3 * Copyright (C) 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1999,
4 * 2000, 2001, 2002, 2003, by Larry Wall and others
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.
11 /* This structure must match XPVCV in B/C.pm and the beginning of XPVFM
15 char * xpv_pv; /* pointer to malloced string (for prototype) */
16 STRLEN xpv_cur; /* length of xp_pv as a C string */
17 STRLEN xpv_len; /* allocated size */
18 IV xof_off; /* integer value */
19 NV xnv_nv; /* numeric value, if any */
20 MAGIC* xmg_magic; /* magic for scalar array */
21 HV* xmg_stash; /* class package */
26 void (*xcv_xsub) (pTHX_ CV*);
30 long xcv_depth; /* >= 2 indicates recursive call */
31 PADLIST * xcv_padlist;
34 U32 xcv_outside_seq; /* the COP sequence (at the point of our
35 * compilation) in the lexically enclosing
42 =for apidoc AmU||Nullcv
45 =head1 CV Manipulation Functions
47 =for apidoc Am|HV*|CvSTASH|CV* cv
48 Returns the stash of the CV.
53 #define Nullcv Null(CV*)
55 #define CvSTASH(sv) ((XPVCV*)SvANY(sv))->xcv_stash
56 #define CvSTART(sv) ((XPVCV*)SvANY(sv))->xcv_start
57 #define CvROOT(sv) ((XPVCV*)SvANY(sv))->xcv_root
58 #define CvXSUB(sv) ((XPVCV*)SvANY(sv))->xcv_xsub
59 #define CvXSUBANY(sv) ((XPVCV*)SvANY(sv))->xcv_xsubany
60 #define CvGV(sv) ((XPVCV*)SvANY(sv))->xcv_gv
61 #define CvFILE(sv) ((XPVCV*)SvANY(sv))->xcv_file
63 # define CvFILE_set_from_cop(sv, cop) (CvFILE(sv) = savepv(CopFILE(cop)))
65 # define CvFILE_set_from_cop(sv, cop) (CvFILE(sv) = CopFILE(cop))
67 #define CvFILEGV(sv) (gv_fetchfile(CvFILE(sv)))
68 #define CvDEPTH(sv) ((XPVCV*)SvANY(sv))->xcv_depth
69 #define CvPADLIST(sv) ((XPVCV*)SvANY(sv))->xcv_padlist
70 #define CvOUTSIDE(sv) ((XPVCV*)SvANY(sv))->xcv_outside
71 #define CvFLAGS(sv) ((XPVCV*)SvANY(sv))->xcv_flags
72 #define CvOUTSIDE_SEQ(sv) ((XPVCV*)SvANY(sv))->xcv_outside_seq
74 #define CVf_CLONE 0x0001 /* anon CV uses external lexicals */
75 #define CVf_CLONED 0x0002 /* a clone of one of those */
76 #define CVf_ANON 0x0004 /* CvGV() can't be trusted */
77 #define CVf_OLDSTYLE 0x0008
78 #define CVf_UNIQUE 0x0010 /* sub is only called once (eg PL_main_cv,
79 * require, eval). Not to be confused
80 * with the GVf_UNIQUE flag associated
81 * with the :unique attribute */
82 #define CVf_NODEBUG 0x0020 /* no DB::sub indirection for this CV
83 (esp. useful for special XSUBs) */
84 #define CVf_METHOD 0x0040 /* CV is explicitly marked as a method */
85 #define CVf_LOCKED 0x0080 /* CV locks itself or first arg on entry */
86 #define CVf_LVALUE 0x0100 /* CV return value can be used as lvalue */
87 #define CVf_CONST 0x0200 /* inlinable sub */
88 #define CVf_WEAKOUTSIDE 0x0400 /* CvOUTSIDE isn't ref counted */
89 #define CVf_ASSERTION 0x0800 /* CV called only when asserting */
91 /* This symbol for optimised communication between toke.c and op.c: */
92 #define CVf_BUILTIN_ATTRS (CVf_METHOD|CVf_LOCKED|CVf_LVALUE|CVf_ASSERTION)
94 #define CvCLONE(cv) (CvFLAGS(cv) & CVf_CLONE)
95 #define CvCLONE_on(cv) (CvFLAGS(cv) |= CVf_CLONE)
96 #define CvCLONE_off(cv) (CvFLAGS(cv) &= ~CVf_CLONE)
98 #define CvCLONED(cv) (CvFLAGS(cv) & CVf_CLONED)
99 #define CvCLONED_on(cv) (CvFLAGS(cv) |= CVf_CLONED)
100 #define CvCLONED_off(cv) (CvFLAGS(cv) &= ~CVf_CLONED)
102 #define CvANON(cv) (CvFLAGS(cv) & CVf_ANON)
103 #define CvANON_on(cv) (CvFLAGS(cv) |= CVf_ANON)
104 #define CvANON_off(cv) (CvFLAGS(cv) &= ~CVf_ANON)
106 #ifdef PERL_XSUB_OLDSTYLE
107 #define CvOLDSTYLE(cv) (CvFLAGS(cv) & CVf_OLDSTYLE)
108 #define CvOLDSTYLE_on(cv) (CvFLAGS(cv) |= CVf_OLDSTYLE)
109 #define CvOLDSTYLE_off(cv) (CvFLAGS(cv) &= ~CVf_OLDSTYLE)
112 #define CvUNIQUE(cv) (CvFLAGS(cv) & CVf_UNIQUE)
113 #define CvUNIQUE_on(cv) (CvFLAGS(cv) |= CVf_UNIQUE)
114 #define CvUNIQUE_off(cv) (CvFLAGS(cv) &= ~CVf_UNIQUE)
116 #define CvNODEBUG(cv) (CvFLAGS(cv) & CVf_NODEBUG)
117 #define CvNODEBUG_on(cv) (CvFLAGS(cv) |= CVf_NODEBUG)
