Re[2]: GC and threads

[Dmitriy Iassenev <iassenev@...>]

Hello RLake,

Wednesday, April 28, 2004, 5:05:20 PM, you wrote:

So, is it safe to do the following:

// creating thread
m_thread               = lua_newthread(L);
m_thread_reference     = luaL_ref(L,-1);
lua_pop                (L,1);

// killing finished or yielded thread
lua_pushlightuserdata  (L,m_thread);
luaL_unref             (L,-1,m_thread_reference);
lua_pop                (L,1);
        
Roop> If there is no reference to the thread in Lua, the
Roop> thread may be garbage
Roop> collected at any moment (except when it is running).
Roop> So you must keep a
Roop> reference to it.

Roop> You should probably use luaL_ref and keep the reference
Roop> indexes in your
Roop> C++ objects.

Roop> When you call lua_newthread(L), the new thread object
Roop> will be placed on L's
Roop> stack. If you don't pop it from that stack, then the
Roop> thread is not garbage
Roop> collectable, assuming that L is not garbage collectable
Roop> (i.e., L is the
Roop> main thread). Of course, it may not be a good idea
Roop> to just let things
Roop> accumulate on the main stack.

Roop> A thread is garbage collectable precisely when no
Roop> references to it remain
Roop> (in Lua), regardless of its "state". (Threads
Roop> in Lua are not really threads
Roop> the way you might be thinking of them; they don't
Roop> really "block". The best
Roop> way to think of them, imho, is as separate execution
Roop> stacks.)

Roop> From the stack trace, it looks to me like the thread
Roop> is running and is trying
Roop> to put something in a table, rather than crashing
Roop> on the invocation of pcall.
Roop> It is hard to know what the problem is; it may or
Roop> may not be related to
Roop> garbage collection.

-- 
Best regards,
 Dmitriy                            mailto:iassenev@gsc-game.kiev.ua