reduce the interrupt check rate

docs/dev/Lua API.rst

@@ -681,6 +681,10 @@ Miscellaneous
   both from the curry call and the closure call itself. I.e.,
   ``curry(func,a,b)(c,d)`` equals ``func(a,b,c,d)``.
 
+* ``dfhack.dump_interrupt_timing_data()``
+
+  Dumps the internal log of times between interrupt callbacks, as a table of integers.
+  Each entry is the difference between two consecutive interrupts, in microseconds.
 
 Locking and finalization
 ------------------------

library/LuaTools.cpp

@@ -505,11 +505,19 @@ 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);
+    lua_sethook(L, interrupt_hook, LUA_MASKCOUNT, 16384);
 }
 
+constexpr auto interrupt_log_buffer_size = 64;
+using timer = std::chrono::high_resolution_clock;
+static std::array<timer::time_point, interrupt_log_buffer_size> interrupt_log_buffer;
+static size_t interrupt_log_buffer_index = 0;
+
 static void interrupt_hook (lua_State *L, lua_Debug *ar)
 {
+    interrupt_log_buffer[interrupt_log_buffer_index] = timer::now();
+    interrupt_log_buffer_index = (interrupt_log_buffer_index + 1) % interrupt_log_buffer_size;
+
     if (lstop)
     {
         lstop = 0;
@@ -518,6 +526,24 @@ static void interrupt_hook (lua_State *L, lua_Debug *ar)
     }
 }
 
+static int dfhack_dump_interrupt_timing_data(lua_State* L)
+{
+    int base = lua_gettop(L);
+    lua_createtable(L, interrupt_log_buffer_size-1, 0);
+    auto last = timer::now();
+    for (auto idx = 0; idx < interrupt_log_buffer_size; idx++)
+    {
+        auto i = (idx + interrupt_log_buffer_index) % interrupt_log_buffer_size;
+        auto dur = interrupt_log_buffer[i] - last;
+        last = interrupt_log_buffer[i];
+        if (idx>0) {
+            lua_pushinteger(L, std::chrono::duration_cast<std::chrono::microseconds>(dur).count());
+            lua_rawseti(L, base + 1, idx);
+        }
+    }
+    return 1;
+}
+
 bool DFHack::Lua::Interrupt (bool force)
 {
     lua_State *L = DFHack::Core::getInstance().getLuaState(true);
@@ -1498,6 +1524,7 @@ static const luaL_Reg dfhack_funcs[] = {
     { "with_suspend", lua_dfhack_with_suspend },
     { "open_plugin", dfhack_open_plugin },
     { "curry", dfhack_curry },
+    { "dump_interrupt_timing_data", dfhack_dump_interrupt_timing_data },
     { NULL, NULL }
 };