoint
where messages are to be submitted to.


For example, one may have an application and wants to log its messages into a file and on the console. This is as simple
as adding C<does Log::Dispatch::Source> to the declaration of our application class. And by having something like the
following example anywhere in application code:


=begin code :lang<raku>
my $logger = Log::Dispatch.new;
$logger.add: 'File', :max-level(LOG-LEVEL::DEBUG), $log-file-name;
$logger.add: Log::Dispatch::TTY;
=end code


Note that the application would then log all messages into a log file, but only the essential ones to the console.


It worth to mention that each destination code is by default gets its own thread. For a source it is normally sufficient
just to use `log` method provided by L<C<Log::Dispatch::Source>|Dispatch/Source.md> role.


A I<processor> is an end-point attached to the dispatcher. The module provides two kinds of processors: source and
destination implemented, correspondingly, by L<C<Log::Dispatch::Source>|Dispatch/Source.md> and L<C<Log::Dispatch::Destination>|Dispatch/Destination.md> roles.


C<Log::Dispatch::Processor> role is just an interface requiring C<attach> method to be implemented.


Currently the module only provides two destination end-points: L<C<Log::Dispatch::TTY>|Dispatch/TTY.md> and
L<C<Log::Dispatch::File>|Dispatch/File.md>. Syslog support may be added later.


The multi-destination concept with per-destination maximum log-level support implies that there is no way to optimize
away some possibly unused calls to the method C<log> because any message, no matter what log-level it is assigned with,
must be accepted and emitted into dispatcher's L<C<Supply>|https://docs.raku.org/type/Supply>.


The number and names of log levels are taken from I<syslog> standard exactly for the reason it is the most common
logging standard existing around.


Levels are provided as C<LOG-LEVEL> enum values declared by L<C<Log::Dispatch::Types>|Dispatch/Types.md> module. Here is the list in the
ascending order:


item

This module tries to reduce namespace pollution to the absolute minimum. The only symbol exported is C<LOG-LEVEL>
enumeration type for comparatively simple registration of a destination, as in the above example from the
L<Model|#Model> section.


METHODS

C<multi method add(Log::Dispatch::Processor:D $processor --> Nil)>


Adds an end-point object C<$processor> to the dispatcher.


Note that the C<attach> method of a custom processor is expected to return a L<C<Promise>|https://docs.raku.org/type/Promise> which is to be kept only and
only when the processor is ready. The meaning of being ready would then depend on the end-point type only.


C<multi method add(Log::Dispatch::Processor:U $processor, *%params)>


This method creates an instance of the C<$processor> type using C<%params> as constructor parameters. The resulting
instance is then gets registered with the dispatcher.


C<multi method add(>L<C<Str>|https://docs.raku.org/type/Str>C<:D $processor, *%params)>


This method determines processor type based on the name provided in C<$processor> parameter and then instantiates it
as described for the previous method candidate.


The following rules are used to resolve the type:


See the example in the L<Model|#Model> section above.


Can only be issued once on a dispatcher. Any subsequent call to the method is ignored.


Closes the dispatching supply by invoking method C<done> on the L<C<Supplier>|https://docs.raku.org/type/Supplier>.


The method can be invoked manually when absolutely necessary. But normally is it called inside an C<END> phaser to
ensure that the logging capabilities are available up until the complete stop of the application.


C<dispatch-msg(>L<C<Log::Dispatch::Msg>|Dispatch/Msg.md>C<:D $msg)>


Emits L<C<Log::Dispatch::Msg>|Dispatch/Msg.md> object into the dispatching supply.


AUTHOR

LICENSE

Dispatch

The Raku Knowledge Base


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ChangeLog

CHANGELOG

v0.0.1

Log::Dispatch v0.0.1

Authors

License

Dependencies

Test Dependencies

Provides

Documentation