[perl5.git] / cv.h

/*    cv.h
 *
 *    Copyright (C) 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1999,
 *    2000, 2001, 2002, 2003, 2004, 2005, 2006, by Larry Wall and others
 *
 *    You may distribute under the terms of either the GNU General Public
 *    License or the Artistic License, as specified in the README file.
 *
 */

/* This structure must the beginning of XPVFM in sv.h  */

struct xpvcv {
    NV		xnv_nv;		/* numeric value, if any */
    STRLEN	xpv_cur;	/* length of xp_pv as a C string */
    STRLEN	xpv_len;	/* allocated size */
    union {
	IV	xivu_iv;	/* integer value or pv offset */
	UV	xivu_uv;
	void *	xivu_p1;
    }		xiv_u;
    MAGIC*	xmg_magic;	/* magic for scalar array */
    HV*		xmg_stash;	/* class package */

    HV *	xcv_stash;
    union {
	OP *	xcv_start;
	ANY	xcv_xsubany;
    }		xcv_start_u;
    union {
	OP *	xcv_root;
	void	(*xcv_xsub) (pTHX_ CV*);
    }		xcv_root_u;
    GV *	xcv_gv;
    char *	xcv_file;
    long	xcv_depth;	/* >= 2 indicates recursive call */
    PADLIST *	xcv_padlist;
    CV *	xcv_outside;
    cv_flags_t	xcv_flags;
    U32		xcv_outside_seq; /* the COP sequence (at the point of our
				  * compilation) in the lexically enclosing
				  * sub */
};

/*
=head1 Handy Values

=for apidoc AmU||Nullcv
Null CV pointer.

=head1 CV Manipulation Functions

=for apidoc Am|HV*|CvSTASH|CV* cv
Returns the stash of the CV.

=cut
*/

#define Nullcv Null(CV*)

#define CvSTASH(sv)	((XPVCV*)SvANY(sv))->xcv_stash
#define CvSTART(sv)	((XPVCV*)SvANY(sv))->xcv_start_u.xcv_start
#define CvROOT(sv)	((XPVCV*)SvANY(sv))->xcv_root_u.xcv_root
#define CvXSUB(sv)	((XPVCV*)SvANY(sv))->xcv_root_u.xcv_xsub
#define CvXSUBANY(sv)	((XPVCV*)SvANY(sv))->xcv_start_u.xcv_xsubany
#define CvGV(sv)	((XPVCV*)SvANY(sv))->xcv_gv
#define CvFILE(sv)	((XPVCV*)SvANY(sv))->xcv_file
#ifdef USE_ITHREADS
#  define CvFILE_set_from_cop(sv, cop)	(CvFILE(sv) = savepv(CopFILE(cop)))
#else
#  define CvFILE_set_from_cop(sv, cop)	(CvFILE(sv) = CopFILE(cop))
#endif
#define CvFILEGV(sv)	(gv_fetchfile(CvFILE(sv)))
#define CvDEPTH(sv)	((XPVCV*)SvANY(sv))->xcv_depth
#define CvPADLIST(sv)	((XPVCV*)SvANY(sv))->xcv_padlist
#define CvOUTSIDE(sv)	((XPVCV*)SvANY(sv))->xcv_outside
#define CvFLAGS(sv)	((XPVCV*)SvANY(sv))->xcv_flags
#define CvOUTSIDE_SEQ(sv) ((XPVCV*)SvANY(sv))->xcv_outside_seq

#define CVf_METHOD	0x0001	/* CV is explicitly marked as a method */
#define CVf_LOCKED	0x0002	/* CV locks itself or first arg on entry */
#define CVf_LVALUE	0x0004  /* CV return value can be used as lvalue */
#define CVf_ASSERTION   0x0008  /* CV called only when asserting */

