Initialise Lua's pseudo-RNG from C from a good source

GLib has an internal pseudo-RNG that it initialises from /dev/urandom.
This commit adds code that uses this RNG to initialise various random
number generators that can be used by Lua.

This also removes some Lua code that initialises the random number
generator badly.

Signed-off-by: Uli Schlachter <psychon@znc.in>

awesome.c

@@ -71,6 +71,33 @@ static float main_loop_iteration_limit = 0.1;
 /** A pipe that is used to asynchronously handle SIGCHLD */
 static int sigchld_pipe[2];
 
+/* Initialise various random number generators */
+static void
+init_rng(void)
+{
+    /* LuaJIT uses its own, internal RNG, so initialise that */
+    lua_State *L = globalconf_get_lua_State();
+
+    /* Get math.randomseed */
+    lua_getglobal(L, "math");
+    lua_getfield(L, -1, "randomseed");
+
+    /* Push a seed */
+    lua_pushnumber(L, g_random_int() + g_random_double());
+
+    /* Call math.randomseed */
+    lua_call(L, 1, 0);
+
+    /* Remove "math" global */
+    lua_pop(L, 1);
+
+    /* Lua 5.1, Lua 5.2, and (sometimes) Lua 5.3 use rand()/srand() */
+    srand(g_random_int());
+
+    /* When Lua 5.3 is built with LUA_USE_POSIX, it uses random()/srandom() */
+    srandom(g_random_int());
+}
+
 /** Call before exiting.
  */
 void
@@ -864,6 +891,7 @@ main(int argc, char **argv)
     /* init lua */
     luaA_init(&xdg, &searchpath);
     string_array_wipe(&searchpath);
+    init_rng();
 
     ewmh_init_lua();
 

lib/gears/filesystem.lua

@@ -153,8 +153,6 @@ function filesystem.get_dir(d)
     end
 end
 
-math.randomseed( os.clock() % 1 * 1e6 )
-
 --- Get the name of a random file from a given directory.
 -- @tparam string path The directory to search.
 -- @tparam[opt] table exts Specific extensions to limit the search to. eg:`{ "jpg", "png" }`