[Date Prev][Date Next][Thread Prev][Thread Next]
- Subject: Equality vs. Identity of userdata?
- From: Stephan Herrmann <stephan@...>
- Date: 04 Jun 1998 15:10:59 +0200
What exactly is the behaviour of lua_pushusertag(u,t) ?
I experience it to create a new lua object of type userdata only
once for each value of u. Is this behaviour part of the specification,
or implementation detail? Are two _equal_ userdata objects in Lua
The reason for asking is reference-counting and garbage collection.
I have a C datastructure containing a reference-count and I wanted to
use the same count for references both from C and from Lua. So my
idea was, every time I "export" a C-object to Lua (using lua-pushusertag),
I increment the reference-count. Then I have a "gc" tagmethod, which
calls a free routine that decrements the ref-count and if 0 is reached
frees my resources. So it is transparent, who keeps references
to an object. Whenever the last ref is removed, the object is really freed.
>From my experience I would have to keep two ref-"counts": one for C and
a boolean "count" for Lua, because a userdata seems to be referenced at
most once from Lua. The reverse conclusion seems to be, that two calls
to lua_pushusertag(u,t) with the same u entail at most one call to the
"gc" tagmethod. Is this correct?
A convenient solution would be, if I knew whether lua_pushusertag
created a new object or recycled an existing one. Only in the first
case I would increment my ref-count.