#define CVf_WEAKOUTSIDE	0x0010  /* CvOUTSIDE isn't ref counted */
#define CVf_CLONE	0x0020	/* anon CV uses external lexicals */
#define CVf_CLONED	0x0040	/* a clone of one of those */
#define CVf_ANON	0x0080	/* CvGV() can't be trusted */
#define CVf_UNIQUE	0x0100	/* sub is only called once (eg PL_main_cv,
				 * require, eval). Not to be confused
				 * with the GVf_UNIQUE flag associated
				 * with the :unique attribute */
#define CVf_NODEBUG	0x0200	/* no DB::sub indirection for this CV
				   (esp. useful for special XSUBs) */
#define CVf_CONST	0x0400  /* inlinable sub */
#define CVf_OLDSTYLE	0x0800
#define CVf_ISXSUB	0x1000	/* CV is an XSUB, not pure perl.  */

/* This symbol for optimised communication between toke.c and op.c: */
#define CVf_BUILTIN_ATTRS	(CVf_METHOD|CVf_LOCKED|CVf_LVALUE|CVf_ASSERTION)

#define CvCLONE(cv)		(CvFLAGS(cv) & CVf_CLONE)
#define CvCLONE_on(cv)		(CvFLAGS(cv) |= CVf_CLONE)
#define CvCLONE_off(cv)		(CvFLAGS(cv) &= ~CVf_CLONE)

#define CvCLONED(cv)		(CvFLAGS(cv) & CVf_CLONED)
#define CvCLONED_on(cv)		(CvFLAGS(cv) |= CVf_CLONED)
#define CvCLONED_off(cv)	(CvFLAGS(cv) &= ~CVf_CLONED)

#define CvANON(cv)		(CvFLAGS(cv) & CVf_ANON)
#define CvANON_on(cv)		(CvFLAGS(cv) |= CVf_ANON)
#define CvANON_off(cv)		(CvFLAGS(cv) &= ~CVf_ANON)

#ifdef PERL_XSUB_OLDSTYLE
#define CvOLDSTYLE(cv)		(CvFLAGS(cv) & CVf_OLDSTYLE)
#define CvOLDSTYLE_on(cv)	(CvFLAGS(cv) |= CVf_OLDSTYLE)
#define CvOLDSTYLE_off(cv)	(CvFLAGS(cv) &= ~CVf_OLDSTYLE)
#endif

#define CvUNIQUE(cv)		(CvFLAGS(cv) & CVf_UNIQUE)
#define CvUNIQUE_on(cv)		(CvFLAGS(cv) |= CVf_UNIQUE)
#define CvUNIQUE_off(cv)	(CvFLAGS(cv) &= ~CVf_UNIQUE)

#define CvNODEBUG(cv)		(CvFLAGS(cv) & CVf_NODEBUG)
#define CvNODEBUG_on(cv)	(CvFLAGS(cv) |= CVf_NODEBUG)
#define CvNODEBUG_off(cv)	(CvFLAGS(cv) &= ~CVf_NODEBUG)

#define CvMETHOD(cv)		(CvFLAGS(cv) & CVf_METHOD)
#define CvMETHOD_on(cv)		(CvFLAGS(cv) |= CVf_METHOD)
#define CvMETHOD_off(cv)	(CvFLAGS(cv) &= ~CVf_METHOD)

#define CvLOCKED(cv)		(CvFLAGS(cv) & CVf_LOCKED)
#define CvLOCKED_on(cv)		(CvFLAGS(cv) |= CVf_LOCKED)
#define CvLOCKED_off(cv)	(CvFLAGS(cv) &= ~CVf_LOCKED)

#define CvLVALUE(cv)		(CvFLAGS(cv) & CVf_LVALUE)
#define CvLVALUE_on(cv)		(CvFLAGS(cv) |= CVf_LVALUE)
#define CvLVALUE_off(cv)	(CvFLAGS(cv) &= ~CVf_LVALUE)

