Refactor code that gets a mutex and calls into Lua code

src/output-flex.cpp

@@ -48,9 +48,6 @@
 #include <stdexcept>
 #include <string>
 
-// Mutex used to coordinate access to Lua code
-static std::mutex lua_mutex;
-
 // Lua can't call functions on C++ objects directly. This macro defines simple
 // C "trampoline" functions which are called from Lua which get the current
 // context (the output_flex_t object) and call the respective function on the
@@ -896,6 +893,9 @@ int output_flex_t::expire_output_table()
 void output_flex_t::call_lua_function(prepared_lua_function_t func,
                                       osmium::OSMObject const &object)
 {
+    static std::mutex lua_mutex;
+    std::lock_guard<std::mutex> const guard{lua_mutex};
+
     m_calling_context = func.context();
 
     lua_pushvalue(lua_state(), func.index()); // the function to call
@@ -912,13 +912,6 @@ void output_flex_t::call_lua_function(prepared_lua_function_t func,
     m_calling_context = calling_context::main;
 }
 
-void output_flex_t::get_mutex_and_call_lua_function(
-    prepared_lua_function_t func, osmium::OSMObject const &object)
-{
-    std::lock_guard<std::mutex> const guard{lua_mutex};
-    call_lua_function(func, object);
-}
-
 void output_flex_t::pending_way(osmid_t id)
 {
     if (!m_process_way) {
@@ -931,7 +924,7 @@ void output_flex_t::pending_way(osmid_t id)
 
     way_delete(id);
 
-    get_mutex_and_call_lua_function(m_process_way, m_way_cache.get());
+    call_lua_function(m_process_way, m_way_cache.get());
 }
 
 void output_flex_t::select_relation_members()
@@ -940,7 +933,6 @@ void output_flex_t::select_relation_members()
         return;
     }
 
-    std::lock_guard<std::mutex> const guard{lua_mutex};
     call_lua_function(m_select_relation_members, m_relation_cache.get());
 
     // If the function returned nil there is nothing to be marked.
@@ -1020,8 +1012,7 @@ void output_flex_t::pending_relation(osmid_t id)
     delete_from_tables(osmium::item_type::relation, id);
 
     if (m_process_relation) {
-        get_mutex_and_call_lua_function(m_process_relation,
-                                        m_relation_cache.get());
+        call_lua_function(m_process_relation, m_relation_cache.get());
     }
 }
 
@@ -1036,7 +1027,7 @@ void output_flex_t::pending_relation_stage1c(osmid_t id)
     }
 
     m_disable_add_row = true;
-    get_mutex_and_call_lua_function(m_process_relation, m_relation_cache.get());
+    call_lua_function(m_process_relation, m_relation_cache.get());
     m_disable_add_row = false;
 }
 
@@ -1097,7 +1088,7 @@ void output_flex_t::node_add(osmium::Node const &node)
     }
 
     m_context_node = &node;
-    get_mutex_and_call_lua_function(m_process_node, node);
+    call_lua_function(m_process_node, node);
     m_context_node = nullptr;
 }
 
@@ -1110,7 +1101,7 @@ void output_flex_t::way_add(osmium::Way *way)
     }
 
     m_way_cache.init(way);
-    get_mutex_and_call_lua_function(m_process_way, m_way_cache.get());
+    call_lua_function(m_process_way, m_way_cache.get());
 }
 
 void output_flex_t::relation_add(osmium::Relation const &relation)
@@ -1121,7 +1112,7 @@ void output_flex_t::relation_add(osmium::Relation const &relation)
 
     m_relation_cache.init(relation);
     select_relation_members();
-    get_mutex_and_call_lua_function(m_process_relation, relation);
+    call_lua_function(m_process_relation, relation);
 }
 
 void output_flex_t::delete_from_table(table_connection_t *table_connection,
@@ -1511,7 +1502,7 @@ void output_flex_t::reprocess_marked()
         }
         way_delete(id);
         if (m_process_way) {
-            get_mutex_and_call_lua_function(m_process_way, m_way_cache.get());
+            call_lua_function(m_process_way, m_way_cache.get());
         }
     }
 

src/output-flex.hpp

@@ -185,15 +185,12 @@ class output_flex_t : public output_t
 
     /**
      * Call a Lua function that was "prepared" earlier with the OSMObject
-     * as its only parameter.
+     * as its only parameter. Uses a mutex internally to make access to the
+     * Lua environment thread safe.
      */
     void call_lua_function(prepared_lua_function_t func,
                            osmium::OSMObject const &object);
 
-    /// Aquire the lua_mutex and the call `call_lua_function()`.
-    void get_mutex_and_call_lua_function(prepared_lua_function_t func,
-                                         osmium::OSMObject const &object);
-
     void init_lua(std::string const &filename);
 
     // Get the flex table that is as first parameter on the Lua stack.