Revises EventHandler members & updates hash function

- converts `freq` and `eventHandler` (i.e. the callback) to `const`
- removes the non-const `when` from the hash computation

Author: cppcooper

library/include/modules/EventManager.h

@@ -44,8 +44,8 @@ namespace DFHack {
 
         struct EventHandler {
             typedef void (*callback_t)(color_ostream&, void*); //called when the event happens
-            callback_t eventHandler;
-            int32_t freq; //how often event is allowed to fire (in ticks) use 0 to always fire when possible
+            const callback_t eventHandler;
+            const int32_t freq; //how often event is allowed to fire (in ticks) use 0 to always fire when possible
             int32_t when = -1; //when to fire event (global tick count)
 
             EventHandler(callback_t eventHandlerIn, int32_t freqIn) :
@@ -146,7 +146,6 @@ namespace std {
             size_t r = 17;
             const size_t m = 65537;
             r = m*(r+(intptr_t)h.eventHandler);
-            r = m*(r+h.when);
             r = m*(r+h.freq);
             return r;
         }

library/modules/EventManager.cpp

@@ -94,7 +94,7 @@ int32_t DFHack::EventManager::registerTick(EventHandler handler, int32_t when, P
         }
     }
     handler.when = when;
-    tickQueue.insert(pair<int32_t, EventHandler>(handler.when, handler));
+    tickQueue.emplace(handler.when, handler);
     // we don't track this handler, this allows registerTick to retain the old behaviour of needing to re-register the tick event
     //handlers[EventType::TICK].insert(pair<Plugin*,EventHandler>(plugin,handler));
     // since the event isn't added to the handlers, we don't need to unregister these events

plugins/devel/eventExample.cpp

@@ -97,12 +97,12 @@ command_result eventExample(color_ostream& out, vector<string>& parameters) {
     EventManager::registerTick(timeHandler, 4, plugin_self);
     EventManager::registerTick(timeHandler, 8, plugin_self);
     int32_t t = EventManager::registerTick(timeHandler, 16, plugin_self);
-    timeHandler.freq = t;
+    timeHandler.when = t;
     EventManager::unregister(EventManager::EventType::TICK, timeHandler, plugin_self);
     t = EventManager::registerTick(timeHandler, 32, plugin_self);
     t = EventManager::registerTick(timeHandler, 32, plugin_self);
     t = EventManager::registerTick(timeHandler, 32, plugin_self);
-    timeHandler.freq = t;
+    timeHandler.when = t;
     EventManager::unregister(EventManager::EventType::TICK, timeHandler, plugin_self);
     EventManager::unregister(EventManager::EventType::TICK, timeHandler, plugin_self);