#define CvASSERTION(cv)		(CvFLAGS(cv) & CVf_ASSERTION)
#define CvASSERTION_on(cv)	(CvFLAGS(cv) |= CVf_ASSERTION)
#define CvASSERTION_off(cv)	(CvFLAGS(cv) &= ~CVf_ASSERTION)

#define CvEVAL(cv)		(CvUNIQUE(cv) && !SvFAKE(cv))
#define CvEVAL_on(cv)		(CvUNIQUE_on(cv),SvFAKE_off(cv))
#define CvEVAL_off(cv)		CvUNIQUE_off(cv)

/* BEGIN|CHECK|INIT|END */
#define CvSPECIAL(cv)		(CvUNIQUE(cv) && SvFAKE(cv))
#define CvSPECIAL_on(cv)	(CvUNIQUE_on(cv),SvFAKE_on(cv))
#define CvSPECIAL_off(cv)	(CvUNIQUE_off(cv),SvFAKE_off(cv))

#define CvCONST(cv)		(CvFLAGS(cv) & CVf_CONST)
#define CvCONST_on(cv)		(CvFLAGS(cv) |= CVf_CONST)
#define CvCONST_off(cv)		(CvFLAGS(cv) &= ~CVf_CONST)

#define CvWEAKOUTSIDE(cv)	(CvFLAGS(cv) & CVf_WEAKOUTSIDE)
#define CvWEAKOUTSIDE_on(cv)	(CvFLAGS(cv) |= CVf_WEAKOUTSIDE)
#define CvWEAKOUTSIDE_off(cv)	(CvFLAGS(cv) &= ~CVf_WEAKOUTSIDE)

#define CvISXSUB(cv)		(CvFLAGS(cv) & CVf_ISXSUB)
#define CvISXSUB_on(cv)		(CvFLAGS(cv) |= CVf_ISXSUB)
#define CvISXSUB_off(cv)	(CvFLAGS(cv) &= ~CVf_ISXSUB)

/*
=head1 CV reference counts and CvOUTSIDE

=for apidoc m|bool|CvWEAKOUTSIDE|CV *cv

Each CV has a pointer, C<CvOUTSIDE()>, to its lexically enclosing
CV (if any). Because pointers to anonymous sub prototypes are
stored in C<&> pad slots, it is a possible to get a circular reference,
with the parent pointing to the child and vice-versa. To avoid the
ensuing memory leak, we do not increment the reference count of the CV
pointed to by C<CvOUTSIDE> in the I<one specific instance> that the parent
has a C<&> pad slot pointing back to us. In this case, we set the
C<CvWEAKOUTSIDE> flag in the child. This allows us to determine under what
circumstances we should decrement the refcount of the parent when freeing
the child.

There is a further complication with non-closure anonymous subs (i.e. those
that do not refer to any lexicals outside that sub). In this case, the
anonymous prototype is shared rather than being cloned. This has the
consequence that the parent may be freed while there are still active
children, eg

    BEGIN { $a = sub { eval '$x' } }

In this case, the BEGIN is freed immediately after execution since there
are no active references to it: the anon sub prototype has
C<CvWEAKOUTSIDE> set since it's not a closure, and $a points to the same
CV, so it doesn't contribute to BEGIN's refcount either.  When $a is
executed, the C<eval '$x'> causes the chain of C<CvOUTSIDE>s to be followed,
and the freed BEGIN is accessed.

To avoid this, whenever a CV and its associated pad is freed, any
C<&> entries in the pad are explicitly removed from the pad, and if the
refcount of the pointed-to anon sub is still positive, then that
child's C<CvOUTSIDE> is set to point to its grandparent. This will only
occur in the single specific case of a non-closure anon prototype
having one or more active references (such as C<$a> above).

