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Proper fix for CvOUTSIDE weak refcounting
[perl5.git] / cv.h
CommitLineData
a0d0e21e 1/* cv.h
79072805 2 *
eb1102fc 3 * Copyright (c) 1991-2002, Larry Wall
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4 *
5 * You may distribute under the terms of either the GNU General Public
6 * License or the Artistic License, as specified in the README file.
7 *
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8 */
9
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10/* This structure much match XPVCV in B/C.pm and the beginning of XPVFM
11 * in sv.h */
44a8e56a 12
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13struct xpvcv {
14 char * xpv_pv; /* pointer to malloced string */
15 STRLEN xpv_cur; /* length of xp_pv as a C string */
16 STRLEN xpv_len; /* allocated size */
a0d0e21e 17 IV xof_off; /* integer value */
65202027 18 NV xnv_nv; /* numeric value, if any */
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19 MAGIC* xmg_magic; /* magic for scalar array */
20 HV* xmg_stash; /* class package */
21
22 HV * xcv_stash;
23 OP * xcv_start;
24 OP * xcv_root;
acfe0abc 25 void (*xcv_xsub) (pTHX_ CV*);
a0d0e21e 26 ANY xcv_xsubany;
8990e307 27 GV * xcv_gv;
57843af0 28 char * xcv_file;
b195d487 29 long xcv_depth; /* >= 2 indicates recursive call */
dd2155a4 30 PADLIST * xcv_padlist;
748a9306 31 CV * xcv_outside;
77a005ab 32 cv_flags_t xcv_flags;
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33 U32 xcv_outside_seq; /* the COP sequence (at the point of our
34 * compilation) in the lexically enclosing
35 * sub */
79072805 36};
748a9306 37
954c1994 38/*
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39=head1 Handy Values
40
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41=for apidoc AmU||Nullcv
42Null CV pointer.
43
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44=head1 CV Manipulation Functions
45
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46=for apidoc Am|HV*|CvSTASH|CV* cv
47Returns the stash of the CV.
48
49=cut
50*/
51
79072805 52#define Nullcv Null(CV*)
a5f75d66 53
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54#define CvSTASH(sv) ((XPVCV*)SvANY(sv))->xcv_stash
55#define CvSTART(sv) ((XPVCV*)SvANY(sv))->xcv_start
56#define CvROOT(sv) ((XPVCV*)SvANY(sv))->xcv_root
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57#define CvXSUB(sv) ((XPVCV*)SvANY(sv))->xcv_xsub
58#define CvXSUBANY(sv) ((XPVCV*)SvANY(sv))->xcv_xsubany
8990e307 59#define CvGV(sv) ((XPVCV*)SvANY(sv))->xcv_gv
57843af0 60#define CvFILE(sv) ((XPVCV*)SvANY(sv))->xcv_file
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61#ifdef USE_ITHREADS
62# define CvFILE_set_from_cop(sv, cop) (CvFILE(sv) = savepv(CopFILE(cop)))
63#else
64# define CvFILE_set_from_cop(sv, cop) (CvFILE(sv) = CopFILE(cop))
65#endif
9ec2a764 66#define CvFILEGV(sv) (gv_fetchfile(CvFILE(sv)))
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67#define CvDEPTH(sv) ((XPVCV*)SvANY(sv))->xcv_depth
68#define CvPADLIST(sv) ((XPVCV*)SvANY(sv))->xcv_padlist
748a9306 69#define CvOUTSIDE(sv) ((XPVCV*)SvANY(sv))->xcv_outside
a5f75d66 70#define CvFLAGS(sv) ((XPVCV*)SvANY(sv))->xcv_flags
a3985cdc 71#define CvOUTSIDE_SEQ(sv) ((XPVCV*)SvANY(sv))->xcv_outside_seq
