Garbage collection in Perl

perl garbage-collection circular-reference
srikanta picture srikanta · Jun 4, 2010 · Viewed 10.1k times · Source

Unlike Java, Perl uses reference count for garbage collection. I have tried searching some previous questions which speak about C++ RAII and smart pointers and Java GC but have not understood how Perl deals with the circular referencing problem.

Can anyone explain how Perl's garbage collector deals with circular references? Is there any way to reclaim circular referenced memory which are no longer used by the program or does Perl just ignores this problem altogether?

Answer

Max Lybbert picture Max Lybbert · Jun 4, 2010

According to my copy of Programming Perl 3rd ed., on exit Perl 5 does an "expensive mark and sweep" to reclaim circular references. You'll want to avoid circular references as much as possible because otherwise they won't be reclaimed until the program exits.

Perl 5 does offer weak references through the Scalar::Utils module.

Perl 6 will move to a pluggable garbage collected scheme (well, the underlying VM will have multiple garbage collection options and the behavior of those options can have an effect on Perl). That is, you'll be able to choose between various garbage collectors, or implement your own. Want a copying collector? Sure. Want a coloring collector? You got it. Mark/sweep, compacting, etc? Why not?

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