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Re: perlembed: mortalize an AV, get "Attempt to free unreferenced scalar" - don't mortalize, leaks memory

by hv (Parson)
on Jul 11, 2006 at 12:20 UTC ( #560423=note: print w/ replies, xml ) Need Help??


in reply to perlembed: mortalize an AV, get "Attempt to free unreferenced scalar" - don't mortalize, leaks memory

Let me try to explain how this works:

Normally, the way you control the lifetime of a variable is to increment its refcount at the start of its life (or at the point you start to care about it), and decrement the refcount when you're done with it:

increment do stuff decrement

Mostly it works exactly like this: our interest in the variable is restricted to a balanced scope within our code, and we increment on one side and decrement on the other side. We don't know or care who else has an interest in it, as long as we can be sure the variable won't go away within the scope of our interest in it.

The one time this doesn't work is when you are returning a value - at the point of return you stop caring about it, so you'd normally want to decrement its refcount. But it needs to live long enough for the caller to see it.

There is an implicit vocabulary here - fail to decrement it and it is "immortal"; decrement it too early and it "dies" too soon. The solution is to "mortalize" it - tell perl to decrement its refcount, but not just yet. This is what mortalizing a variable does

So if you are not returning the arrayref, you don't want to mortalize it - just increment the refcount at the start of its life, and decrement it when you're done.

Hope this helps,

Hugo


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