One other thing to consider is that a CV may be merely undefined
rather than freed, eg C<undef &foo>. In this case, its refcount may
not have reached zero, but we still delete its pad and its C<CvROOT> etc.
Since various children may still have their C<CvOUTSIDE> pointing at this
undefined CV, we keep its own C<CvOUTSIDE> for the time being, so that
the chain of lexical scopes is unbroken. For example, the following
should print 123:

    my $x = 123;
    sub tmp { sub { eval '$x' } }
    my $a = tmp();
    undef &tmp;
    print  $a->();

=cut
*/

/*
 * Local variables:
 * c-indentation-style: bsd
 * c-basic-offset: 4
 * indent-tabs-mode: t
 * End:
 *
 * ex: set ts=8 sts=4 sw=4 noet:
 */
Commit	Line	Data
a0d0e21e	1	/* cv.h
79072805	2	*
4bb101f2	3	* Copyright (C) 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1999,
bf53b3a5	4	* 2000, 2001, 2002, 2003, 2004, 2005, 2006, by Larry Wall and others
79072805 LW	5	*
	6	* You may distribute under the terms of either the GNU General Public
	7	* License or the Artistic License, as specified in the README file.
	8	*
79072805 LW	9	*/
79072805 LW	10
7c60e434	11	/* This structure must the beginning of XPVFM in sv.h */
44a8e56a	12
79072805	13	struct xpvcv {
311a25d9	14	NV xnv_nv; /* numeric value, if any */
79072805 LW	15	STRLEN xpv_cur; /* length of xp_pv as a C string */
79072805 LW	16	STRLEN xpv_len; /* allocated size */
e4305a63	17	union {
311a25d9 NC	18	IV xivu_iv; /* integer value or pv offset */
	19	UV xivu_uv;
	20	void * xivu_p1;
	21	} xiv_u;
79072805 LW	22	MAGIC* xmg_magic; /* magic for scalar array */
	23	HV* xmg_stash; /* class package */
	24
	25	HV * xcv_stash;
bf53b3a5 NC	26	union {
	27	OP * xcv_start;
	28	ANY xcv_xsubany;
	29	} xcv_start_u;
d04ba589 NC	30	union {
	31	OP * xcv_root;
	32	void (xcv_xsub) (pTHX_ CV);
	33	} xcv_root_u;
8990e307	34	GV * xcv_gv;
57843af0	35	char * xcv_file;
b195d487	36	long xcv_depth; /* >= 2 indicates recursive call */
dd2155a4	37	PADLIST * xcv_padlist;
748a9306	38	CV * xcv_outside;
77a005ab	39	cv_flags_t xcv_flags;
a3985cdc DM	40	U32 xcv_outside_seq; /* the COP sequence (at the point of our
	41	* compilation) in the lexically enclosing
	42	* sub */
79072805	43	};
748a9306	44
954c1994	45	/*
ccfc67b7 JH	46	=head1 Handy Values
ccfc67b7 JH	47
954c1994 GS	48	=for apidoc AmU\|\|Nullcv
	49	Null CV pointer.
	50
ccfc67b7 JH	51	=head1 CV Manipulation Functions
ccfc67b7 JH	52
954c1994 GS	53	=for apidoc Am\|HV\|CvSTASH\|CV cv
	54	Returns the stash of the CV.
	55
	56	=cut
	57	*/
	58
79072805	59	#define Nullcv Null(CV*)
a5f75d66	60
79072805	61	#define CvSTASH(sv) ((XPVCV*)SvANY(sv))->xcv_stash
bf53b3a5	62	#define CvSTART(sv) ((XPVCV*)SvANY(sv))->xcv_start_u.xcv_start
