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Method::Protected - add "is protected" trait to methods


use Method::Protected;

my @words = "/usr/share/dict/words".IO.lines;

class Frobnicate {
    has %!hash;
    method pick() is protected { %!hash{@words.pick}++ }
    method hash() is protected { %!hash.clone          }

# Set up 2 threads massively updating a single hash
my $frobnicator = Frobnicate.new;
start { loop { $frobnicator.pick }
start { loop { $frobnicator.pick }

# Start reporter
until $frobnicator.hash.elems == @words.elems {
    say $frobnicator.hash.elems;
    sleep .1;


Method::Protected provides an is protected trait to methods in a class. If applied to a method, all calls to that method will be protected by a Lock, making sure that any other method call to this method (or any other method protected by the trait) from another thread, will block until the call is finished.

Functionally this is similar to what the OO::Monitor does, except that with this module this logic is only applied to methods that actuall have the is protected trait applied.


When the trait is applied on a method, the class of the method id checked whether it already has a $!LOCK attribute. If not, then that attribute is added, and the associated accessor method LOCK is also added. Then the method will be wrapped with code that will protect the execution of the original body of the method.


If the method being protected has an is raw or is rw trait set, then the protected version will also have that set. However, this is usually used to return a container, which can potentially cause a race-condition outside of the protected method because the container may contain logic that would execute code in a non-threadsafe manner (e.g. in the autovivification of keys in a hash).

So only is is raw or is rw on protected methods if you really know what you're doing. Generally spoken: don't do that! If you think you need to do this, first find another way to structure your code, e.g. by using hyper.


Elizabeth Mattijsen liz@raku.rocks

Source can be located at: https://github.com/lizmat/Method-Protected . Comments and Pull Requests are welcome.

If you like this module, or what I’m doing more generally, committing to a small sponsorship would mean a great deal to me!


Copyright 2024 Elizabeth Mattijsen

This library is free software; you can redistribute it and/or modify it under the Artistic License 2.0.