a5f75d66 72
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73#define CVf_CLONE 0x0001 /* anon CV uses external lexicals */
74#define CVf_CLONED 0x0002 /* a clone of one of those */
75#define CVf_ANON 0x0004 /* CvGV() can't be trusted */
76#define CVf_OLDSTYLE 0x0008
77#define CVf_UNIQUE 0x0010 /* can't be cloned */
78#define CVf_NODEBUG 0x0020 /* no DB::sub indirection for this CV
8ebc5c01 79 (esp. useful for special XSUBs) */
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80#define CVf_METHOD 0x0040 /* CV is explicitly marked as a method */
81#define CVf_LOCKED 0x0080 /* CV locks itself or first arg on entry */
cd06dffe 82#define CVf_LVALUE 0x0100 /* CV return value can be used as lvalue */
beab0874 83#define CVf_CONST 0x0200 /* inlinable sub */
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84#define CVf_WEAKOUTSIDE 0x0400 /* CvOUTSIDE isn't ref counted */
85
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86/* This symbol for optimised communication between toke.c and op.c: */
87#define CVf_BUILTIN_ATTRS (CVf_METHOD|CVf_LOCKED|CVf_LVALUE)
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88
89#define CvCLONE(cv) (CvFLAGS(cv) & CVf_CLONE)
90#define CvCLONE_on(cv) (CvFLAGS(cv) |= CVf_CLONE)
91#define CvCLONE_off(cv) (CvFLAGS(cv) &= ~CVf_CLONE)
92
93#define CvCLONED(cv) (CvFLAGS(cv) & CVf_CLONED)
94#define CvCLONED_on(cv) (CvFLAGS(cv) |= CVf_CLONED)
95#define CvCLONED_off(cv) (CvFLAGS(cv) &= ~CVf_CLONED)
96
97#define CvANON(cv) (CvFLAGS(cv) & CVf_ANON)
98#define CvANON_on(cv) (CvFLAGS(cv) |= CVf_ANON)
99#define CvANON_off(cv) (CvFLAGS(cv) &= ~CVf_ANON)
79072805 100
67caa1fe 101#ifdef PERL_XSUB_OLDSTYLE
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102#define CvOLDSTYLE(cv) (CvFLAGS(cv) & CVf_OLDSTYLE)
103#define CvOLDSTYLE_on(cv) (CvFLAGS(cv) |= CVf_OLDSTYLE)
104#define CvOLDSTYLE_off(cv) (CvFLAGS(cv) &= ~CVf_OLDSTYLE)
67caa1fe 105#endif
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106
107#define CvUNIQUE(cv) (CvFLAGS(cv) & CVf_UNIQUE)
108#define CvUNIQUE_on(cv) (CvFLAGS(cv) |= CVf_UNIQUE)
109#define CvUNIQUE_off(cv) (CvFLAGS(cv) &= ~CVf_UNIQUE)
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110
111#define CvNODEBUG(cv) (CvFLAGS(cv) & CVf_NODEBUG)
112#define CvNODEBUG_on(cv) (CvFLAGS(cv) |= CVf_NODEBUG)
113#define CvNODEBUG_off(cv) (CvFLAGS(cv) &= ~CVf_NODEBUG)
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114
115#define CvMETHOD(cv) (CvFLAGS(cv) & CVf_METHOD)
116#define CvMETHOD_on(cv) (CvFLAGS(cv) |= CVf_METHOD)
117#define CvMETHOD_off(cv) (CvFLAGS(cv) &= ~CVf_METHOD)
118
119#define CvLOCKED(cv) (CvFLAGS(cv) & CVf_LOCKED)
120#define CvLOCKED_on(cv) (CvFLAGS(cv) |= CVf_LOCKED)
121#define CvLOCKED_off(cv) (CvFLAGS(cv) &= ~CVf_LOCKED)
1aff0e91 122
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123#define CvLVALUE(cv) (CvFLAGS(cv) & CVf_LVALUE)
124#define CvLVALUE_on(cv) (CvFLAGS(cv) |= CVf_LVALUE)
125#define CvLVALUE_off(cv) (CvFLAGS(cv) &= ~CVf_LVALUE)
126
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127#define CvEVAL(cv) (CvUNIQUE(cv) && !SvFAKE(cv))
128#define CvEVAL_on(cv) (CvUNIQUE_on(cv),SvFAKE_off(cv))
129#define CvEVAL_off(cv) CvUNIQUE_off(cv)
130
bec31f9a 131/* BEGIN|CHECK|INIT|END */
