[p5sagit/p5-mst-13.2.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;
	UV	xivu_uv;
	void *	xivu_p1;
	I32	xivu_i32;	/* depth, >= 2 indicates recursive call */
    }		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;
    PADLIST *	xcv_padlist;
    CV *	xcv_outside;
    U32		xcv_outside_seq; /* the COP sequence (at the point of our
				  * compilation) in the lexically enclosing
				  * sub */
    cv_flags_t	xcv_flags;
};

typedef struct {
    STRLEN	xpv_cur;	/* length of xp_pv as a C string */
    STRLEN	xpv_len;	/* allocated size */
    union {
	IV	xivu_iv;
	UV	xivu_uv;
	void *	xivu_p1;
	I32	xivu_i32;	/* depth, >= 2 indicates recursive call */
    }		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;
    PADLIST *	xcv_padlist;
    CV *	xcv_outside;
    U32		xcv_outside_seq; /* the COP sequence (at the point of our
				  * compilation) in the lexically enclosing
				  * sub */
    cv_flags_t	xcv_flags;
} xpvcv_allocated;

/*
=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)))
#if defined(__GNUC__) && !defined(PERL_GCC_BRACE_GROUPS_FORBIDDEN)
#  define CvDEPTH(sv) (*({const CV *_cv = (CV *)sv; \
			  assert(SvTYPE(_cv) == SVt_PVCV); \
			  &((XPVCV*)SvANY(_cv))->xiv_u.xivu_i32; \
			}))
#else
#  define CvDEPTH(sv)	((XPVCV*)SvANY(sv))->xiv_u.xivu_i32
#endif
#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_ISXSUB	0x0800	/* 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)

#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	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	9	*/
79072805	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	15	STRLEN xpv_cur; /* length of xp_pv as a C string */
79072805	16	STRLEN xpv_len; /* allocated size */
e4305a63	17	union {
bb172083	18	IV xivu_iv;
311a25d9	19	UV xivu_uv;
311a25d9	20	void * xivu_p1;
bb172083	21	I32 xivu_i32; /* depth, >= 2 indicates recursive call */
311a25d9	22	} xiv_u;
79072805	23	MAGIC* xmg_magic; /* magic for scalar array */
	24	HV* xmg_stash; /* class package */
	25
	26	HV * xcv_stash;
bf53b3a5	27	union {
	28	OP * xcv_start;
	29	ANY xcv_xsubany;
	30	} xcv_start_u;
d04ba589	31	union {
	32	OP * xcv_root;
	33	void (xcv_xsub) (pTHX_ CV);
	34	} xcv_root_u;
8990e307	35	GV * xcv_gv;
57843af0	36	char * xcv_file;
dd2155a4	37	PADLIST * xcv_padlist;
748a9306	38	CV * xcv_outside;
a3985cdc	39	U32 xcv_outside_seq; /* the COP sequence (at the point of our
	40	* compilation) in the lexically enclosing
	41	* sub */
bb172083	42	cv_flags_t xcv_flags;
79072805	43	};
748a9306	44
c84c4652	45	typedef struct {
	46	STRLEN xpv_cur; /* length of xp_pv as a C string */
	47	STRLEN xpv_len; /* allocated size */
	48	union {
	49	IV xivu_iv;
	50	UV xivu_uv;
	51	void * xivu_p1;
	52	I32 xivu_i32; /* depth, >= 2 indicates recursive call */
	53	} xiv_u;
	54	MAGIC* xmg_magic; /* magic for scalar array */
	55	HV* xmg_stash; /* class package */
	56
	57	HV * xcv_stash;
	58	union {
	59	OP * xcv_start;
	60	ANY xcv_xsubany;
	61	} xcv_start_u;
	62	union {
	63	OP * xcv_root;
	64	void (xcv_xsub) (pTHX_ CV);
	65	} xcv_root_u;
	66	GV * xcv_gv;
	67	char * xcv_file;
	68	PADLIST * xcv_padlist;
	69	CV * xcv_outside;
	70	U32 xcv_outside_seq; /* the COP sequence (at the point of our
	71	* compilation) in the lexically enclosing
	72	* sub */
	73	cv_flags_t xcv_flags;
	74	} xpvcv_allocated;
