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- Subject: Garbage Collection
- From: "David Burgess" <david@...>
- Date: Mon, 29 Jul 2002 12:05:17 +1000
I have a problem with luaSQL(1.0) (using Lua 4.0.1) that I
cannnot solve and I would appreciate any assistance.
The code I have creates an lua table for ODBC environment,
connection and cursor handles. i.e. hENV, hDBC , hSTMT
I wish to ensure that all handles are closed and all memory
is deallocated when lua_close is called. I also want the
lua garbage collection to close any loose statement(cursor)
handles. However, I dont want statement handles closed when
I am fetching data from them.
The typical lua application that is being written reads like
while (get a user request())
The garbage collection cycle can execute while in
DoSomeThingWithTheResult() which trashes the stmt handle(s).
How do I stop the gc during the DoSomeThingWithTheResult() ?
Finally, the following two C code fragments are used in luaSQL,
which approach is better?
stmt_data *sdata = (stmt_data *) malloc(sizeof(stmt_data));
sdata->stmt_tag = lua_newtag(L);
lua_pushusertag(L, (void *)sdata, sdata->stmt_tag);
lua_pushcclosure(L, stmt_gcmethod, 1);
lua_settagmethod(L, sdata->stmt_tag, "gc");
/* gc method closes handle and does free(sdata) */
lua_settagmethod(L, env->cursor_tag, "gc");
... other code
Cursor_data *cursor = (Cursor_data *)lua_newuserdata(L,
/* Change tag. Otherwise we will create another userdata when we push it.
lua_pushusertag(L, conn, env->conn_tag);
cursor->conn = lua_ref(L, 1);
... other code
/* gc method closes handle, does lua_unref(L, cursor->conn);
and presumably relies on gc to clean up the cursor userdata */