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132#define CvSPECIAL(cv) (CvUNIQUE(cv) && SvFAKE(cv))
133#define CvSPECIAL_on(cv) (CvUNIQUE_on(cv),SvFAKE_on(cv))
134#define CvSPECIAL_off(cv) (CvUNIQUE_off(cv),SvFAKE_off(cv))
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135
136#define CvCONST(cv) (CvFLAGS(cv) & CVf_CONST)
137#define CvCONST_on(cv) (CvFLAGS(cv) |= CVf_CONST)
138#define CvCONST_off(cv) (CvFLAGS(cv) &= ~CVf_CONST)
a4f1a029 139
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140#define CvWEAKOUTSIDE(cv) (CvFLAGS(cv) & CVf_WEAKOUTSIDE)
141#define CvWEAKOUTSIDE_on(cv) (CvFLAGS(cv) |= CVf_WEAKOUTSIDE)
142#define CvWEAKOUTSIDE_off(cv) (CvFLAGS(cv) &= ~CVf_WEAKOUTSIDE)
143
144
145/*
146=head1 CV reference counts and CvOUTSIDE
147
148=for apidoc m|bool|CvWEAKOUTSIDE|CV *cv
149
150Each CV has a pointer, C<CvOUTSIDE()>, to its lexically enclosing
151CV (if any). Because pointers to anonymous sub prototypes are
152stored in C<&> pad slots, it is a possible to get a circular reference,
153with the parent pointing to the child and vice-versa. To avoid the
154ensuing memory leak, we do not increment the reference count of the CV
155pointed to by C<CvOUTSIDE> in the I<one specific instance> that the parent
156has a C<&> pad slot pointing back to us. In this case, we set the
157C<CvWEAKOUTSIDE> flag in the child. This allows us to determine under what
158circumstances we should decrement the refcount of the parent when freeing
159the child.
160
161There is a further complication with non-closure anonymous subs (ie those
162that do not refer to any lexicals outside that sub). In this case, the
163anonymous prototype is shared rather than being cloned. This has the
164consequence that the parent may be freed while there are still active
165children, eg
166
167 BEGIN { $a = sub { eval '$x' } }
168
169In this case, the BEGIN is freed immediately after execution since there
170are no active references to it: the anon sub prototype has
171C<CvWEAKOUTSIDE> set since it's not a closure, and $a points to the same
172CV, so it doesn't contribute to BEGIN's refcount either. When $a is
173executed, the C<eval '$x'> causes the chain of C<CvOUTSIDE>s to be followed,
174and the freed BEGIN is accessed.
175
176To avoid this, whenever a CV and its associated pad is freed, any
177C<&> entries in the pad are explicitly removed from the pad, and if the
178refcount of the pointed-to anon sub is still positive, then that
179child's C<CvOUTSIDE> is set to point to its grandparent. This will only
180occur in the single specific case of a non-closure anon prototype
181having one or more active references (such as C<$a> above).
182
183One other thing to consider is that a CV may be merely undefined
184rather than freed, eg C<undef &foo>. In this case, its refcount may
185not have reached zero, but we still delete its pad and its C<CvROOT> etc.
186Since various children may still have their C<CvOUTSIDE> pointing at this
187undefined CV, we keep its own C<CvOUTSIDE> for the time being, so that
188the chain of lexical scopes is unbroken. For example, the following
189should print 123:
190
191 my $x = 123;
192 sub tmp { sub { eval '$x' } }
193 my $a = tmp();
194 undef &tmp;
195 print $a->();
196
197=cut
198*/