	75
954c1994	76	/*
ccfc67b7	77	=head1 Handy Values
ccfc67b7	78
954c1994	79	=for apidoc AmU\|\|Nullcv
	80	Null CV pointer.
	81
ccfc67b7	82	=head1 CV Manipulation Functions
ccfc67b7	83
954c1994	84	=for apidoc Am\|HV\|CvSTASH\|CV cv
	85	Returns the stash of the CV.
	86
	87	=cut
	88	*/
	89
79072805	90	#define Nullcv Null(CV*)
a5f75d66	91
79072805	92	#define CvSTASH(sv) ((XPVCV*)SvANY(sv))->xcv_stash
bf53b3a5	93	#define CvSTART(sv) ((XPVCV*)SvANY(sv))->xcv_start_u.xcv_start
d04ba589	94	#define CvROOT(sv) ((XPVCV*)SvANY(sv))->xcv_root_u.xcv_root
d04ba589	95	#define CvXSUB(sv) ((XPVCV*)SvANY(sv))->xcv_root_u.xcv_xsub
bf53b3a5	96	#define CvXSUBANY(sv) ((XPVCV*)SvANY(sv))->xcv_start_u.xcv_xsubany
8990e307	97	#define CvGV(sv) ((XPVCV*)SvANY(sv))->xcv_gv
57843af0	98	#define CvFILE(sv) ((XPVCV*)SvANY(sv))->xcv_file
a636914a	99	#ifdef USE_ITHREADS
	100	# define CvFILE_set_from_cop(sv, cop) (CvFILE(sv) = savepv(CopFILE(cop)))
	101	#else
	102	# define CvFILE_set_from_cop(sv, cop) (CvFILE(sv) = CopFILE(cop))
	103	#endif
9ec2a764	104	#define CvFILEGV(sv) (gv_fetchfile(CvFILE(sv)))
bb172083	105	#if defined(__GNUC__) && !defined(PERL_GCC_BRACE_GROUPS_FORBIDDEN)
	106	# define CvDEPTH(sv) (({const CV _cv = (CV *)sv; \
	107	assert(SvTYPE(_cv) == SVt_PVCV); \
	108	&((XPVCV*)SvANY(_cv))->xiv_u.xivu_i32; \
	109	}))
	110	#else
	111	# define CvDEPTH(sv) ((XPVCV*)SvANY(sv))->xiv_u.xivu_i32
	112	#endif
79072805	113	#define CvPADLIST(sv) ((XPVCV*)SvANY(sv))->xcv_padlist
748a9306	114	#define CvOUTSIDE(sv) ((XPVCV*)SvANY(sv))->xcv_outside
a5f75d66	115	#define CvFLAGS(sv) ((XPVCV*)SvANY(sv))->xcv_flags
a3985cdc	116	#define CvOUTSIDE_SEQ(sv) ((XPVCV*)SvANY(sv))->xcv_outside_seq
a5f75d66	117
5b4563c8	118	#define CVf_METHOD 0x0001 /* CV is explicitly marked as a method */
	119	#define CVf_LOCKED 0x0002 /* CV locks itself or first arg on entry */
	120	#define CVf_LVALUE 0x0004 /* CV return value can be used as lvalue */
	121	#define CVf_ASSERTION 0x0008 /* CV called only when asserting */
	122
	123	#define CVf_WEAKOUTSIDE 0x0010 /* CvOUTSIDE isn't ref counted */
	124	#define CVf_CLONE 0x0020 /* anon CV uses external lexicals */
	125	#define CVf_CLONED 0x0040 /* a clone of one of those */
	126	#define CVf_ANON 0x0080 /* CvGV() can't be trusted */
	127	#define CVf_UNIQUE 0x0100 /* sub is only called once (eg PL_main_cv,
6909cc55	128	* require, eval). Not to be confused
	129	* with the GVf_UNIQUE flag associated
	130	* with the :unique attribute */
5b4563c8	131	#define CVf_NODEBUG 0x0200 /* no DB::sub indirection for this CV
8ebc5c01	132	(esp. useful for special XSUBs) */
5b4563c8	133	#define CVf_CONST 0x0400 /* inlinable sub */
f73ef291	134	#define CVf_ISXSUB 0x0800 /* CV is an XSUB, not pure perl. */
7dafbf52	135
d3cea301	136	/* This symbol for optimised communication between toke.c and op.c: */
