Subroutine Attributes
A subroutine declaration or definition may have a list
of attributes associated with it. If such an attribute list is
present, it is broken up at whitespace or colon boundaries and treated
as though a use attributes
had been seen. See the
use attributes
pragma in Glossary for internal details. There
are three standard attributes for subroutines:
locked
, method
, and
lvalue
.
The locked and method Attributes
# Only one thread is allowed into this function. sub afunc : locked { … } # Only one thread is allowed into this function on a given object. sub afunc : locked method { … }
Setting the locked
attribute is meaningful
only when the subroutine or method is intended to be called by
multiple threads simultaneously. When set on a nonmethod subroutine,
Perl ensures that a lock is acquired on the subroutine itself before
that subroutine is entered. When set on a method subroutine (that
is, one also marked with the method
attribute),
Perl ensures that any invocation of it implicitly locks its first
argument (the object) before execution.
Semantics of this lock are the same as using the
lock
operator on the subroutine as the first
statement in that routine. See Chapter
17, for more on locking.
The method
attribute can be used by
itself:
sub afunc : method { … }
Currently this has only the effect of marking the subroutine
so as not to trigger the "Ambiguous call resolved as
CORE::%s
" warning. (We may make it mean more
someday.)
The attribute system is user-extensible, ...
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