From f2a5f525261e2dc73c04bc81ec4f4bc513d78e78 Mon Sep 17 00:00:00 2001
From: Vas Crabb <vas@vastheman.com>
Date: Wed, 8 Mar 2023 04:09:22 +1100
Subject: [PATCH] Lua: Be more strict with concurrency and multiple contexts.

---
 plugins/console/init.lua        | 10 +++++-----
 src/frontend/mame/luaengine.cpp | 35 ++++++++++++++++++++++-----------
 2 files changed, 29 insertions(+), 16 deletions(-)

diff --git a/plugins/console/init.lua b/plugins/console/init.lua
index 33f698fc0cb..f9e712a66a9 100644
--- a/plugins/console/init.lua
+++ b/plugins/console/init.lua
@@ -45,8 +45,8 @@ function console.startplugin()
 			function(c, str)
 				status = str
 				yield()
-				for k, v in pairs(status) do
-					ln.addcompletion(c, v)
+				for candidate in status:gmatch('([^\001]+)') do
+					ln.addcompletion(c, candidate)
 				end
 			end)
 		local ret = ln.linenoise('$PROMPT')
@@ -207,9 +207,9 @@ function console.startplugin()
 		local str, strs, expr, sep = simplify_expression(line, word)
 		contextual_list(expr, sep, str, word, strs)
 		if #matches == 0 then
-			return { line }
+			return line
 		elseif #matches == 1 then
-			return { start .. matches[1] }
+			return start .. matches[1]
 		end
 		print("")
 		result = { }
@@ -217,7 +217,7 @@ function console.startplugin()
 			print(v)
 			table.insert(result, start .. v)
 		end
-		return result
+		return table.concat(result, '\001')
 	end
 
 	emu.register_start(function()
diff --git a/src/frontend/mame/luaengine.cpp b/src/frontend/mame/luaengine.cpp
index 04b68b75e9a..063f01dc5c9 100644
--- a/src/frontend/mame/luaengine.cpp
+++ b/src/frontend/mame/luaengine.cpp
@@ -63,7 +63,7 @@ namespace {
 struct thread_context
 {
 private:
-	sol::object m_result;
+	std::string m_result;
 	std::mutex m_guard;
 	std::condition_variable m_sync;
 
@@ -73,7 +73,7 @@ public:
 
 	bool start(char const *scr)
 	{
-		std::unique_lock<std::mutex> lock(m_guard);
+		std::unique_lock<std::mutex> caller_lock(m_guard);
 		if (m_busy)
 			return false;
 
@@ -87,6 +87,7 @@ public:
 					thstate["package"]["preload"]["lfs"] = &luaopen_lfs;
 					thstate["package"]["preload"]["linenoise"] = &luaopen_linenoise;
 					sol::load_result res = thstate.load(script);
+					std::unique_lock<std::mutex> result_lock(m_guard, std::defer_lock);
 					if (res.valid())
 					{
 						sol::protected_function func = res.get<sol::protected_function>();
@@ -94,17 +95,24 @@ public:
 								"yield",
 								[this, &thstate]()
 								{
-									std::unique_lock<std::mutex> lock(m_guard);
+									std::unique_lock<std::mutex> yield_lock(m_guard);
 									m_result = thstate["status"];
 									m_yield = true;
-									m_sync.wait(lock);
+									m_sync.wait(yield_lock);
 									m_yield = false;
 									thstate["status"] = m_result;
 								});
 						auto ret = func();
+						result_lock.lock();
 						if (ret.valid())
 						{
-							m_result = ret.get<sol::object>();
+							auto result = ret.get<std::optional<char const *> >();
+							if (!result)
+								osd_printf_error("[LUA ERROR] in thread: return value must be string\n");
+							else if (!*result)
+								m_result.clear();
+							else
+								m_result = *result;
 						}
 						else
 						{
@@ -114,10 +122,12 @@ public:
 					}
 					else
 					{
+						result_lock.lock();
 						sol::error err = res;
 						osd_printf_error("[LUA ERROR] when loading script for thread: %s\n", err.what());
 					}
-					m_busy = false; // FIXME: shouldn't do this when not holding the lock
+					assert(result_lock);
+					m_busy = false;
 			});
 		m_busy = true;
 		m_yield = false;
@@ -125,23 +135,26 @@ public:
 		return true;
 	}
 
-	void resume(sol::object val)
+	void resume(char const *val)
 	{
 		std::unique_lock<std::mutex> lock(m_guard);
 		if (m_yield)
 		{
-			m_result = val;
+			if (val)
+				m_result = val;
+			else
+				m_result.clear();
 			m_sync.notify_all();
 		}
 	}
 
-	sol::object result()
+	char const *result()
 	{
 		std::unique_lock<std::mutex> lock(m_guard);
 		if (m_busy && !m_yield)
-			return sol::lua_nil;
+			return "";
 		else
-			return m_result;
+			return m_result.c_str();
 	}
 };