06492da6	137	#define CVf_BUILTIN_ATTRS (CVf_METHOD\|CVf_LOCKED\|CVf_LVALUE\|CVf_ASSERTION)
a5f75d66	138
	139	#define CvCLONE(cv) (CvFLAGS(cv) & CVf_CLONE)
	140	#define CvCLONE_on(cv) (CvFLAGS(cv) \|= CVf_CLONE)
	141	#define CvCLONE_off(cv) (CvFLAGS(cv) &= ~CVf_CLONE)
	142
	143	#define CvCLONED(cv) (CvFLAGS(cv) & CVf_CLONED)
	144	#define CvCLONED_on(cv) (CvFLAGS(cv) \|= CVf_CLONED)
	145	#define CvCLONED_off(cv) (CvFLAGS(cv) &= ~CVf_CLONED)
	146
	147	#define CvANON(cv) (CvFLAGS(cv) & CVf_ANON)
	148	#define CvANON_on(cv) (CvFLAGS(cv) \|= CVf_ANON)
	149	#define CvANON_off(cv) (CvFLAGS(cv) &= ~CVf_ANON)
79072805	150
07055b4c	151	#define CvUNIQUE(cv) (CvFLAGS(cv) & CVf_UNIQUE)
	152	#define CvUNIQUE_on(cv) (CvFLAGS(cv) \|= CVf_UNIQUE)
	153	#define CvUNIQUE_off(cv) (CvFLAGS(cv) &= ~CVf_UNIQUE)
8ebc5c01	154
	155	#define CvNODEBUG(cv) (CvFLAGS(cv) & CVf_NODEBUG)
	156	#define CvNODEBUG_on(cv) (CvFLAGS(cv) \|= CVf_NODEBUG)
	157	#define CvNODEBUG_off(cv) (CvFLAGS(cv) &= ~CVf_NODEBUG)
77a005ab	158
	159	#define CvMETHOD(cv) (CvFLAGS(cv) & CVf_METHOD)
	160	#define CvMETHOD_on(cv) (CvFLAGS(cv) \|= CVf_METHOD)
	161	#define CvMETHOD_off(cv) (CvFLAGS(cv) &= ~CVf_METHOD)
	162
	163	#define CvLOCKED(cv) (CvFLAGS(cv) & CVf_LOCKED)
	164	#define CvLOCKED_on(cv) (CvFLAGS(cv) \|= CVf_LOCKED)
	165	#define CvLOCKED_off(cv) (CvFLAGS(cv) &= ~CVf_LOCKED)
1aff0e91	166
cd06dffe	167	#define CvLVALUE(cv) (CvFLAGS(cv) & CVf_LVALUE)
	168	#define CvLVALUE_on(cv) (CvFLAGS(cv) \|= CVf_LVALUE)
	169	#define CvLVALUE_off(cv) (CvFLAGS(cv) &= ~CVf_LVALUE)
	170
06492da6	171	#define CvASSERTION(cv) (CvFLAGS(cv) & CVf_ASSERTION)
	172	#define CvASSERTION_on(cv) (CvFLAGS(cv) \|= CVf_ASSERTION)
	173	#define CvASSERTION_off(cv) (CvFLAGS(cv) &= ~CVf_ASSERTION)
	174
1aff0e91	175	#define CvEVAL(cv) (CvUNIQUE(cv) && !SvFAKE(cv))
	176	#define CvEVAL_on(cv) (CvUNIQUE_on(cv),SvFAKE_off(cv))
	177	#define CvEVAL_off(cv) CvUNIQUE_off(cv)
	178
bec31f9a	179	/* BEGIN\|CHECK\|INIT\|END */
1aff0e91	180	#define CvSPECIAL(cv) (CvUNIQUE(cv) && SvFAKE(cv))
	181	#define CvSPECIAL_on(cv) (CvUNIQUE_on(cv),SvFAKE_on(cv))
	182	#define CvSPECIAL_off(cv) (CvUNIQUE_off(cv),SvFAKE_off(cv))
beab0874	183
	184	#define CvCONST(cv) (CvFLAGS(cv) & CVf_CONST)
	185	#define CvCONST_on(cv) (CvFLAGS(cv) \|= CVf_CONST)
	186	#define CvCONST_off(cv) (CvFLAGS(cv) &= ~CVf_CONST)
a4f1a029	187
7dafbf52	188	#define CvWEAKOUTSIDE(cv) (CvFLAGS(cv) & CVf_WEAKOUTSIDE)
	189	#define CvWEAKOUTSIDE_on(cv) (CvFLAGS(cv) \|= CVf_WEAKOUTSIDE)
	190	#define CvWEAKOUTSIDE_off(cv) (CvFLAGS(cv) &= ~CVf_WEAKOUTSIDE)
	191
d04ba589	192	#define CvISXSUB(cv) (CvFLAGS(cv) & CVf_ISXSUB)
	193	#define CvISXSUB_on(cv) (CvFLAGS(cv) \|= CVf_ISXSUB)
	194	#define CvISXSUB_off(cv) (CvFLAGS(cv) &= ~CVf_ISXSUB)
	195
7dafbf52	196	/*
	197	=head1 CV reference counts and CvOUTSIDE