d04ba589 NC	63	#define CvROOT(sv) ((XPVCV*)SvANY(sv))->xcv_root_u.xcv_root
d04ba589 NC	64	#define CvXSUB(sv) ((XPVCV*)SvANY(sv))->xcv_root_u.xcv_xsub
bf53b3a5	65	#define CvXSUBANY(sv) ((XPVCV*)SvANY(sv))->xcv_start_u.xcv_xsubany
8990e307	66	#define CvGV(sv) ((XPVCV*)SvANY(sv))->xcv_gv
57843af0	67	#define CvFILE(sv) ((XPVCV*)SvANY(sv))->xcv_file
a636914a RH	68	#ifdef USE_ITHREADS
	69	# define CvFILE_set_from_cop(sv, cop) (CvFILE(sv) = savepv(CopFILE(cop)))
	70	#else
	71	# define CvFILE_set_from_cop(sv, cop) (CvFILE(sv) = CopFILE(cop))
	72	#endif
9ec2a764	73	#define CvFILEGV(sv) (gv_fetchfile(CvFILE(sv)))
79072805 LW	74	#define CvDEPTH(sv) ((XPVCV*)SvANY(sv))->xcv_depth
79072805 LW	75	#define CvPADLIST(sv) ((XPVCV*)SvANY(sv))->xcv_padlist
748a9306	76	#define CvOUTSIDE(sv) ((XPVCV*)SvANY(sv))->xcv_outside
a5f75d66	77	#define CvFLAGS(sv) ((XPVCV*)SvANY(sv))->xcv_flags
a3985cdc	78	#define CvOUTSIDE_SEQ(sv) ((XPVCV*)SvANY(sv))->xcv_outside_seq
a5f75d66	79
5b4563c8 NC	80	#define CVf_METHOD 0x0001 /* CV is explicitly marked as a method */
	81	#define CVf_LOCKED 0x0002 /* CV locks itself or first arg on entry */
	82	#define CVf_LVALUE 0x0004 /* CV return value can be used as lvalue */
	83	#define CVf_ASSERTION 0x0008 /* CV called only when asserting */
	84
	85	#define CVf_WEAKOUTSIDE 0x0010 /* CvOUTSIDE isn't ref counted */
	86	#define CVf_CLONE 0x0020 /* anon CV uses external lexicals */
	87	#define CVf_CLONED 0x0040 /* a clone of one of those */
	88	#define CVf_ANON 0x0080 /* CvGV() can't be trusted */
	89	#define CVf_UNIQUE 0x0100 /* sub is only called once (eg PL_main_cv,
6909cc55 DM	90	* require, eval). Not to be confused
	91	* with the GVf_UNIQUE flag associated
	92	* with the :unique attribute */
5b4563c8	93	#define CVf_NODEBUG 0x0200 /* no DB::sub indirection for this CV
8ebc5c01	94	(esp. useful for special XSUBs) */
5b4563c8 NC	95	#define CVf_CONST 0x0400 /* inlinable sub */
5b4563c8 NC	96	#define CVf_OLDSTYLE 0x0800
d04ba589	97	#define CVf_ISXSUB 0x1000 /* CV is an XSUB, not pure perl. */
7dafbf52	98
d3cea301	99	/* This symbol for optimised communication between toke.c and op.c: */
06492da6	100	#define CVf_BUILTIN_ATTRS (CVf_METHOD\|CVf_LOCKED\|CVf_LVALUE\|CVf_ASSERTION)
a5f75d66 AD	101
	102	#define CvCLONE(cv) (CvFLAGS(cv) & CVf_CLONE)
	103	#define CvCLONE_on(cv) (CvFLAGS(cv) \|= CVf_CLONE)
	104	#define CvCLONE_off(cv) (CvFLAGS(cv) &= ~CVf_CLONE)
	105
	106	#define CvCLONED(cv) (CvFLAGS(cv) & CVf_CLONED)
	107	#define CvCLONED_on(cv) (CvFLAGS(cv) \|= CVf_CLONED)
	108	#define CvCLONED_off(cv) (CvFLAGS(cv) &= ~CVf_CLONED)
	109
	110	#define CvANON(cv) (CvFLAGS(cv) & CVf_ANON)
	111	#define CvANON_on(cv) (CvFLAGS(cv) \|= CVf_ANON)
