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- Subject: GCed dynamic libraries
- From: Edgar Toernig <froese@...>
- Date: Thu, 24 Jun 2004 03:46:00 +0200
Hi,
Some days ago I mentioned a scheme to make dynamic libraries
garbage collected. Here's a sample implementation. As a
bonus, dynamic libraries get a private registry.
The concept:
The only references to a dynamic library that Lua cares
about are C-functions exported via lua_pushcclosure.
All other possible references (through userdata or light
userdata) are never accessed by the Lua core itself.
After loading a library, there's only one C-function, the
start- or init-function of the library. This function in
turn may export other functions, and so on.
If the C-closure of the start-function gets a reference
to the library and one makes sure that this reference is
propagated through to future C-closures created by the
library, the garbage collector would be able to detect
when a library is no longer referenced.
While working on an implementation I noticed, that a lot
of libraries make use of the registry, either by storing
metatables there or luaL_ref-erences or something else.
This of course would prohibit any garbage collection -
there would always be a reference from the registry to
the dynamic library.
As a consequence, I made the registry the commonly shared
object of all exported C-closures of a particular library.
All C-closures which are not created by a dynamic library
get the same "coreregistry". Later on I noticed that some
code needs access to this coreregistry to store systemwide
data (luaL_getn/setn and the debug-hook code) so I added
an additional special index (LUA_COREREGISTRYINDEX).
The dynamic loader:
Changes are straight forward. Create a new registry and
a userdata with a handle for the library. The userdata is
set up to unload the library when it is collected. Then the
userdata is stored into the registry and the C-closure for
the start-function with the new registry is created.
[The last step is a little bit weird due to the fact that
there's no direct way to change the registry of an arbitrary
closure, only lua_replace(L, LUA_REGISTRYINDEX) which changes
the registry of the currently active closure.]
On-exit handlers:
There's no special code for an on-exit-function. It can
easily be implemented through the regular API. Just create
a userdata object, assign the on-exit function as the __gc
function and stored it in the registry. (luaL_onexit?)
Finally, the code:
diff -ru lua-5.0-orig/src/lobject.h lua-5.0-gcso/src/lobject.h
--- lua-5.0-orig/src/lobject.h Tue Mar 18 13:50:04 2003
+++ lua-5.0-gcso/src/lobject.h Tue Jun 22 00:18:53 2004
@@ -260,6 +260,7 @@
typedef struct CClosure {
ClosureHeader;
lua_CFunction f;
+ TObject _registry;
TObject upvalue[1];
} CClosure;
diff -ru lua-5.0-orig/src/lstate.h lua-5.0-gcso/src/lstate.h
--- lua-5.0-orig/src/lstate.h Thu Feb 27 12:52:30 2003
+++ lua-5.0-gcso/src/lstate.h Wed Jun 23 15:58:39 2004
@@ -49,7 +49,8 @@
#define gt(L) (&L->_gt)
/* registry */
-#define registry(L) (&G(L)->_registry)
+#define registry(L) (&clvalue((L)->base-1)->c._registry)
+#define coreregistry(L) (&clvalue((L)->stack)->c._registry)
/* extra stack space to handle TM calls and some other extras */
@@ -117,7 +118,6 @@
lu_mem GCthreshold;
lu_mem nblocks; /* number of `bytes' currently allocated */
lua_CFunction panic; /* to be called in unprotected errors */
- TObject _registry;
TObject _defaultmeta;
struct lua_State *mainthread;
Node dummynode[1]; /* common node array for all empty tables */
diff -ru lua-5.0-orig/src/lstate.c lua-5.0-gcso/src/lstate.c
--- lua-5.0-orig/src/lstate.c Thu Apr 3 15:35:34 2003
+++ lua-5.0-gcso/src/lstate.c Thu Jun 24 00:41:16 2004
@@ -98,7 +98,6 @@
g->strt.nuse = 0;
g->strt.hash = NULL;
setnilvalue(defaultmeta(L));
- setnilvalue(registry(L));
