From cb84aa19c45aac2d527404dc4a0a683f6102ab9f Mon Sep 17 00:00:00 2001
From: Pavel Labath <pavelo@centrum.sk>
Date: Tue, 14 Jun 2011 17:02:07 +0200
Subject: Lua exceptions can now outlive thier lua context

---
 src/FbTk/Luamm.cc |  9 +++++----
 src/FbTk/Luamm.hh | 14 +++++++++++++-
 2 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/src/FbTk/Luamm.cc b/src/FbTk/Luamm.cc
index c4ea2e0..563be9c 100644
--- a/src/FbTk/Luamm.cc
+++ b/src/FbTk/Luamm.cc
@@ -173,7 +173,7 @@ namespace lua {
     }
 
     exception::exception(state *l)
-        : std::runtime_error(get_error_msg(l)), L(l)
+        : std::runtime_error(get_error_msg(l)), L(l), L_valid(l->get_valid())
     {
         L->checkstack(1);
 
@@ -184,7 +184,7 @@ namespace lua {
     }
 
     exception::exception(const exception &other)
-        : std::runtime_error(other), L(other.L)
+        : std::runtime_error(other), L(other.L), L_valid(other.L_valid)
     {
         L->checkstack(2);
 
@@ -196,7 +196,7 @@ namespace lua {
 
     exception::~exception() throw()
     {
-        if(not L)
+        if(not L or not *L_valid)
             return;
         L->checkstack(1);
 
@@ -217,7 +217,7 @@ namespace lua {
     }
 
     state::state()
-        : cobj(luaL_newstate())
+        : cobj(luaL_newstate()), valid(new bool(true))
     {
         if(cobj == NULL) {
             // docs say this can happen only in case of a memory allocation error
@@ -249,6 +249,7 @@ namespace lua {
             luaL_openlibs(cobj);
         }
         catch(...) {
+            *valid = false;
             lua_close(cobj);
             throw;
         }
diff --git a/src/FbTk/Luamm.hh b/src/FbTk/Luamm.hh
index f2084e7..1ba9cbe 100644
--- a/src/FbTk/Luamm.hh
+++ b/src/FbTk/Luamm.hh
@@ -31,6 +31,7 @@
 #include <lua.h>
 #include <lualib.h>
 
+#include "RefCount.hh"
 #include "Slot.hh"
 
 namespace lua {
@@ -84,6 +85,7 @@ namespace lua {
      */
     class exception: public std::runtime_error {
         state *L;
+        FbTk::RefCount<const bool> L_valid;
         int key;
 
         static std::string get_error_msg(state *L);
@@ -152,9 +154,19 @@ namespace lua {
         bool safe_compare(lua_CFunction trampoline, int index1, int index2);
         void do_pushclosure(int n);
 
+        /**
+         * The pointed-to value is true if this object still exists. We need this because the
+         * exceptions have to know if they may reference it to remove the saved lua exception. If
+         * this object is destroyed then the exception was already collected by the garbage
+         * colletor and referencing this would generate a segfault.
+         */
+        FbTk::RefCount<bool> valid;
+
     public:
         state();
-        ~state() { lua_close(cobj); }
+        ~state() { *valid = false; lua_close(cobj); }
+
+        FbTk::RefCount<const bool> get_valid() const { return valid; }
 
         /*
          * Lua functions come in three flavours
-- 
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