Added lua_datum to wrap the common task of retaining references to Lua objects in the Lua registry.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@7477 c06c8d41-db1a-0410-9941-cceddc491573

4 files changed, 130 insertions, 20 deletions

diff --git a/crawl-ref/source/clua.cc b/crawl-ref/source/clua.cc
index 477d772a40..9fa1a79a9a 100644
--- a/crawl-ref/source/clua.cc
+++ b/crawl-ref/source/clua.cc
@@ -84,12 +84,17 @@ CLua::CLua(bool managed)
 
 CLua::~CLua()
 {
+    // Copy the listener vector, because listeners may remove
+    // themselves from the listener list when we notify them of a
+    // shutdown.
+    const std::vector<lua_shutdown_listener*> slisteners = shutdown_listeners;
+    for (int i = 0, size = slisteners.size(); i < size; ++i)
+        slisteners[i]->shutdown(*this);
     shutting_down = true;
     if (_state)
         lua_close(_state);
 }
 
-// This has the disadvantage of repeatedly trying init_lua if it fails.
 lua_State *CLua::state()
 {
     if (!_state)
@@ -597,7 +602,7 @@ void CLua::init_lua()
 
     _state = managed_vm? lua_newstate(_clua_allocator, this) : luaL_newstate();
     if (!_state)
-        return;
+        end(1, false, "Unable to create Lua state.");
 
     lua_stack_cleaner clean(_state);
 
@@ -658,6 +663,22 @@ void CLua::load_cmacro()
     execfile("clua/macro.lua", true, true);
 }
 
+void CLua::add_shutdown_listener(lua_shutdown_listener *listener)
+{
+    if (std::find(shutdown_listeners.begin(), shutdown_listeners.end(),
+                  listener) == shutdown_listeners.end())
+        shutdown_listeners.push_back(listener);
+}
+
+void CLua::remove_shutdown_listener(lua_shutdown_listener *listener)
+{
+    std::vector<lua_shutdown_listener*>::iterator i =
+        std::find(shutdown_listeners.begin(), shutdown_listeners.end(),
+                  listener);
+    if (i != shutdown_listeners.end())
+        shutdown_listeners.erase(i);
+}
+
 /////////////////////////////////////////////////////////////////////
 
 static void _clua_register_metatable(lua_State *ls, const char *tn,
@@ -2849,3 +2870,62 @@ std::string quote_lua_string(const std::string &s)
 {
     return replace_all_of(replace_all_of(s, "\\", "\\\\"), "\"", "\\\"");
 }
+
+/////////////////////////////////////////////////////////////////////
+
+lua_datum::lua_datum(CLua &_lua, int stackpos, bool pop)
+    : need_cleanup(true), lua(_lua)
+{
+    // Store the datum in the registry indexed by "this".
+    lua_pushvalue(lua, stackpos);
+    lua_pushlightuserdata(lua, this);
+    // Move the key (this) before the value.
+    lua_insert(lua, -2);
+    lua_settable(lua, LUA_REGISTRYINDEX);
+
+    if (pop && stackpos < 0)
+        lua_pop(lua, -stackpos);
+
+    lua.add_shutdown_listener(this);
+}
+
+lua_datum::lua_datum(const lua_datum &o)
+    : need_cleanup(true), lua(o.lua)
+{
+    lua_pushlightuserdata(lua, this);
+    o.push();
+    lua_settable(lua, LUA_REGISTRYINDEX);
+
+    lua.add_shutdown_listener(this);
+}
+
+void lua_datum::push() const
+{
+    lua_pushlightuserdata(lua, const_cast<lua_datum*>(this));
+    lua_gettable(lua, LUA_REGISTRYINDEX);
+
+    // The value we saved is now on top of the Lua stack.
+}
+
+lua_datum::~lua_datum()
+{
+    cleanup();
+}
+
+void lua_datum::shutdown(CLua &)
+{
+    cleanup();
+}
+
+void lua_datum::cleanup()
+{
+    if (need_cleanup)
+    {
+        need_cleanup = false;
+        lua.remove_shutdown_listener(this);
+
+        lua_pushlightuserdata(lua, this);
+        lua_pushnil(lua);
+        lua_settable(lua, LUA_REGISTRYINDEX);
+    }
+}
diff --git a/crawl-ref/source/clua.h b/crawl-ref/source/clua.h
index f5a0050cca..ae465aa3a0 100644
--- a/crawl-ref/source/clua.h
+++ b/crawl-ref/source/clua.h
@@ -57,6 +57,36 @@ private:
     static lua_clua_map lua_map;
 };
 