luaZ_initbuffer(L, &g->buff);
g->panic = default_panic;
g->rootgc = NULL;
@@ -114,7 +113,10 @@
sethvalue(defaultmeta(L), luaH_new(L, 0, 0));
hvalue(defaultmeta(L))->metatable = hvalue(defaultmeta(L));
sethvalue(gt(L), luaH_new(L, 0, 4)); /* table of globals */
- sethvalue(registry(L), luaH_new(L, 4, 4)); /* registry */
+ /* create dummy function with core registry */
+ setclvalue(L->stack, luaF_newCclosure(L, 0));
+ clvalue(L->stack)->c.f = NULL;
+ sethvalue(coreregistry(L), luaH_new(L, 4, 4)); /* registry */
luaS_resize(L, MINSTRTABSIZE); /* initial size of string table */
luaT_init(L);
luaX_init(L);
@@ -165,6 +167,7 @@
preinit_state(L1);
L1->l_G = L->l_G;
stack_init(L1, L); /* init stack */
+ setobj2n(L1->stack, L->stack); /* share dummy func with core registry */
setobj2n(gt(L1), gt(L)); /* share table of globals */
return L1;
}
diff -ru lua-5.0-orig/include/lua.h lua-5.0-gcso/include/lua.h
--- lua-5.0-orig/include/lua.h Tue Mar 18 13:31:39 2003
+++ lua-5.0-gcso/include/lua.h Wed Jun 23 15:56:30 2004
@@ -28,7 +28,8 @@
** pseudo-indices
*/
#define LUA_REGISTRYINDEX (-10000)
-#define LUA_GLOBALSINDEX (-10001)
+#define LUA_COREREGISTRYINDEX (-10001)
+#define LUA_GLOBALSINDEX (-10002)
#define lua_upvalueindex(i) (LUA_GLOBALSINDEX-(i))
diff -ru lua-5.0-orig/src/lapi.c lua-5.0-gcso/src/lapi.c
--- lua-5.0-orig/src/lapi.c Mon Apr 7 16:36:08 2003
+++ lua-5.0-gcso/src/lapi.c Thu Jun 24 00:22:34 2004
@@ -52,6 +52,7 @@
}
else switch (idx) { /* pseudo-indices */
case LUA_REGISTRYINDEX: return registry(L);
+ case LUA_COREREGISTRYINDEX: return coreregistry(L);
case LUA_GLOBALSINDEX: return gt(L);
default: {
TObject *func = (L->base - 1);
@@ -450,6 +451,7 @@
api_checknelems(L, n);
cl = luaF_newCclosure(L, n);
cl->c.f = fn;
+ setobj2n(&cl->c._registry, registry(L)); /* share callers registry */
L->top -= n;
while (n--)
setobj2n(&cl->c.upvalue[n], L->top+n);
@@ -702,6 +704,7 @@
Closure *cl;
cl = luaF_newCclosure(L, 0);
cl->c.f = c->func;
+ setobj2n(&cl->c._registry, registry(L)); /* share callers registry */
setclvalue(L->top, cl); /* push function */
incr_top(L);
setpvalue(L->top, c->ud); /* push only argument */
diff -ru lua-5.0-orig/src/lgc.c lua-5.0-gcso/src/lgc.c
--- lua-5.0-orig/src/lgc.c Thu Apr 3 15:35:34 2003
+++ lua-5.0-gcso/src/lgc.c Tue Jun 22 01:18:45 2004
@@ -205,6 +205,7 @@
static void traverseclosure (GCState *st, Closure *cl) {
if (cl->c.isC) {
int i;
+ markobject(st, &cl->c._registry);
for (i=0; i<cl->c.nupvalues; i++) /* mark its upvalues */
markobject(st, &cl->c.upvalue[i]);
}
@@ -444,7 +445,6 @@
static void markroot (GCState *st, lua_State *L) {
global_State *g = st->g;
markobject(st, defaultmeta(L));
- markobject(st, registry(L));
traversestack(st, g->mainthread);
if (L != g->mainthread) /* another thread is running? */
markvalue(st, L); /* cannot collect it */
diff -ru lua-5.0-orig/src/lib/lauxlib.c lua-5.0-gcso/src/lib/lauxlib.c
--- lua-5.0-orig/src/lib/lauxlib.c Mon Apr 7 16:35:00 2003
+++ lua-5.0-gcso/src/lib/lauxlib.c Thu Jun 24 00:16:16 2004
@@ -264,7 +264,7 @@
static void getsizes (lua_State *L) {
- lua_rawgeti(L, LUA_REGISTRYINDEX, ARRAYSIZE_REF);
+ lua_rawgeti(L, LUA_COREREGISTRYINDEX, ARRAYSIZE_REF);
if (lua_isnil(L, -1)) { /* no `size' table? */
lua_pop(L, 1); /* remove nil */
lua_newtable(L); /* create it */
@@ -274,7 +274,7 @@
lua_pushliteral(L, "k");
lua_rawset(L, -3); /* metatable(N).__mode = "k" */
lua_pushvalue(L, -1);
- lua_rawseti(L, LUA_REGISTRYINDEX, ARRAYSIZE_REF); /* store in register */
+ lua_rawseti(L, LUA_COREREGISTRYINDEX, ARRAYSIZE_REF); /* store in register */
}
}
diff -ru lua-5.0-orig/src/lib/ldblib.c lua-5.0-gcso/src/lib/ldblib.c
--- lua-5.0-orig/src/lib/ldblib.c Thu Apr 3 15:35:34 2003
+++ lua-5.0-gcso/src/lib/ldblib.c Thu Jun 24 00:16:33 2004
@@ -140,7 +140,7 @@
static const char *const hooknames[] =
{"call", "return", "line", "count", "tail return"};
