Sandboxed thread stuff

Makefile

@@ -0,0 +1,14 @@
+LUA_CFLAGS != pkg-config lua5.1 --cflags
+LIBTOOL = libtool --tag=CC --silent
+
+preempter.so: preempter.c
+	$(LIBTOOL) --mode=compile cc $(LUA_CFLAGS) -c preempter.c
+	$(LIBTOOL) --mode=link cc -rpath /  $(LUA_CFLAGS) -o libpreempter.la preempter.lo
+	mv .libs/libpreempter.so.0.0.0 preempter.so
+	rm libpreempter.la preempter.lo preempter.o
+
+clean:
+	rm libpreempter.la preempter.lo preempter.o preempter.so
+	rm -rf .libs
+
+main: preempter.so

preempter.c

@@ -0,0 +1,72 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "lua.h"
+#include "lauxlib.h"
+
+lua_Hook old_hook;
+int old_mask;
+int old_count;
+
+void yield_hook(lua_State *L, lua_Debug *ar) {
+  lua_yield(L, 0);
+}
+
+void activate_preempt(lua_State *L, int interval) {
+  old_hook = lua_gethook(L);
+  old_mask = lua_gethookmask(L);
+  old_count = lua_gethookcount(L);
+  lua_sethook(L, yield_hook, LUA_MASKCOUNT, interval);
+}
+
+void disable_preempt(lua_State *L) {
+  lua_sethook(L, old_hook, old_mask, old_count);
+}
+
+// Arguments: instruction count, thread, other arguments
+// Returns: Whatever the thread yields, or error data
+int sandboxed_resume(lua_State *L) {
+  luaL_checktype(L, 1, LUA_TNUMBER);
+  luaL_checktype(L, 2, LUA_TTHREAD);
+  
+  int total_args = lua_gettop(L);
+  int resume_args = total_args - 2;
+  int instr_count = lua_tointeger(L, 1);
+
+  // Push args onto the thread stack
+  lua_State *thread_state = lua_tothread(L, 2);
+  lua_xmove(L, thread_state, resume_args);
+  
+  // Run with preemption
+  activate_preempt(thread_state, instr_count);
+  int res = lua_resume(thread_state, resume_args);
+  disable_preempt(thread_state);
+
+  // Success
+  if (res == LUA_YIELD || res == 0) {
+    lua_pushboolean(L, 1);
+    int resnum = lua_gettop(thread_state);
+    lua_xmove(thread_state, L, resnum);
+    return 1 + resnum;
+  } else { // Error
+    lua_pushboolean(L, 0);
+    lua_xmove(thread_state, L, 1);
+
+    return 2;
+  }
+}
+
+// Arguments: global environment, main function
+int sandboxed_create(lua_State *L) {
+  luaL_checktype(L, 1, LUA_TTABLE);
+  luaL_checktype(L, 1, LUA_TFUNCTION);
+
+  // Put a new thread at the bottom of the stack
+  lua_State *thread_state = lua_newthread(L);
+  lua_insert(L, 1);
+  
+  // Set the function of the thread
+  lua_xmove(L, thread_state, 1);
+  
+  lua_setfenv(L, 1);
+}