what is "Attempt to free unreferenced scalar"?

[lichtjiang]

I got the following message when one of my perl program exits (it runs multiple threads simultaneously, it has several variable of typess of Thread::Queue and Thread::Semaphore):

Attempt to free unreferenced scalar: SV 0x84f0c00, Perl interpreter: 0x8362c78 during global destruction.

What does this mean and how to track it? Thanks!

 

[MikeLacey]

Hi lichtjiang,

That "sounds" like a Perl bug - Are you running the latest version?

Mike

Hardware is that part of a computer which, when you remove electrical power, doesn't go away.

Want great answers to your Tek-Tips questions? Have a look at faq219-2884

 

[lichtjiang]

Thanks.

mine is "v5.8.8 built for i686-linux-thread-multi" on gentoo linux.

there is known bug similar to this? not very sure

I will have to check my code when I have time later ...

 

[lichtjiang]

forgot to mention that I have 4 threads in total. 3 of them used those queues and semaphores. and there were 3 such message reports for them. no report for the remaining one, which just passed queues and semaphores as arguments.

so, more like some problem w/ my code ...

 

[MikeLacey]

Hi lichtjiang,

How are you getting on with this?

If you're still having problems can I suggest that you write as simple and short a script as possible which shows the errors you're seeing.

This will give you a chance to see clearly where any problems might lie and will also (hopefully) give you a script short enough to be posted here should you need to.

Mike

Hardware is that part of a computer which, when you remove electrical power, doesn't go away.

Want great answers to your Tek-Tips questions? Have a look at faq219-2884

 

[lichtjiang]

Thanks. Mike. That's what I'm thinking to isolate the problem code and find out what is wrong. But just working on other things and didn't find a time for this.

I will do this and post whatever I will find later ...

 

[lichtjiang]

Suppose we have "A.pl" and "B.pm" as follows.

_A.pl_
...
my $dummy;
threads->create("B::c", ($dummy));
...


_B.pm_
...
sub c{...}
...

"Scalars leaked:" occurs for each ref or a hash (replace $dummy with %dummy in above script) that is passed as argument to "B::c".

"Attempt to free unreferenced scalar" always happens in above example when we pass a variable (of any type) in one process to a sub in another module when it is run as a thread.

So, is this a problem of my script or a bug or some friendly message that can be safely ignored? Any comments? Thanks!

 

[lichtjiang]

Forgot to mention,

"Attempt to free unreferenced scalar" happened for each thread called in the way shown above.

 

[MikeLacey]

Hi,

If you say:

my $dummy = 1;
threads->create("B::c", ($dummy));

does that still give you an error?

Mike

Hardware is that part of a computer which, when you remove electrical power, doesn't go away.

Want great answers to your Tek-Tips questions? Have a look at faq219-2884

 

[lichtjiang]

Yes. In all cases that either message was reported, all arguments (scalar, array, hash and their refs) passed to thread "B::c" have been initialized. In "B::c", it also doesn't matter if those arguments appear as lef-side or right-side (the semaphore and queue definitely change their content and I also tried not to use any argument in "B::c" or just print out some scalar or size of some non-scalar.).