The code responsible for executing callbacks (as in the $h->{Callbacks} feature) saves a copy of *_{SCALAR} (that is, the scalar slot of the *_typeglob), replaces it with a reference to a temporary scalar (containing the name of the method being called), invokes the callback, and then restores the old *_{SCALAR}. This works like manually localizing (and then unlocalizing) $_.
However, before restoring the old $_, the code would increment its reference count "to compensate for the ref count decrement that will happen when we exit the scope". As far as I can tell, this never made any sense: $_ is a global variable and we never decrement its reference count. All this did is increment the reference count of $_ for no reason. This was usually harmless: $_ is a global variable anyway. But if $_ is localized (explicitly or by for (...)) when a callback runs, the local value of $_ would leak.
Fix the leak by removing the spurious SvREFCNT_inc.
The code responsible for executing callbacks (as in the $h->{Callbacks} feature) saves a copy of
*_{SCALAR}(that is, the scalar slot of the*_typeglob), replaces it with a reference to a temporary scalar (containing the name of the method being called), invokes the callback, and then restores the old*_{SCALAR}. This works like manually localizing (and then unlocalizing)$_.However, before restoring the old
$_, the code would increment its reference count "to compensate for the ref count decrement that will happen when we exit the scope". As far as I can tell, this never made any sense:$_is a global variable and we never decrement its reference count. All this did is increment the reference count of$_for no reason. This was usually harmless:$_is a global variable anyway. But if$_is localized (explicitly or byfor (...)) when a callback runs, the local value of$_would leak.Fix the leak by removing the spurious SvREFCNT_inc.
Fixes RT#144526.