Implement an internal command to interrupt running Lua scripts

This inserts a debug hook that runs every 256 instructions by
default, which has a minimal impact on performance.

NEWS

@@ -7,6 +7,7 @@ DFHack Future
         Scripts can be enabled with the built-in enable/disable commands
         A new function, reqscript(), is available as a safer alternative to script_environment()
     New internal commands
+        kill-lua: Interrupt running Lua scripts
     New plugins
     New scripts
         burial:  sets all unowned coffins to allow burial ("-pets" to allow pets too)

Readme.rst

@@ -2095,6 +2095,12 @@ Tools:
 * ``sand``: Displays an indicator when sand is present in the currently-selected area, similar to the default clay/stone indicators.
 * ``sticky``: Maintains the selected local area while navigating the world map
 
+kill-lua
+--------
+Interrupts any currently-running Lua scripts. By default, scripts can only be
+interrupted every 256 instructions. Use ``kill-lua force`` to interrupt
+the next instruction.
+
 petcapRemover
 -------------
 This plugin allows you to remove or raise the pet population cap. In vanilla

library/Core.cpp

@@ -753,6 +753,7 @@ command_result Core::runCommand(color_ostream &con, const std::string &first_, v
                 "  cls                   - Clear the console.\n"
                 "  fpause                - Force DF to pause.\n"
                 "  die                   - Force DF to close immediately\n"
+                "  kill-lua              - Stop an active Lua script\n"
                 "  keybinding            - Modify bindings of commands to keys\n"
                 "  script FILENAME       - Run the commands specified in a file.\n"
                 "  sc-script             - Automatically run specified scripts on state change events\n"
@@ -870,6 +871,17 @@ command_result Core::runCommand(color_ostream &con, const std::string &first_, v
         {
             _exit(666);
         }
+        else if(first == "kill-lua")
+        {
+            bool force = false;
+            for (auto it = parts.begin(); it != parts.end(); ++it)
+            {
+                if (*it == "force")
+                    force = true;
+            }
+            if (!Lua::Interrupt(force))
+                con.printerr("Failed to register hook - use 'kill-lua force' to force\n");
+        }
         else if(first == "script")
         {
             if(parts.size() == 1)

library/LuaTools.cpp

@@ -24,6 +24,7 @@ distribution.
 
 #include "Internal.h"
 
+#include <csignal>
 #include <string>
 #include <vector>
 #include <map>
@@ -354,6 +355,35 @@ static int dfhack_lineedit(lua_State *S)
  * Exception handling
  */
 
+volatile std::sig_atomic_t lstop = 0;
+
+static void interrupt_hook (lua_State *L, lua_Debug *ar);
+static void interrupt_init (lua_State *L)
+{
+    lua_sethook(L, interrupt_hook, LUA_MASKCOUNT, 256);
+}
+
+static void interrupt_hook (lua_State *L, lua_Debug *ar)
+{
+    if (lstop)
+    {
+        lstop = 0;
+        interrupt_init(L);  // Restore default settings if necessary
+        luaL_error(L, "interrupted!");
+    }
+}
+
+bool DFHack::Lua::Interrupt (bool force)
+{
+    lua_State *L = Lua::Core::State;
+    if (L->hook != interrupt_hook && !force)
+        return false;
+    if (force)
+        lua_sethook(L, interrupt_hook, LUA_MASKCALL | LUA_MASKRET | LUA_MASKLINE | LUA_MASKCOUNT, 1);
+    lstop = 1;
+    return true;
+}
+
 static int DFHACK_EXCEPTION_META_TOKEN = 0;
 
 static void error_tostring(lua_State *L, bool keep_old = false)
@@ -1561,6 +1591,8 @@ lua_State *DFHack::Lua::Open(color_ostream &out, lua_State *state)
     if (!state)
         state = luaL_newstate();
 
+    interrupt_init(state);
+
     luaL_openlibs(state);
     AttachDFGlobals(state);
 

library/include/LuaTools.h

@@ -263,6 +263,17 @@ namespace DFHack {namespace Lua {
                                         bool (*init)(color_ostream&, lua_State*, void*),
                                         void *arg);
 
+    /**
+     * Attempt to interrupt the currently-executing lua function by raising a lua error
+     * from a lua debug hook, similar to how SIGINT is handled in the lua interpreter (depends/lua/src/lua.c).
+     * The flag set here will only be checked every 256 instructions by default.
+     * Returns false if another debug hook is set and 'force' is false.
+     *
+     * force: Overwrite any existing debug hooks and interrupt the next instruction
+     */
+
+    DFHACK_EXPORT bool Interrupt (bool force=false);
+
     /**
      * Push utility functions
      */