118 #define CvNODEBUG_off(cv) (CvFLAGS(cv) &= ~CVf_NODEBUG)
120 #define CvMETHOD(cv) (CvFLAGS(cv) & CVf_METHOD)
121 #define CvMETHOD_on(cv) (CvFLAGS(cv) |= CVf_METHOD)
122 #define CvMETHOD_off(cv) (CvFLAGS(cv) &= ~CVf_METHOD)
124 #define CvLOCKED(cv) (CvFLAGS(cv) & CVf_LOCKED)
125 #define CvLOCKED_on(cv) (CvFLAGS(cv) |= CVf_LOCKED)
126 #define CvLOCKED_off(cv) (CvFLAGS(cv) &= ~CVf_LOCKED)
128 #define CvLVALUE(cv) (CvFLAGS(cv) & CVf_LVALUE)
129 #define CvLVALUE_on(cv) (CvFLAGS(cv) |= CVf_LVALUE)
130 #define CvLVALUE_off(cv) (CvFLAGS(cv) &= ~CVf_LVALUE)
132 #define CvASSERTION(cv) (CvFLAGS(cv) & CVf_ASSERTION)
133 #define CvASSERTION_on(cv) (CvFLAGS(cv) |= CVf_ASSERTION)
134 #define CvASSERTION_off(cv) (CvFLAGS(cv) &= ~CVf_ASSERTION)
136 #define CvEVAL(cv) (CvUNIQUE(cv) && !SvFAKE(cv))
137 #define CvEVAL_on(cv) (CvUNIQUE_on(cv),SvFAKE_off(cv))
138 #define CvEVAL_off(cv) CvUNIQUE_off(cv)
140 /* BEGIN|CHECK|INIT|END */
141 #define CvSPECIAL(cv) (CvUNIQUE(cv) && SvFAKE(cv))
142 #define CvSPECIAL_on(cv) (CvUNIQUE_on(cv),SvFAKE_on(cv))
143 #define CvSPECIAL_off(cv) (CvUNIQUE_off(cv),SvFAKE_off(cv))
145 #define CvCONST(cv) (CvFLAGS(cv) & CVf_CONST)
146 #define CvCONST_on(cv) (CvFLAGS(cv) |= CVf_CONST)
147 #define CvCONST_off(cv) (CvFLAGS(cv) &= ~CVf_CONST)
149 #define CvWEAKOUTSIDE(cv) (CvFLAGS(cv) & CVf_WEAKOUTSIDE)
150 #define CvWEAKOUTSIDE_on(cv) (CvFLAGS(cv) |= CVf_WEAKOUTSIDE)
151 #define CvWEAKOUTSIDE_off(cv) (CvFLAGS(cv) &= ~CVf_WEAKOUTSIDE)
155 =head1 CV reference counts and CvOUTSIDE
157 =for apidoc m|bool|CvWEAKOUTSIDE|CV *cv
159 Each CV has a pointer, C<CvOUTSIDE()>, to its lexically enclosing
160 CV (if any). Because pointers to anonymous sub prototypes are
161 stored in C<&> pad slots, it is a possible to get a circular reference,
162 with the parent pointing to the child and vice-versa. To avoid the
163 ensuing memory leak, we do not increment the reference count of the CV
164 pointed to by C<CvOUTSIDE> in the I<one specific instance> that the parent
165 has a C<&> pad slot pointing back to us. In this case, we set the
166 C<CvWEAKOUTSIDE> flag in the child. This allows us to determine under what
167 circumstances we should decrement the refcount of the parent when freeing
170 There is a further complication with non-closure anonymous subs (ie those
171 that do not refer to any lexicals outside that sub). In this case, the
172 anonymous prototype is shared rather than being cloned. This has the
173 consequence that the parent may be freed while there are still active
176 BEGIN { $a = sub { eval '$x' } }
178 In this case, the BEGIN is freed immediately after execution since there
179 are no active references to it: the anon sub prototype has
180 C<CvWEAKOUTSIDE> set since it's not a closure, and $a points to the same
181 CV, so it doesn't contribute to BEGIN's refcount either. When $a is
182 executed, the C<eval '$x'> causes the chain of C<CvOUTSIDE>s to be followed,
183 and the freed BEGIN is accessed.
185 To avoid this, whenever a CV and its associated pad is freed, any
186 C<&> entries in the pad are explicitly removed from the pad, and if the
187 refcount of the pointed-to anon sub is still positive, then that
188 child's C<CvOUTSIDE> is set to point to its grandparent. This will only
189 occur in the single specific case of a non-closure anon prototype
190 having one or more active references (such as C<$a> above).
192 One other thing to consider is that a CV may be merely undefined
193 rather than freed, eg C<undef &foo>. In this case, its refcount may
194 not have reached zero, but we still delete its pad and its C<CvROOT> etc.
195 Since various children may still have their C<CvOUTSIDE> pointing at this
196 undefined CV, we keep its own C<CvOUTSIDE> for the time being, so that
197 the chain of lexical scopes is unbroken. For example, the following
201 sub tmp { sub { eval '$x' } }