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Hello,
Coincidently, I just finally got *my* garbage
collection working. A few months back, I wrote the list because I had
implemented garbage collection, but none of the gc functions were being
called. Here's some helpful information:
- when
the "gc" tag method is called, on the top of the stack is the userdata
object. This object normally points to the memory location you want to
free. You can get this object using the void *lua_touserdata(lua_State *L,
1) ("1" because the userdata object is at the top of the stack).
Cast the void* pointer to the proper type, then delete the variable (or free()
the memory, if you're using c).
- the
"gc" tag method can only be set for userdata. The reason my garbage
collection didn't work all this time was because I had set the "gc" tag method
for a *table* tag. If you do this, there will be no warning, but no "gc"
tag method will be called.
also,
here's some other helpful troubleshooting information Edgar Toernig and Roberto
sent me when I had my problems:
Some things you should check: First,
are you using the correct tag in all
places? Does the userdata get the
right one? Is the gc-method set for
the same? Then, are you sure you do
not create additional references to
your selection userdata?
Example:
function
foo()
local
x = make_selection(...) -- returns the userdata
y =
x
...
end
Here after executing foo you still
have a reference to your selection
in the global y. And as long as this
reference exists your gc-method
will not be called! An y=nil/0/""/...
is required to remove this ref-
erence. It's not like in some
languages that the destruction of x calls
the destructor (the gc-method).
Destroying the last reference to an
object calls it. And last, did you
create references within the C
program via lua_ref(L, 1)? Make sure
that _each_ lua_ref call has the
appropriate lua_unref (and this can't
be in the gc-method!).
Hope
all this helps,
Falko
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