	198
	199	=for apidoc m\|bool\|CvWEAKOUTSIDE\|CV *cv
	200
	201	Each CV has a pointer, C<CvOUTSIDE()>, to its lexically enclosing
	202	CV (if any). Because pointers to anonymous sub prototypes are
	203	stored in C<&> pad slots, it is a possible to get a circular reference,
	204	with the parent pointing to the child and vice-versa. To avoid the
	205	ensuing memory leak, we do not increment the reference count of the CV
	206	pointed to by C<CvOUTSIDE> in the I<one specific instance> that the parent
	207	has a C<&> pad slot pointing back to us. In this case, we set the
	208	C<CvWEAKOUTSIDE> flag in the child. This allows us to determine under what
	209	circumstances we should decrement the refcount of the parent when freeing
	210	the child.
	211
eeb8d49e	212	There is a further complication with non-closure anonymous subs (i.e. those
7dafbf52	213	that do not refer to any lexicals outside that sub). In this case, the
	214	anonymous prototype is shared rather than being cloned. This has the
	215	consequence that the parent may be freed while there are still active
	216	children, eg
	217
	218	BEGIN { $a = sub { eval '$x' } }
	219
	220	In this case, the BEGIN is freed immediately after execution since there
	221	are no active references to it: the anon sub prototype has
	222	C<CvWEAKOUTSIDE> set since it's not a closure, and $a points to the same
	223	CV, so it doesn't contribute to BEGIN's refcount either. When $a is
	224	executed, the C<eval '$x'> causes the chain of C<CvOUTSIDE>s to be followed,
	225	and the freed BEGIN is accessed.
	226
	227	To avoid this, whenever a CV and its associated pad is freed, any
	228	C<&> entries in the pad are explicitly removed from the pad, and if the
	229	refcount of the pointed-to anon sub is still positive, then that
	230	child's C<CvOUTSIDE> is set to point to its grandparent. This will only
	231	occur in the single specific case of a non-closure anon prototype
	232	having one or more active references (such as C<$a> above).
	233
	234	One other thing to consider is that a CV may be merely undefined
	235	rather than freed, eg C<undef &foo>. In this case, its refcount may
	236	not have reached zero, but we still delete its pad and its C<CvROOT> etc.
	237	Since various children may still have their C<CvOUTSIDE> pointing at this
	238	undefined CV, we keep its own C<CvOUTSIDE> for the time being, so that
	239	the chain of lexical scopes is unbroken. For example, the following
	240	should print 123:
	241
	242	my $x = 123;
	243	sub tmp { sub { eval '$x' } }
	244	my $a = tmp();
	245	undef &tmp;
	246	print $a->();
	247
	248	=cut
	249	*/
102d3b8a	250
	251	/*
	252	* Local variables:
	253	* c-indentation-style: bsd
	254	* c-basic-offset: 4
	255	* indent-tabs-mode: t
	256	* End:
	257	*
	258	* ex: set ts=8 sts=4 sw=4 noet:
	259	*/