devel::refcount(3pm) [debian man page]

Devel::Refcount(3pm)					User Contributed Perl Documentation				      Devel::Refcount(3pm)

NAME

       "Devel::Refcount" - obtain the REFCNT value of a referent

SYNOPSIS

	use Devel::Refcount qw( refcount );

	my $anon = [];

	print "Anon ARRAY $anon has " . refcount($anon) . " reference
";

	my $otherref = $anon;

	print "Anon ARRAY $anon now has " . refcount($anon) . " references
";

DESCRIPTION

       This module provides a single function which obtains the reference count of the object being pointed to by the passed reference value.

FUNCTIONS

   $count = refcount($ref)
       Returns the reference count of the object being pointed to by $ref.

COMPARISON WITH SvREFCNT
       This function differs from "Devel::Peek::SvREFCNT" in that SvREFCNT() gives the reference count of the SV object itself that it is passed,
       whereas refcount() gives the count of the object being pointed to. This allows it to give the count of any referent (i.e. ARRAY, HASH,
       CODE, GLOB and Regexp types) as well.

       Consider the following example program:

	use Devel::Peek qw( SvREFCNT );
	use Devel::Refcount qw( refcount );

	sub printcount
	{
	   my $name = shift;

	   printf "%30s has SvREFCNT=%d, refcount=%d
",
	      $name, SvREFCNT($_[0]), refcount($_[0]);
	}

	my $var = [];

	printcount 'Initially, $var', $var;

	my $othervar = $var;

	printcount 'Before CODE ref, $var', $var;
	printcount '$othervar', $othervar;

	my $code = sub { undef $var };

	printcount 'After CODE ref, $var', $var;
	printcount '$othervar', $othervar;

       This produces the output

		       Initially, $var has SvREFCNT=1, refcount=1
		 Before CODE ref, $var has SvREFCNT=1, refcount=2
			     $othervar has SvREFCNT=1, refcount=2
		  After CODE ref, $var has SvREFCNT=2, refcount=2
			     $othervar has SvREFCNT=1, refcount=2

       Here, we see that SvREFCNT() counts the number of references to the SV object passed in as the scalar value - the $var or $othervar
       respectively, whereas refcount() counts the number of reference values that point to the referent object - the anonymous ARRAY in this
       case.

       Before the CODE reference is constructed, both $var and $othervar have SvREFCNT() of 1, as they exist only in the current lexical pad. The
       anonymous ARRAY has a refcount() of 2, because both $var and $othervar store a reference to it.

       After the CODE reference is constructed, the $var variable now has an SvREFCNT() of 2, because it also appears in the lexical pad for the
       new anonymous CODE block.

PURE-PERL FALLBACK
       An XS implementation of this function is provided, and is used by default. If the XS library cannot be loaded, a fallback implementation in
       pure perl using the "B" module is used instead. This will behave identically, but is much slower.

	       Rate   pp   xs
	pp 225985/s   -- -66%
	xs 669570/s 196%   --

SEE ALSO

       o   Test::Refcount - assert reference counts on objects

AUTHOR

       Paul Evans <leonerd@leonerd.org.uk>

perl v5.14.2							    2011-11-15						      Devel::Refcount(3pm)

Check Out this Related Man Page

REFCOUNT(9)						   BSD Kernel Developer's Manual					       REFCOUNT(9)

NAME

     refcount, refcount_init, refcount_acquire, refcount_release -- manage a simple reference counter

SYNOPSIS

     #include <sys/param.h>
     #include <sys/refcount.h>

     void
     refcount_init(volatile u_int *count, u_int value);

     void
     refcount_acquire(volatile u_int *count);

     int
     refcount_release(volatile u_int *count);

DESCRIPTION

     The refcount functions provide an API to manage a simple reference counter.  The caller provides the storage for the counter in an unsigned
     integer.  A pointer to this integer is passed via count.  Usually the counter is used to manage the lifetime of an object and is stored as a
     member of the object.

     The refcount_init() function is used to set the initial value of the counter to value.  It is normally used when creating a reference-counted
     object.

     The refcount_acquire() function is used to acquire a new reference.  The caller is responsible for ensuring that it holds a valid reference
     while obtaining a new reference.  For example, if an object is stored on a list and the list holds a reference on the object, then holding a
     lock that protects the list provides sufficient protection for acquiring a new reference.

     The refcount_release() function is used to release an existing reference.	The function returns a non-zero value if the reference being
     released was the last reference; otherwise, it returns zero.

     Note that these routines do not provide any inter-CPU synchronization, data protection, or memory ordering guarantees except for managing the
     counter.  The caller is responsible for any additional synchronization needed by consumers of any containing objects.  In addition, the call-
     er is also responsible for managing the life cycle of any containing objects including explicitly releasing any resources when the last ref-
     erence is released.

RETURN VALUES

     The refcount_release function returns non-zero when releasing the last reference and zero when releasing any other reference.

HISTORY

     These functions were introduced in FreeBSD 6.0.

BSD
								 January 20, 2009							       BSD

Linux and UNIX Man Pages

devel::refcount(3pm) [debian man page]

Check Out this Related Man Page