	112	#define CvANON_off(cv) (CvFLAGS(cv) &= ~CVf_ANON)
79072805	113
67caa1fe	114	#ifdef PERL_XSUB_OLDSTYLE
a5f75d66 AD	115	#define CvOLDSTYLE(cv) (CvFLAGS(cv) & CVf_OLDSTYLE)
	116	#define CvOLDSTYLE_on(cv) (CvFLAGS(cv) \|= CVf_OLDSTYLE)
	117	#define CvOLDSTYLE_off(cv) (CvFLAGS(cv) &= ~CVf_OLDSTYLE)
67caa1fe	118	#endif
07055b4c CS	119
	120	#define CvUNIQUE(cv) (CvFLAGS(cv) & CVf_UNIQUE)
	121	#define CvUNIQUE_on(cv) (CvFLAGS(cv) \|= CVf_UNIQUE)
	122	#define CvUNIQUE_off(cv) (CvFLAGS(cv) &= ~CVf_UNIQUE)
8ebc5c01 PP	123
	124	#define CvNODEBUG(cv) (CvFLAGS(cv) & CVf_NODEBUG)
	125	#define CvNODEBUG_on(cv) (CvFLAGS(cv) \|= CVf_NODEBUG)
	126	#define CvNODEBUG_off(cv) (CvFLAGS(cv) &= ~CVf_NODEBUG)
77a005ab MB	127
	128	#define CvMETHOD(cv) (CvFLAGS(cv) & CVf_METHOD)
	129	#define CvMETHOD_on(cv) (CvFLAGS(cv) \|= CVf_METHOD)
	130	#define CvMETHOD_off(cv) (CvFLAGS(cv) &= ~CVf_METHOD)
	131
	132	#define CvLOCKED(cv) (CvFLAGS(cv) & CVf_LOCKED)
	133	#define CvLOCKED_on(cv) (CvFLAGS(cv) \|= CVf_LOCKED)
	134	#define CvLOCKED_off(cv) (CvFLAGS(cv) &= ~CVf_LOCKED)
1aff0e91	135
cd06dffe GS	136	#define CvLVALUE(cv) (CvFLAGS(cv) & CVf_LVALUE)
	137	#define CvLVALUE_on(cv) (CvFLAGS(cv) \|= CVf_LVALUE)
	138	#define CvLVALUE_off(cv) (CvFLAGS(cv) &= ~CVf_LVALUE)
	139
06492da6 SF	140	#define CvASSERTION(cv) (CvFLAGS(cv) & CVf_ASSERTION)
	141	#define CvASSERTION_on(cv) (CvFLAGS(cv) \|= CVf_ASSERTION)
	142	#define CvASSERTION_off(cv) (CvFLAGS(cv) &= ~CVf_ASSERTION)
	143
1aff0e91 GS	144	#define CvEVAL(cv) (CvUNIQUE(cv) && !SvFAKE(cv))
	145	#define CvEVAL_on(cv) (CvUNIQUE_on(cv),SvFAKE_off(cv))
	146	#define CvEVAL_off(cv) CvUNIQUE_off(cv)
	147
bec31f9a	148	/* BEGIN\|CHECK\|INIT\|END */
1aff0e91 GS	149	#define CvSPECIAL(cv) (CvUNIQUE(cv) && SvFAKE(cv))
	150	#define CvSPECIAL_on(cv) (CvUNIQUE_on(cv),SvFAKE_on(cv))
	151	#define CvSPECIAL_off(cv) (CvUNIQUE_off(cv),SvFAKE_off(cv))
beab0874 JT	152
	153	#define CvCONST(cv) (CvFLAGS(cv) & CVf_CONST)
	154	#define CvCONST_on(cv) (CvFLAGS(cv) \|= CVf_CONST)
	155	#define CvCONST_off(cv) (CvFLAGS(cv) &= ~CVf_CONST)
a4f1a029	156
7dafbf52 DM	157	#define CvWEAKOUTSIDE(cv) (CvFLAGS(cv) & CVf_WEAKOUTSIDE)
	158	#define CvWEAKOUTSIDE_on(cv) (CvFLAGS(cv) \|= CVf_WEAKOUTSIDE)
	159	#define CvWEAKOUTSIDE_off(cv) (CvFLAGS(cv) &= ~CVf_WEAKOUTSIDE)
	160
d04ba589 NC	161	#define CvISXSUB(cv) (CvFLAGS(cv) & CVf_ISXSUB)
	162	#define CvISXSUB_on(cv) (CvFLAGS(cv) \|= CVf_ISXSUB)
	163	#define CvISXSUB_off(cv) (CvFLAGS(cv) &= ~CVf_ISXSUB)
	164
7dafbf52 DM	165	/*
	166	=head1 CV reference counts and CvOUTSIDE
	167
	168	=for apidoc m\|bool\|CvWEAKOUTSIDE\|CV *cv
	169
	170	Each CV has a pointer, C<CvOUTSIDE()>, to its lexically enclosing
