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- Subject: Re: lua_close() locks but never unlocks... ?
- From: Rici Lake <lua@...>
- Date: Thu, 2 Feb 2006 20:40:15 -0500
On 2-Feb-06, at 8:24 PM, Chris wrote:
On 2/2/06, Rici Lake <email@example.com> wrote:
Yes, I think that answers my question. You simply can not access a
Lua state from another thread, even with the internal locking enabled.
You cannot randomly access a Lua state's stack while that Lua state is
actively running a script.
Is a shame. :(
Well, without knowing what exactly you're trying to do, it's hard to
offer much in the way of advice, but there is certainly nothing
stopping you from setting up a single Lua state ("universe") and using
multiple Lua threads, each in their own native thread (or not). In that
case, you would only have a single state and a single mutex, and the
various threads could (cautiously) share data.
I personally wouldn't use that strategy, for a number of reasons:
1) The lua_lock() mechanism only protects the integrity of Lua data
structures. It does not protect the integrity of data held in Lua
tables, for example, in the sense that it does not provide any sort of
atomic update. That is, unless you provide your own locking mechanism,
you cannot guarantee that the following is atomic:
x = lua_tonumber(L, -1);
lua_pushnumber(L, x + 1);
The global "foo" could be modified by another thread at any point in
2) Unnecessary lock contention is fairly likely if you're running a
number of threads in an SMP environment. Most of the time, the various
threads are probably not using shared resources.
3) The frequent calls to lua_lock() and lua_unlock() slow things down a
On the other hand, there is nothing stopping you from creating a
binding to an arbitrary shared structure, which the various threads
could access through a userdata. That structure would need its own
lock, of course. You could make that look really a lot like the
userdata were a native table. So that way you could run multiple Lua
universes without the lua_lock() mechanism, as long as you ensured that
each Lua universe was only active in one thread (at a time).