lua_pushlightuserdata(L, (void *)&KEY_HOOK);
- lua_rawget(L, LUA_REGISTRYINDEX);
+ lua_rawget(L, LUA_COREREGISTRYINDEX);
if (lua_isfunction(L, -1)) {
lua_pushstring(L, hooknames[(int)ar->event]);
if (ar->currentline >= 0)
@@ -187,7 +187,7 @@
}
lua_pushlightuserdata(L, (void *)&KEY_HOOK);
lua_pushvalue(L, 1);
- lua_rawset(L, LUA_REGISTRYINDEX); /* set new hook */
+ lua_rawset(L, LUA_COREREGISTRYINDEX); /* set new hook */
return 0;
}
@@ -200,7 +200,7 @@
lua_pushliteral(L, "external hook");
else {
lua_pushlightuserdata(L, (void *)&KEY_HOOK);
- lua_rawget(L, LUA_REGISTRYINDEX); /* get hook */
+ lua_rawget(L, LUA_COREREGISTRYINDEX); /* get hook */
}
lua_pushstring(L, unmakemask(mask, buff));
lua_pushnumber(L, (lua_Number)lua_gethookcount(L));
diff -ru lua-5.0-orig/src/lib/loadlib.c lua-5.0-gcso/src/lib/loadlib.c
--- lua-5.0-orig/src/lib/loadlib.c Mon Apr 7 22:11:53 2003
+++ lua-5.0-gcso/src/lib/loadlib.c Wed Jun 23 05:26:31 2004
@@ -45,6 +45,10 @@
#include <dlfcn.h>
+static void pushinitfunc(lua_State *L, void *libhandle, lua_CFunction initf);
+static void *getunloadhandle(lua_State *L);
+
+
static int loadlib(lua_State *L)
{
const char *path=luaL_checkstring(L,1);
@@ -55,8 +59,7 @@
lua_CFunction f=(lua_CFunction) dlsym(lib,init);
if (f!=NULL)
{
- lua_pushlightuserdata(L,lib);
- lua_pushcclosure(L,f,1);
+ pushinitfunc(L, lib, f);
return 1;
}
}
@@ -68,6 +71,14 @@
return 3;
}
+static int unloadlib(lua_State *L)
+{
+ void **lib = getunloadhandle(L);
+
+ if (lib)
+ dlclose(*lib);
+ return 0;
+}
#endif
@@ -92,6 +103,10 @@
#include <windows.h>
+static void pushinitfunc(lua_State *L, void *libhandle, lua_CFunction initf);
+static void getunloadhandle(lua_State *L);
+
+
static void pusherror(lua_State *L)
{
int error=GetLastError();
@@ -113,8 +128,7 @@
lua_CFunction f=(lua_CFunction) GetProcAddress(lib,init);
if (f!=NULL)
{
- lua_pushlightuserdata(L,lib);
- lua_pushcclosure(L,f,1);
+ pushinitfunc(L, lib, f);
return 1;
}
}
@@ -125,11 +139,73 @@
return 3;
}
+static int unloadlib(lua_State *L)
+{
+ HINSTANCE *lib = getunloadhandle(L);
+
+ if (lib)
+ FreeLibrary(*lib);
+ return 0;
+}
+
#endif
-#ifndef LOADLIB
+#ifdef LOADLIB
+
+/* common code */
+
+static int pushinitfunc2(lua_State *L) /* initf,regtable */
+{
+ lua_replace(L, LUA_REGISTRYINDEX);
+ lua_pushcfunction(L, lua_touserdata(L, 1));
+ return 1;
+}
+
+static void pushinitfunc(lua_State *L, void *handle, lua_CFunction initf)
+{
+ /* ud = setmetatable(newuserdata(handle), <upval1>) */
+ /* pushinitfunc2(initf, { [ud]=true }) */
+ lua_pushcfunction(L, pushinitfunc2);
+ lua_pushlightuserdata(L, initf);
+ lua_newtable(L);
+ lua_boxpointer(L, handle);
+ lua_pushvalue(L, lua_upvalueindex(1));
+ lua_setmetatable(L, -2);
+ lua_pushboolean(L, 1);
+ lua_rawset(L, -3);
+ lua_call(L, 2, 1);
+}
+
+static void *getunloadhandle(lua_State *L)
+{
+ void *lib = NULL;
+ printf("*unload\n");
+
+ if (lua_getmetatable(L, 1) && lua_rawequal(L, -1, lua_upvalueindex(1)))
+ {
+ lib = lua_touserdata(L, 1);
+ lua_pushnil(L);
+ lua_setmetatable(L, 1);
+ }
+ return lib;
+}
+
+LUALIB_API int luaopen_loadlib (lua_State *L)
+{
+ lua_newtable(L);
+ lua_pushliteral(L, "__gc");
+ lua_pushvalue(L, -2);
+ lua_pushcclosure(L, unloadlib, 1);
+ lua_rawset(L, -3);
+ lua_pushcclosure(L, loadlib, 1);
+ lua_setglobal(L, "loadlib");
+ return 0;
+}
+
+
+#else
/* Fallback for other systems */
/*
@@ -170,13 +246,13 @@
lua_pushliteral(L,"absent");
return 3;
}
-#endif
LUALIB_API int luaopen_loadlib (lua_State *L)
{
lua_register(L,"loadlib",loadlib);
return 0;
}
+#endif
/*
* Here are some links to available implementations of dlfcn and
--------------
Todo: Debug hooks have no registry; only the coreregistry
is available. Workaround: store the registry in the
coreregistry as long as the hook is registered and
within the hook fetch it from there.
Ciao, ET.