	171	CV (if any). Because pointers to anonymous sub prototypes are
	172	stored in C<&> pad slots, it is a possible to get a circular reference,
	173	with the parent pointing to the child and vice-versa. To avoid the
	174	ensuing memory leak, we do not increment the reference count of the CV
	175	pointed to by C<CvOUTSIDE> in the I<one specific instance> that the parent
	176	has a C<&> pad slot pointing back to us. In this case, we set the
	177	C<CvWEAKOUTSIDE> flag in the child. This allows us to determine under what
	178	circumstances we should decrement the refcount of the parent when freeing
	179	the child.
	180
eeb8d49e	181	There is a further complication with non-closure anonymous subs (i.e. those
7dafbf52 DM	182	that do not refer to any lexicals outside that sub). In this case, the
	183	anonymous prototype is shared rather than being cloned. This has the
	184	consequence that the parent may be freed while there are still active
	185	children, eg
	186
	187	BEGIN { $a = sub { eval '$x' } }
	188
	189	In this case, the BEGIN is freed immediately after execution since there
	190	are no active references to it: the anon sub prototype has
	191	C<CvWEAKOUTSIDE> set since it's not a closure, and $a points to the same
	192	CV, so it doesn't contribute to BEGIN's refcount either. When $a is
	193	executed, the C<eval '$x'> causes the chain of C<CvOUTSIDE>s to be followed,
	194	and the freed BEGIN is accessed.
	195
	196	To avoid this, whenever a CV and its associated pad is freed, any
	197	C<&> entries in the pad are explicitly removed from the pad, and if the
	198	refcount of the pointed-to anon sub is still positive, then that
	199	child's C<CvOUTSIDE> is set to point to its grandparent. This will only
	200	occur in the single specific case of a non-closure anon prototype
	201	having one or more active references (such as C<$a> above).
	202
	203	One other thing to consider is that a CV may be merely undefined
	204	rather than freed, eg C<undef &foo>. In this case, its refcount may
	205	not have reached zero, but we still delete its pad and its C<CvROOT> etc.
	206	Since various children may still have their C<CvOUTSIDE> pointing at this
	207	undefined CV, we keep its own C<CvOUTSIDE> for the time being, so that
	208	the chain of lexical scopes is unbroken. For example, the following
	209	should print 123:
	210
	211	my $x = 123;
	212	sub tmp { sub { eval '$x' } }
	213	my $a = tmp();
	214	undef &tmp;
	215	print $a->();
	216
	217	=cut
	218	*/
102d3b8a NC	219
	220	/*
	221	* Local variables:
	222	* c-indentation-style: bsd
	223	* c-basic-offset: 4
	224	* indent-tabs-mode: t
	225	* End:
	226	*
	227	* ex: set ts=8 sts=4 sw=4 noet:
	228	*/