+class lua_shutdown_listener
+{
+public:
+    virtual void shutdown(CLua &lua) = 0;
+};
+
+// A convenience class to keep a reference to a lua object on the stack.
+// This is useful to hang on to things that cannot be directly retrieved by
+// C++ code, such as Lua function references.
+class lua_datum : public lua_shutdown_listener
+{
+public:
+    lua_datum(CLua &lua, int stackpos = -1, bool pop = true);
+    lua_datum(const lua_datum &other);
+
+    void shutdown(CLua &lua);
+
+    ~lua_datum();
+
+    // Push the datum onto the Lua stack.
+    void push() const;
+
+private:
+    bool need_cleanup;
+    CLua &lua;
+
+private:
+    void cleanup();
+};
+
 class CLua
 {
 public:
@@ -95,6 +125,9 @@ public:
     void fnreturns(const char *params, ...);
     bool runhook(const char *hook, const char *params, ...);
 
+    void add_shutdown_listener(lua_shutdown_listener *);
+    void remove_shutdown_listener(lua_shutdown_listener *);
+
     static int file_write(lua_State *ls);
     static int loadfile(lua_State *ls, const char *file,
                         bool trusted = false, bool die_on_fail = false);
@@ -128,6 +161,8 @@ private:
     sfset sourced_files;
     unsigned long uniqindex;
 
+    std::vector<lua_shutdown_listener*> shutdown_listeners;
+
 private:
     void init_lua();
     void set_error(int err, lua_State *ls = NULL);
diff --git a/crawl-ref/source/mapmark.cc b/crawl-ref/source/mapmark.cc
index 5f0942ef2e..7fadb6330e 100644
--- a/crawl-ref/source/mapmark.cc
+++ b/crawl-ref/source/mapmark.cc
@@ -188,13 +188,6 @@ map_lua_marker::map_lua_marker(const std::string &s, const std::string &,
 
 map_lua_marker::~map_lua_marker()
 {
-    // Remove the Lua marker table from the registry.
-    if (initialised)
-    {
-        lua_pushlightuserdata(dlua, this);
-        lua_pushnil(dlua);
-        lua_settable(dlua, LUA_REGISTRYINDEX);
-    }
 }
 
 map_marker *map_lua_marker::clone() const
@@ -216,22 +209,21 @@ void map_lua_marker::check_register_table()
     }
 
     // Got a table. Save it in the registry.
-
-    // Key is this.
-    lua_pushlightuserdata(dlua, this);
-    // Move key before value.
-    lua_insert(dlua, -2);
-    lua_settable(dlua, LUA_REGISTRYINDEX);
-
+    marker_table.reset(new lua_datum(dlua));
     initialised = true;
 }
 
 bool map_lua_marker::get_table() const
 {
-    // First save the unmarshall Lua function.
-    lua_pushlightuserdata(dlua, const_cast<map_lua_marker*>(this));
-    lua_gettable(dlua, LUA_REGISTRYINDEX);
-    return (lua_istable(dlua, -1));
+    if (marker_table.get())
+    {
+        marker_table->push();
+        return (lua_istable(dlua, -1));
+    }
+    else
+    {
+        return (false);
+    }
 }
 
 void map_lua_marker::write(writer &outf) const
diff --git a/crawl-ref/source/mapmark.h b/crawl-ref/source/mapmark.h
index 3efc40e591..07d89331be 100644
--- a/crawl-ref/source/mapmark.h
+++ b/crawl-ref/source/mapmark.h
@@ -16,6 +16,7 @@
 #include "luadgn.h"
 #include <map>
 #include <string>
+#include <memory>
 
 //////////////////////////////////////////////////////////////////////////
 // Map markers
@@ -117,6 +118,8 @@ public:
         throw (std::string);
 private:
     bool initialised;
+    std::auto_ptr<lua_datum> marker_table;
+
 private:
     void check_register_table();
     bool get_table() const;