Perl Error Attempt To Free Unreferenced Scalar Sv
here for a quick overview of the site Help Center Detailed answers to any questions you might have Meta Discuss the workings and policies of this site About Us Learn more about Stack Overflow the company Business Learn more about hiring developers or posting ads with us Stack Overflow Questions Jobs Documentation Tags Users Badges Ask Question x Dismiss Join the Stack Overflow Community Stack Overflow is a community of 6.2 million programmers, just like you, helping each other. Join them; it only takes a minute: Sign up How to investigate “ Attempt to free unreferenced scalar” up vote 7 down vote favorite A Perl script (which uses a load of locally-written modules, and is under active development) has just started producing sporadic " Attempt to free unreferenced scalar: SV 0xa6e685c, Perl interpreter: 0x96d9008 during global destruction." messages. This are always repeatable, in the sense that a particular sequence of commands always produces the message if it ever does, but I've not managed to isolate a simple or stand-alone case which elicits it. In particular, I haven't yet seen it when running the script from the Perl debugger (I can get it when debugging a script which uses IPC::Open3 to run my target script.) I realise that this is just possibly a bug in Perl, but much more likely to be something I'm doing, very likely round my calls to SVN::Client; but I'm stumped for a way to investigate it, and I wondered if anybody had any pointers. Perl 5.10.0; Various versions of Fedora Linux. I'm going to try it on Perl 5.12, but unless it manifests there too, it won't really help me. Edit: a particular case which reliably gives the message in 5.10 doesn't in 5.12. Unfortunately that doesn't really tell me anything. perl debugging share|improve this question edited Jul 28 '11 at 9:59 asked Jul 27 '11 at 17:10 Colin Fine 2,7191321 2 5.14 is the current release of Perl. 5.12 and 5.10 are rather old. But anyway, compile perl with debugging so that you can see what created the SV at 0xa6e685c. This should point you in the right direction. (My guess is that SVN::Client or another XS module is broken.) –jrockway Jul 27 '11 at 18:42 add a comment| 5 Answers 5 active oldest votes up vote 2 down vote Late answer, but I wrote a long article about this particular topic that should help with debugging: The Dreaded "Attempt to free unreferenced scalar". share|improve this answer answered Jun 27 '13 at 11:55 tsee 4,63111125 Whilst this may theoretically answer the question, it would be preferable to include the essential parts of the answer here, and provide the link for reference. –Hasturkun Jun 2
here for a quick overview of the site Help Center Detailed answers to any questions you might have Meta Discuss the workings and policies of this site About Us Learn more about Stack Overflow the company Business Learn more about hiring developers or posting ads with us Stack Overflow Questions Jobs Documentation Tags Users Badges Ask Question x Dismiss Join the Stack Overflow Community Stack Overflow is a community of 6.2 million programmers, just like you, helping each other. Join them; it only takes a minute: Sign up Can “Attempt to free unreferenced scalar” errors be safely ignored? up vote 5 down vote favorite I haven't figured out http://stackoverflow.com/questions/6848420/how-to-investigate-attempt-to-free-unreferenced-scalar what's causing it, but I'm wondering if there are any consequences to the error (warning?) message "Attempt to free unreferenced scalar: SV 0x825b790 during global destruction". To the untrained eye, it would appear that since the compiler bothered to detect the problem, then it didn't go ahead and re-delete the unreferenced memory. Is this just telling me that my programming is sloppy? or are there real problems happening that I should be concerned http://stackoverflow.com/questions/24618243/can-attempt-to-free-unreferenced-scalar-errors-be-safely-ignored about? Background: it's not my code, I don't really have time to hunt down the problem, and I should note it's happening right at the end of the program. perl share|improve this question asked Jul 7 '14 at 19:22 jk. 3,62821518 Not, not at all. It's a very serious problem. It means memory that shouldn't be read or changed is being read or changed. –ikegami May 26 '15 at 15:59 add a comment| 1 Answer 1 active oldest votes up vote 8 down vote accepted It's a bug in an XS module or in Perl itself. It means there's been a request to deallocate a scalar that has already been deallocated. This indicates that some code is holding a pointer it thinks is valid, but isn't. This can result in code writing to memory that the code shouldn't be modifying, which can result in data integrity problems, segfaults, etc. It was detected when the program exits, but the problem happened could have happened at any time. You are subject to problems from the time it was freed until the error was emitted. For example, use Inline C => <<'__EOI__'; void buggy(SV* sv) { SvREFCNT_dec(sv); } __EOI__ my $x; buggy($x); # $x is no longer allocated here, but I could still try to use it. Output: Atte
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