Bug #11997 for Clone: Clone dies horribly when Scalar::Util::weaken is around

Fri Mar 25 03:01:37 2005 adamk [...] cpan.org - Ticket created

Subject:

Clone dies horribly when Scalar::Util::weaken is around

Clone and Scalar::Util::weaken are absolutely fatal to each other. The most canonical example I can produce so far is: perl -MClone=clone -MScalar::Util=weaken -wle '$x = { a => "worked\n" }; $y = $x; weaken($y); print clone($x)->{a};' When this runs, it fails to clone, generating only an empty hashref, then when the scope ends, it panics perl.

Fri Mar 25 03:22:40 2005 adamk [...] cpan.org - Correspondence added

From the look of it, once $y is weakened, the hash gets a magic back-reference attached to it. Before the weakening of $y DB<5> Dump($x) SV = RV(0x817be1c) at 0x816329c REFCNT = 1 FLAGS = (ROK) RV = 0x8163350 SV = PVHV(0x84cdbf8) at 0x8163350 REFCNT = 2 FLAGS = (SHAREKEYS) IV = 1 NV = 0 ARRAY = 0x82f65d0 (0:7, 1:1) hash quality = 100.0% KEYS = 1 FILL = 1 MAX = 7 RITER = -1 EITER = 0x0 Elt "a" HASH = 0xca2e9442 SV = PV(0x814cea4) at 0x81633a4 REFCNT = 1 FLAGS = (POK,pPOK) PV = 0x8164990 "worked\n"\0 CUR = 7 LEN = 8 After the weakening of $y DB<6> Dump($x) SV = RV(0x817be1c) at 0x816329c REFCNT = 1 FLAGS = (ROK) RV = 0x8163350 SV = PVHV(0x84cdbf8) at 0x8163350 REFCNT = 1 FLAGS = (RMG,SHAREKEYS) IV = 1 NV = 0 MAGIC = 0x8574020 MG_VIRTUAL = &PL_vtbl_backref MG_TYPE = PERL_MAGIC_backref(<) MG_FLAGS = 0x02 REFCOUNTED MG_OBJ = 0x8525484 SV = PVAV(0x84c4a54) at 0x8525484 REFCNT = 2 FLAGS = () IV = 0 NV = 0 ARRAY = 0x84aafb8 FILL = 0 MAX = 3 ARYLEN = 0x0 FLAGS = (REAL) Elt No. 0 SV = RV(0x817be58) at 0x81632cc REFCNT = 1 FLAGS = (ROK,WEAKREF,IsUV) RV = 0x8163350 SV = PVHV(0x84cdbf8) at 0x8163350 REFCNT = 1 FLAGS = (RMG,SHAREKEYS) IV = 1 NV = 0 MAGIC = 0x8574020 MG_VIRTUAL = &PL_vtbl_backref MG_TYPE = PERL_MAGIC_backref(<) MG_FLAGS = 0x02 REFCOUNTED MG_OBJ = 0x8525484 SV = PVAV(0x84c4a54) at 0x8525484 REFCNT = 2 FLAGS = () IV = 0 NV = 0 ARRAY = 0x84aafb8 FILL = 0 MAX = 3 ARYLEN = 0x0 FLAGS = (REAL) ARRAY = 0x82f65d0 (0:7, 1:1) hash quality = 100.0% KEYS = 1 FILL = 1 MAX = 7 RITER = -1 EITER = 0x0 ARRAY = 0x82f65d0 (0:7, 1:1) hash quality = 100.0% KEYS = 1 FILL = 1 MAX = 7 RITER = -1 EITER = 0x0 Elt "a" HASH = 0xca2e9442 SV = PV(0x814cea4) at 0x81633a4 REFCNT = 1 FLAGS = (POK,pPOK) PV = 0x8164990 "worked\n"\0 CUR = 7 LEN = 8 The #perl channel recommends taking the cloning code from sv.c to handle the various types of SV cloning that you don't current handle. Specifically (in my case) that for PERL_MAGIC_backref(<)

Wed Apr 20 12:03:54 2005 rdf [...] cpan.org - Correspondence added

Hi, I just uploaded a new version that has a fix for the MAGIC_backref problem. Looking at the perl code there are other cases that will probably fail as well. In my copious free time, I'll have to come up with some test cases and a better way to handle the magic.

Wed Apr 20 12:03:54 2005 rdf [...] cpan.org - Status changed from 'new' to 'open'

Thu May 05 18:36:53 2005 rdf [...] cpan.org - Status changed from 'open' to 'resolved'